Figures of Merit Guiding Research on Organic ... - ACS Publications

Subscriber access provided by UNIV OF SCIENCES PHILADELPHIA

Feature Article

Figures of Merit Guiding Research on Organic Solar Cells Thomas Kirchartz, Pascal Kaienburg, and Derya Baran J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.8b01598 • Publication Date (Web): 02 Mar 2018 Downloaded from http://pubs.acs.org on March 4, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

The Journal of Physical Chemistry C is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 46 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Journal of Physical Chemistry

Figures of Merit Guiding Research on Organic Solar Cells Thomas Kirchartz1,2, Pascal Kaienburg1, and Derya Baran1,3 1

IEK5-Photovoltaics, Forschungszentrum Jülich, 52425 Jülich, Germany Faculty of Engineering and CENIDE, University of Duisburg-Essen, Carl-Benz-Str. 199, 47057 Duisburg, Germany 3 Physical Sciences and Engineering Division, KAUST Solar Center (KSC), King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia 2

Abstract While substantial progress in the efficiency of polymer-based solar cells was possible by optimizing the energy levels of the polymer and more recently also the acceptor molecule, further progress beyond 10 % efficiency requires a number of criteria to be fulfilled simultaneously, namely low energy level offsets at the donor-acceptor heterojunction, low open-circuit voltage losses due to non-radiative recombination and efficient charge transport and collection. In this feature article we discuss these criteria considering thermodynamic limits, their correlation to photocurrent and photovoltage and effects on the fill factor. Each criterion is quantified by a figure of merit (FOM) that directly relates to device performance. To ensure a wide applicability, we focus on FOMs that are easily accessible from common experiments. We demonstrate the relevance of these FOMs by looking at the historic and recent achievements of organic solar cells. We hope that the presented FOMs are or will become a valuable tool to evaluate, monitor and guide further development of new organic absorber materials for solar cells.

1

ACS Paragon Plus Environment

The Journal of Physical Chemistry 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

I. Introduction Power conversion efficiencies (PCE) of polymer-based solar cells (PSC) have risen steadily in the last 15 years and nowadays there are several material combinations with efficiencies exceeding 10%.1-10 and several with more than 12 %.11,12 However, the increase of peak efficiencies of polymer:fullerene solar cells has decelerated with substantial progress being made with novel non-fullerene acceptors that now start surpassing efficiencies of polymer:fullerene solar cells.11 Despite the promising development of non-fullerene acceptors, progress substantially beyond the 10% level will be more difficult than the path towards 10%. During different times in the development of solar cell technologies in general and organic photovoltaics in particular there have been certain guidelines and optimization criteria that technology development was based on. One obvious example in the case of organic photovoltaics are the redshift of the absorption onset from polymers with absorption onsets around 2.0 eV like PPV or P3HT to novel lower band gap polymers with absorption onsets in the 1.4 – 1.6 eV range13,14 that lead to a better match with the solar spectrum. Another example is the optimization of energy levels at the donor-acceptor heterointerface13,15-18 leading to increased open-circuit voltages that drove much of the development in efficiencies. Whenever there are such guidelines or optimization criteria, a research community will create - ideally quantitative - figures of merit that can be used as a measuring stick to evaluate progress, to find outstanding materials or devices and to identify either the potential for further improvement or the necessity to change or expand the optimization criteria used. In solar cell research, efficiency (PCE or η), open-circuit voltage (Voc), short-circuit current (Jsc) and fill factor (FF) are the four dominant figures of merit that are used to judge device quality; however, taken in isolation they lack informative value. An open-circuit voltage of 1 V for instance is relatively meaningless without information about the shape of the absorption edge, the band gap (Eg) and the type of material used. Thus, a valuable figure 2 ACS Paragon Plus Environment

Page 2 of 46

Page 3 of 46 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


of merit might be based on the four main device parameters mentioned above but in addition it will create the context necessary to allow comparison between different devices and materials. Here we aim to give an overview over various figures-of-merit that have been used - implicitly or explicitly- as a guideline for improving organic solar cell efficiencies and show how the technology and therefore also these FOMs are likely to develop in the future. Understanding the reasons for high or low solar cell efficiencies is a task that may be approached considering different layers of abstraction and complexity. Of course, the final goal of understanding would ideally be one that connects what we now about the properties of molecules and their microstructure after film formation with properties such as recombination coefficients, mobilities, absorption coefficients, and energy level alignment. Finally, one could then relate the parameters describing recombination, transport and absorption with the key performance parameters of the photovoltaic device. The scope of this article is to focus on the second step rather than the first one and thus on the issues that are close to the properties of the solar cell itself. After our discussion on the thermodynamics of photovoltage losses, the energy level alignment in donor-acceptor solar cells and the question of electronic quality and high fill factors, we will conclude with a brief conclusion and outlook of recent developments and how further research can overcome the existing barriers in terms of microstructure and charge collection losses.

II. Specific Properties of Organic Solar Cells There have been numerous reviews on the physics and chemistry of organic solar cells.19-29 Thus, we will here only briefly discuss some specific properties of organic solar cells that are of high relevance to the figures of merit that we will discuss in the following. Organic materials often allow quite high absorption coefficients at least in a certain spectral region30 but the typically low dielectric permittivities (εr ~ 3 to 4) ensure that the photogenerated 3 ACS Paragon Plus Environment


electron-hole pair is initially still a Coulombically bound exciton. Splitting this exciton is possible via introducing a network of two intimately mixed types of molecules. These molecules need to form a type II heterojunction as shown in Figure 1; i.e. one molecule needs to have both a higher electron affinity and a higher ionization potential than the other in order to allow injection of electrons from one molecule to the other but not of holes (or vice versa: injection of holes but not of electrons). The two molecules are usually called the donor and acceptor, with the donor injecting electrons into the acceptor molecule but also (for excitons photogenerated on the acceptor) the acceptor injecting holes into the donor. This donoracceptor blend - typically called a bulk heterojunction - allows ultrafast exciton separation with time constants on the order of hundreds of picoseconds or faster.31,32 Thus, photocurrent generation in organic solar cells can be quite efficient. However, the price that has to be paid is typically a reduction of the achievable open-circuit voltage (due to the energy level offsets at the heterojunction) and a reduction of mobilities33,34 in these blend systems relative to systems based on pure molecules used e.g. for transistor applications. Traditionally, the low mobilities and the voltage loss due to the donor-acceptor interface have been considered to be intrinsic problems of organic solar cells that impose a strong limit on the attainable solar cell efficiency. We will see in later parts of the article that low mobilities indeed remain a problem while the voltage loss at the heterojunction can be reduced to levels that are extremely low as compared to the situation a couple of years ago.

III. Thermodynamic Considerations Before we will focus on the specific figures of merit for organic solar cells, we will introduce the general thermodynamic limitations of single junction solar cells which is applicable to any type of solar cell independent of specific details of the absorber material. The specific

4 ACS Paragon Plus Environment

Page 4 of 46

Page 5 of 46 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


properties of organic solar cells will all lead to losses in photovoltage or photocurrent relative to the thermodynamic limit and will be discussed in sections IV and V. Solar cells are typically analyzed by studying the basic parameters extracted from current density-voltage (J-V) curves under illumination, namely efficiency η, open-circuit voltage Voc, short-circuit current density Jsc and fill factor FF. These can be compared for instance with the thermodynamic limits for the respective parameters, which follow from the Shockley-Queisser (SQ) theory35 or variations thereof if realistic absorptances,36-40 multijunction solar cells,41-43 multiple exciton generation,44,45 hot carrier effects46,47 or up- and down-conversion are taken into account.48,49 The classical SQ theory has the huge advantage that the device parameters would only depend on the temperature (usually kept constant at 300 K) and the band gap Eg of the solar cell. Any internal material properties, such as complex refractive index, mobility and lifetime are made redundant by assuming that every photon with energy above the band gap energy creates one electron-hole pair, which will be collected with 100% efficiency, and that the only relevant recombination mechanism controlling the open-circuit voltage would be radiative recombination as required by the principle of detailed balance.50 Under these assumptions, the equations for the saturation current density J0,SQ, the short-circuit current density Jsc,SQ and the open-circuit voltage Voc,SQ in the SQ limit become quite simple and are given by ∞

J 0,SQ = q ∫ φbb ( E , T = 300 K )dE ,

(1)

Eg

∞

J sc,SQ = q ∫ φsun ( E )dE ,

(2)

Eg

and

Voc,SQ =

 kT  J sc,SQ ln + 1 .  q  J 0,SQ 


(3)


Page 6 of 46

Here, we use the photon energy E, thermal energy kT, the AM1.5G solar spectrum φsun, used for the standardized testing of terrestrial solar cells,51 and the black body spectrum52 used for the radiation from the cell at room temperature

φbb ( E ) =

2πE 2 1 2πE 2 −E ≈ exp . 3 2 3 2 h c [exp(E / kT ) − 1] h c  kT 

(4)

Here, h is Planck’s constant and c is the speed of light. The current density-voltage curve under illumination in the SQ limit can be written as

  qV   J = J 0,SQ exp  − 1 − J sc,SQ .   kT  

(5)

In the SQ model and in any other case, the extracted power density P follows from the JV curve via P = -JV. The efficiency is then the ratio of the maximum electrical power density vs. the incoming power density, i.e.

η=∞

max(P )

.

(6)

∫ Eφ (E )dE sun

0

The efficiency η, the short-circuit current density Jsc and the open-circuit voltage Voc are three of the four main figures of merit used to compare photovoltaic performance. The fourth one, the fill factor FF, is not an independent parameter but follows from the other three via FF =

max( P) . J scVoc

(7)

The SQ model serves as a useful first reference to compare the actual performance of solar cells with different band gaps. Figure 2 compares experimental data of organic and inorganic solar cells with the Shockley-Queisser limit for (a) efficiency η, (b) open-circuit voltage Voc, (c) short-circuit current density Jsc and (d) fill factor FF. Both, Jsc and Voc are strongly band gap dependent in the SQ model, with Jsc increasing and Voc decreasing with decreasing band gap. Lower band gaps lead to a spectrally wider absorption range and thus a higher Jsc while lower band gaps also lead to exponentially higher saturation current densities as given by Eq.


Page 7 of 46 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(1). Because J0,SQ increases much more strongly with lower band gaps than Jsc,SQ the open circuit voltage decreases for lower band gap. The fill factor is weakly increasing with band gap. Thus, the efficiency in the SQ model has a maximum, which is however rather broad and leads to highest efficiencies at around 1.1 eV to 1.45 eV, where typical photovoltaic materials such as crystalline Si (c-Si), GaAs and CdTe can be found. Especially the GaAs and c-Si record cells are close to the SQ limit in Jsc, Voc and FF. In the case of c-Si, an additional intrinsic recombination process, namely Auger recombination,36,38,53,54 leads to slightly reduced VocsQ that currently limit efficiencies to about 26 %55,56 and therefore to slightly lower values than for GaAs solar cells (28.8 %).57 However, the set of organic solar data presented in Fig. 2 is substantially lower than the SQ limit in Jsc, Voc and FF and therefore, efficiencies substantially above 10% are still rare in organic photovoltaics. The blue shaded area in Figure 2 serves as a guide to the eye and its upper boundary is defined as 80% of Jsc,SQ, 85% of FFSQ and as Voc,SQ – 0.3 V, respectively. The upper boundary for the blue shaded for the efficiency is then calculated from the product η = FFJscVoc . While there are organic solar cells that are at the upper boundary or even beyond for either Jsc, Voc or FF, none comes even close in terms of efficiency, indicating that in organic photovoltaics photocurrent and photovoltage are not easily maximized in one and the same device even if the influence of the band gap is considered. Figure 3 provides a closer look at the spectrally-resolved losses in photocurrent and photovoltage by comparing two recently published organic solar cells7,17 with the SQ limit and a recent Pb-halide perovskite solar cell. All three devices are based on absorber materials with band gaps around 1.6 eV, which is therefore used for the calculation of the SQ limit. Figure 3a shows the external quantum efficiencies of the three cells and the step-function that is used in the SQ model. To assess the actual impact of the EQE on the cell’s efficiency figure 3b shows the product EQE(E )φsun (E ) of external quantum efficiency EQE and AM1.5G 7 ACS Paragon Plus Environment


Page 8 of 46

spectrum – and therefore the number of absorbed photons - that is used to calculate the shortcircuit current density in a general case via ∞

J sc = q ∫ EQE (E )φsun ( E )dE .

(8)

0

Comparison of figs. 3a and 3b show that a quantum efficiency < 1 has a substantially different impact on Jsc depending on the photon energy range where it appears due to the multiplication with the solar power density spectrum which is decaying strongly towards higher energies. Thus, contributions to the photocurrent are strongest for absorption close to the band edge of 1.6 eV. For instance, the low EQE of the PffBT4T-2DT:FBR solar cell below 2 eV leads to substantial losses in Jsc while the strong reduction in EQE for both organic solar cells above 2.5 eV is less of a concern. The perovskite solar cell comes already very close to the Shockley-Queisser limit mostly thanks to its extremely steep absorption onset. While a gradual absorption onset is also observed for several inorganic solar cells, dips and drops in the EQE at higher photon energies are more specific to organic solar cells where the absorption bands of the constituent materials are relatively narrow. Figure 3c shows the product FFVoc EQE(E )φsun (E ) , which integrated over energy gives the maximum electric power density and is therefore directly proportional to the efficiency η. The two organic solar cells are based on blends of polymers with non-fullerene acceptors and were chosen because of their high open-circuit voltages relative to their band gaps. For both devices, the open-circuit voltage exceeds 1 V, which is an excellent value when compared with other organic solar cells as seen in Fig. 2b. The same holds true for the perovskite solar cell with its high open-circuit voltage of 1.12 V.58 However, when studying Figure 3, it is clear that in relation to the SQ limit, the highest efficiency losses for the perovskite solar cell and the PTB7-Th:IDTBR:IDFBR cell are due to the last step, when the spectrally resolved photocurrent is converted into the spectrally resolved electric power density that is extracted from the cell. 8 ACS Paragon Plus Environment

Page 9 of 46 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 3 highlights a series of effects that have an impact on the efficiency and the efficiency limitations of organic solar cells that we will focus on in the following sections. In particular, we note that high open-circuit voltages can coincide with reduced EQE values, as seen for the case of the PffBT4T-2DT:FBR cell. In addition, it is possible to have strong absorption even in extremely thin organic films of about 100 nm thickness but not necessarily over the whole spectral range covered by inorganic semiconductors. This effect is seen in the PTB7-Th:IDTBR:IDFBR based solar cell. In addition, even for organic solar cells with high open-circuit voltages the product FF×Voc is substantially smaller than for instance for the perovskite solar cell with nearly the same band gap (see table I). In the following, we will first focus on the issue of the open-circuit voltage in general, the relation between the open-circuit voltage vs. photocurrent generation and then discuss figures of merit for charge transport.

IV.

Thermodynamic Limitations of the Open-Circuit Voltage

The open-circuit voltage of any real solar cell is reduced relative to the SQ limit given by Eq. (3) mostly due to (i) the effect of the solar cell quantum efficiency being different from the idealized step-function of the SQ limit and due to (ii) non-radiative recombination. A simple way of expressing these losses is via59  J J J kT  J sc  kT  J sc,SQ  = ln ln × sc × 0,SQ × 0,rad  q  J 0  q  J 0 ,SQ J sc,SQ J 0,rad J 0  . kT  J sc,SQ  kT  J 0 ,rad  kT  J 0  = Voc,SQ − ln − ln − ln q  J sc  q  J 0,SQ  q  J 0,rad 

Voc =

(9)

where the index ‘rad’ refers to quantities that are calculated using in analogy to the SQ method discussed above, however, taking the real quantum efficiency into account. The respective equation for the saturation current density J0,rad in the radiative limit is given by60,61



Page 10 of 46

∞

J 0,rad = q∫ EQE( E)φbb ( E)dE .

(10)

0

The integrand in Equation (10) specifies the photon flux emitted by pn-junction at equilibrium and J0,rad is the current that has to flow to make this emission possible. While Eq. (9) is not strictly valid62,63 in mostly or fully depleted solar cells like organic solar cells it is suitable for the purpose of studying voltage losses in organic solar cells.64 Based on Eq. (9), the difference between Voc,SQ and Voc can be expressed via three loss terms ( ∆VocSC , ∆Vocrad , ∆Vocnr ) that represent (from left to right in Eq. (9)) the loss in short circuit

current (Jsc1 V Open Circuit Voltages. Energ. Environ. Sci. 2016, 9, 3783-3793. (18) Hoke, E. T.; Vandewal, K.; Bartelt, J. A.; Mateker W. R.; Douglas, J. D.; Noriega, R.; Graham, K. R.; Frechet, J. M. J.; Salleo, A.; McGehee, M. D. Recombination in Polymer:Fullerene Solar Cells With Open-Circuit Voltages Approaching and Exceeding 1.0 V. Adv. Energy Mater. 2013, 3, 220-230. (19) Li, G.; Zhu, R.; Yang, Y. Polymer Solar Cells. Nat. Photon. 2012, 6, 153-161. (20) Credgington, D. Organic Photovoltaics. In Clean Electricity from Photovoltaics, Archer, M. D., Green, M. A., Eds.; Imperial College Press: London, 2015; pp 339-412. (21) Deibel, C.; Dyakonov, V.; Brabec, C. J. Organic Bulk-Heterojunction Solar Cells. Ieee J Sel Top Quant 2010, 16, 1517-1527. (22) Deibel, C.; Dyakonov, V. Polymer-Fullerene Bulk Heterojunction Solar Cells. Rep. Prog. Phys. 2010, 73, 096401. (23) Brabec, C. J.; Heeney, M.; McCulloch, I.; Nelson, J. Influence of Blend Microstructure on Bulk Heterojunction Organic Photovoltaic Performance. Chem. Soc. Rev. 2011, 40, 1185-1199. (24) Nelson, J. Polymer: Fullerene Bulk Heterojunction Solar Cells. Mater. Today 2011, 14, 462-470. (25) Forrest, S. R. The Limits to Organic Photovoltaic Cell Efficiency. MRS Bull. 2005, 30, 28-32. (26) Blom, P. W. M.; Mihailetchi, V. D.; Koster, L. J. A.; Markov, D. E. Device Physics of Polymer : Fullerene Bulk Heterojunction Solar Cells. Adv. Mater. 2007, 19, 1551-1566.



(27) Brabec, C. J.; Gowrisanker, S.; Halls, J. J. M.; Laird, D.; Jia, S. J.; Williams, S. P. Polymer-Fullerene Bulk-Heterojunction Solar Cells. Adv. Mater. 2010, 22, 3839-3856. (28) Clarke, T. M.; Durrant, J. R. Charge Photogeneration in Organic Solar Cells. Chem. Rev. 2010, 110, 6736-6767. (29) Menke, S. M.; Ran, N. A.; Bazan, G. C.; Friend, R. H. Understanding Energy Loss in Organic Solar Cells: Toward a New Efficiency Regime. Joule 2017. (30) Vezie, M. S.; Few, S.; Meager, I.; Pieridou, G.; Dörling, B.; Ashraf, R. S.; Go+¦i, A. R.; Bronstein, H.; McCulloch, I.; Hayes, S. C. et al. Exploring the Origin of High Optical Absorption in Conjugated Polymers. Nat. Mater. 2016, 15, 746. (31) Gelinas, S.; Rao, A.; Kumar, A.; Smith, S. L.; Chin, A. W.; Clark, J.; van der Poll, T. S.; Bazan, G. C.; Friend, R. H. Ultrafast Long-Range Charge Separation in Organic Semiconductor Photovoltaic Diodes. Science 2014, 343, 512. (32) Provencher, F.; Berube, N.; Parker, A. W.; Greetham, G. M.; Towrie, M.; Hellmann, C.; Cote, M.; Stingelin, N.; Silva, C.; Hayes, S. C. Direct Observation of Ultrafast LongRange Charge Separation at Polymer-Fullerene Heterojunctions. Nat. Commun. 2014, 5, 4288. (33) Proctor, C. M.; Love, J. A.; Nguyen, T. Q. Mobility Guidelines for High Fill Factor Solution-Processed Small Molecule Solar Cells. Adv. Mater. 2014, 26, 5957-5961. (34) von Hauff, E.; Dyakonov, V.; Parisi, J. Study of Field Effect Mobility in PCBM Films and P3HT:PCBM Blends. Sol. Energy Mater. Sol. Cells 2005, 87, 149-156. (35) Shockley, W.; Queisser, H. J. Detailed Balance Limit of Efficiency of Pn-Junction Solar Cells. J. Appl. Phys. 1961, 32, 510-519. (36) Tiedje, T.; Yablonovitch, E.; Cody, G. D.; Brooks, B. G. Limiting Efficiency of Silicon Solar-Cells. IEEE Trans. Elec. Dev. 1984, 31, 711-716. (37) Rau, U.; Werner, J. H. Radiative Efficiency Limits of Solar Cells With Lateral Band-Gap Fluctuations. Appl. Phys. Lett. 2004, 84, 3735-3737. (38) Green, M. A. Limits on the Open-Circuit Voltage and Efficiency of Silicon SolarCells Imposed by Intrinsic Auger Processes. IEEE Trans. Elec. Dev. 1984, 31, 671-678. (39) Kirchartz, T.; Taretto, K.; Rau, U. Efficiency Limits of Organic Bulk Heterojunction Solar Cells. J. Phys. Chem. C 2009, 113, 17958-17966. (40) Kirchartz, T.; Staub, F.; Rau, U. Impact of Photon Recycling on the Open-Circuit Voltage of Metal Halide Perovskite Solar Cells. ACS Energy Lett. 2016, 1, 731-739. (41) Henry, C. H. Limiting Efficiencies of Ideal Single and Multiple Energy-Gap Terrestrial Solar-Cells. J. Appl. Phys. 1980, 51, 4494-4500. (42) Araujo, G. L.; Marti, A. Absolute Limiting Efficiencies for Photovoltaic EnergyConversion. Sol. Energy Mater. Sol. Cells 1994, 33, 213-240. (43) Marti, A.; Araujo, G. L. Limiting Efficiencies for Photovoltaic Energy Conversion in Multigap Systems. Sol. Energy Mater. Sol. Cells 1996, 43, 203-222. 36 ACS Paragon Plus Environment

Page 36 of 46

Page 37 of 46 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(44) Werner, J. H.; Kolodinski, S.; Queisser, H. J. Novel Optimization Principles and Efficiency Limits for Semiconductor Solar-Cells. Phys. Rev. Lett. 1994, 72, 3851-3854. (45) Hanna, M. C.; Nozik, A. J. Solar Conversion Efficiency of Photovoltaic and Photoelectrolysis Cells With Carrier Multiplication Absorbers. J. Appl. Phys. 2006, 100. (46) Ross, R. T.; Nozik, A. J. Efficiency of Hot-Carrier Solar Energy Converters. J. Appl. Phys. 1982, 53, 3813-3818. (47) Würfel, P. Solar Energy Conversion With Hot Electrons From Impact Ionisation. Sol. Energy Mater. Sol. Cells 1997, 46, 43-52. (48) Trupke, T.; Green, M. A.; Würfel, P. Improving Solar Cell Efficiencies by DownConversion of High-Energy Photons. J. Appl. Phys. 2002, 92, 1668-1674. (49) Trupke, T.; Green, M. A.; Würfel, P. Improving Solar Cell Efficiencies by UpConversion of Sub-Band-Gap Light. J. Appl. Phys. 2002, 92, 4117-4122. (50) van Roosbroeck, W.; Shockley, W. Photon-Radiative Recombination of Electrons and Holes in Germanium. Phys. Rev. 1954, 94, 1558-1560. (51) Reference Solar Spectral Irradiance: Air Mass 1.5. American Society for Testing and Materials: NREL, Golden Colorado, 2017. (52) Planck, M. Vorlesungen ueber die Theorie der Waermestrahlung; Barth: Leipzig, 1906. (53) Richter, A.; Glunz, S. W.; Werner, F.; Schmidt, J.; Cuevas, A. Improved Quantitative Description of Auger Recombination in Crystalline Silicon. Phys. Rev. B 2012, 86, 165202. (54) Richter, A.; Hermle, M.; Glunz, S. W. Reassessment of the Limiting Efficiency for Crystalline Silicon Solar Cells. IEEE J. Photov. 2013, 3, 1184-1191. (55) Kaneka Internet Communication Sep 14, 2016. (56) Yoshikawa, K.; Kawasaki, H.; Yoshida, W.; Irie, T.; Konishi, K.; Nakano, K.; Uto, T.; Adachi, D.; Kanematsu, M.; Uzu, H. et al. Silicon Heterojunction Solar Cell With Interdigitated Back Contacts for a Photoconversion Efficiency Over 26%. Nat. Energy 2017, 2, 17032. (57) Green, M. A.; Emery, K.; Hishikawa, Y.; Warta, W.; Dunlop, E. D. Solar Cell Efficiency Tables (Version 47). Prog. Photovolt: Res. Appl. 2016, 24, 3-11. (58) Bi, D.; Tress, W.; Dar, M. I.; Gao, P.; Luo, J.; Renevier, C.; Schenk, K.; Abate, A.; Giordano, F.; Correa Baena, J. P. et al. Efficient Luminescent Solar Cells Based on Tailored Mixed-Cation Perovskites. Sci Adv 2016, 2, e1501170. (59) Rau, U.; Blank, B.; Müller, T. C. M.; Kirchartz, T. Efficiency Potential of Photovoltaic Materials and Devices Unveiled by Detailed-Balance Analysis. Phys. Rev. Applied 2017, 7, 044016.



(60) Kirchartz, T.; Rau, U.; Kurth, M.; Mattheis, J.; Werner, J. H. Comparative Study of Electroluminescence From Cu(In,Ga)Se-2 and Si Solar Cells. Thin Solid Films 2007, 515, 6238. (61) Rau, U. Reciprocity Relation Between Photovoltaic Quantum Efficiency and Electroluminescent Emission of Solar Cells. Phys. Rev. B 2007, 76, 085303. (62) Kirchartz, T.; Nelson, J.; Rau, U. Reciprocity Between Charge Injection and Extraction and Its Influence on the Interpretation of Electroluminescence Spectra in Organic Solar Cells. Phys. Rev. Applied 2016, 5, 054003. (63) Kirchartz, T.; Rau, U. Detailed Balance and Reciprocity in Solar Cells. Phys. Stat. Sol. A 2008, 205, 2737-2751. (64) Vandewal, K.; Tvingstedt, K.; Gadisa, A.; Inganas, O.; Manca, J. V. Relating the Open-Circuit Voltage to Interface Molecular Properties of Donor:Acceptor Bulk Heterojunction Solar Cells. Phys. Rev. B 2010, 81, 125204. (65) Ross, R. T. Some Thermodynamics of Photochemical Systems. J. Chem. Phys. 1967, 46, 4590-4593. (66) Blank, B.; Kirchartz, T.; Lany, S.; Rau, U. Selection Metric for Photovoltaic Materials Screening Based on Detailed-Balance Analysis. Phys. Rev. Applied 2017, 8, 024032. (67) Yao, J. Z.; Kirchartz, T.; Vezie, M. S.; Faist, M. A.; Gong, W.; He, Z. C.; Wu, H. B.; Troughton, J.; Watson, T.; Bryant, D. et al. Quantifying Losses in Open-Circuit Voltage in Solution-Processable Solar Cells. Phys. Rev. Applied 2015, 4, 014020. (68) Koster, L. J. A.; Shaheen, S. E.; Hummelen, J. C. Pathways to a New Efficiency Regime for Organic Solar Cells. Adv. Energy Mater. 2012, 2, 1246-1253. (69) Benduhn, J.; Tvingstedt, K.; Piersimoni, F.; Ullbrich, S.; Fan, Y.; Tropiano, M.; McGarry, K. A.; Zeika, O.; Riede, M. K.; Douglas, C. J. et al. Intrinsic Non-Radiative Voltage Losses in Fullerene-Based Organic Solar Cells. Nat. Energy 2017, 2, 17053. (70) Gould, I. R.; Noukakis, D.; Gomez-Jahn, L.; Young, R. H.; Goodman, J. L.; Farid, S. Radiative and Nonradiative Electron Transfer in Contact Radical-Ion Pairs. Chem. Phys. 1993, 176, 439-456. (71) Vandewal, K.; Ma, Z.; Bergqvist, J.; Tang, Z.; Wang, E.; Henriksson, P.; Tvingstedt, K.; Andersson, M. R.; Zhang, F.; Inganas, O. Quantification of Quantum Efficiency and Energy Losses in Low Bandgap Polymer:Fullerene Solar Cells With High Open-Circuit Voltage. Adv. Energy Mater. 2012, 22, 3480-3490. (72) Li, W. W.; Hendriks, K. H.; Furlan, A.; Wienk, M. M.; Janssen, R. A. J. High Quantum Efficiencies in Polymer Solar Cells at Energy Losses Below 0.6 EV. J. Am. Chem. Soc. 2015, 137, 2231-2234. (73) Nikolis, V. C.; Benduhn, J.; Holzmueller, F.; Piersimoni, F.; Lau, M.; Zeika, O.; Neher, D.; Koerner, C.; Spoltore, D.; Vandewal, K. Reducing Voltage Losses in Cascade Organic Solar Cells While Maintaining High External Quantum Efficiencies. Adv. Energy Mater. 1700855-1700n/a. 38 ACS Paragon Plus Environment

Page 38 of 46

Page 39 of 46 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(74) Bijleveld, J. C.; Zoombelt, A. P.; Mathijssen, S. G. J.; Wienk, M. M.; Turbiez, M.; de Leeuw, D. M.; Janssen, R. A. J. Poly(Diketopyrrolopyrrole-Terthiophene) for Ambipolar Logic and Photovoltaics. J. Am. Chem. Soc. 2009, 131, 16616. (75) Zhao, F.; Dai, S.; Wu, Y.; Zhang, Q.; Wang, J.; Jiang, L.; Ling, Q.; Wei, Z.; Ma, W.; You, W. et al. Single-Junction Binary-Blend Nonfullerene Polymer Solar Cells With 12.1% Efficiency. Adv. Mater. 2017, 29, 1700144-1700n/a. (76) Street, R. A. Luminescence and Recombination in Hydrogenated Amorphous Silicon. Advances in Physics 1981, 30, 593-676. (77) Street, R. A.; Biegelsen, D. K.; Weisfield, R. L. Recombination in a-Si: H: Transitions Through Defect States. Phys. Rev. B 1984, 30, 5861-5870. (78) Street, R. A. Hydrogenated amorphous silicon; Cambridge University Press: Cambridge, 1991. (79) Crandall, R. S. Transport in Hydrogenated Amorphous-Silicon P-I-N Solar-Cells. J. Appl. Phys. 1982, 53, 3350-3352. (80) Crandall, R. S. Modeling of Thin-Film Solar-Cells - Uniform-Field Approximation. J. Appl. Phys. 1983, 54, 7176-7186. (81) Crandall, R. S. Modeling of Thin-Film Solar-Cells - Nonuniform Field. J. Appl. Phys. 1984, 55, 4418-4425. (82) Kirchartz, T.; Nelson, J. Device Modelling of Organic Bulk Heterojunction Solar Cells. In Multiscale Modelling of Organic and Hybrid Photovoltaics, 352 ed.; Beljonne, D., Cornil, J., Eds.; Springer Berlin Heidelberg: 2014; pp 279-324. (83) Street, R. A.; Schoendorf, M.; Roy, A.; Lee, J. H. Interface State Recombination in Organic Solar Cells. Phys. Rev. B 2010, 81, 205307. (84) Street, R. A.; Krakaris, A.; Cowan, S. R. Recombination Through Different Types of Localized States in Organic Solar Cells. Adv. Funct. Mater. 2012, 22, 4608-4619. (85) Kirchartz, T.; Agostinelli, T.; Campoy-Quiles, M.; Gong, W.; Nelson, J. Understanding the Thickness-Dependent Performance of Organic Bulk Heterojunction Solar Cells: The Influence of Mobility, Lifetime and Space Charge. J. Phys. Chem. Lett. 2012, 3, 3470-3475. (86) Wetzelaer, G. J. A. H.; Kuik, M.; Blom, P. W. M. Identifying the Nature of Charge Recombination in Organic Solar Cells From Charge-Transfer State Electroluminescence. Adv. Energy Mater. 2012, 2, 1232-1237. (87) Kirchartz, T.; Deledalle, F.; Tuladhar, P. S.; Durrant, J. R.; Nelson, J. On the Differences Between Dark and Light Ideality Factor in Polymer:Fullerene Solar Cells. J. Phys. Chem. Lett. 2013, 4, 2371-2376. (88) Ridley, B. K. Quantum Processes in Semiconductors; Oxford University Press: Oxford, 2013.



(89) Markvart, T. Semiclassical Theory of Non-Radiative Transitions. Journal of Physics C: Solid State Physics 1981, 14, L895. (90) Markvart, T. Mulitphonon recombination. In Recombination in Semiconductors, Landsberg, P. T., Ed.; Cambridge University Press: Cambridge, 2003; pp 467-468. (91) Ridley, B. K. On the Multiphonon Capture Rate in Semiconductors. Solid State Electron 1978, 21, 1319-1323. (92) Bozyigit, D.; Yazdani, N.; Yarema, M.; Yarema, O.; Lin, W. M. M.; Volk, S.; Vuttivorakulchai, K.; Luisier, M.; Juranyi, F.; Wood, V. Soft Surfaces of Nanomaterials Enable Strong Phonon Interactions. Nature 2016, 531, 618-622. (93) Kirchartz, T.; Markvart, T.; Rau, U.; Egger, D. A. Impact of Small Phonon Energies on the Charge-Carrier Lifetimes in Metal-Halide Perovskites. J. Phys. Chem. Lett. 2018, 939946. (94) Dibb, G. F. A.; Kirchartz, T.; Credgington, D.; Durrant, J. R.; Nelson, J. Analysis of the Relationship Between Linearity of Corrected Photocurrent and the Order of Recombination in Organic Solar Cells. J. Phys. Chem. Lett. 2011, 2, 2407-2411. (95) Rauh, D.; Deibel, C.; Dyakonov, V. Charge Density Dependent Nongeminate Recombination in Organic Bulk Heterojunction Solar Cells. Adv. Funct. Mater. 2012, 22, 3371-3377. (96) Deibel, C.; Rauh, D.; Foertig, A. Order of Decay of Mobile Charge Carriers in P3HT:PCBM Solar Cells. Appl. Phys. Lett. 2013, 103, 043307. (97) Deledalle, F.; Tuladhar, P. S.; Nelson, J.; Durrant, J. R.; Kirchartz, T. Understanding the Apparent Charge Density Dependence of Mobility and Lifetime in Organic Bulk Heterojunction Solar Cells. J. Phys. Chem. C 2014, 118, 8837-8842. (98) Cowan, S. R.; Roy, A.; Heeger, A. J. Recombination in Polymer-Fullerene Bulk Heterojunction Solar Cells. Phys. Rev. B 2010, 82, 245207. (99) Bartesaghi, D.; Perez, I. d. C.; Kniepert, J.; Roland, S.; Turbiez, M.; Neher, D.; Koster, L. J. A. Competition Between Recombination and Extraction of Free Charges Determines the Fill Factor of Organic Solar Cells. Nat. Commun. 2015, 6, 7083. (100) Würfel, U.; Neher, D.; Spies, A.; Albrecht, S. Impact of Charge Transport on Current-Voltage Characteristics and Power-Conversion Efficiency of Organic Solar Cells. Nat. Commun. 2015, 6, 6951. (101) Kaienburg, P.; Rau, U.; Kirchartz, T. Extracting Information About the Electronic Quality of Organic Solar-Cell Absorbers From Fill Factor and Thickness. Phys. Rev. Applied 2016, 6, 024001. (102) Neher, D.; Kniepert, J.; Elimelech, A.; Koster, L. J. A. A New Figure of Merit for Organic Solar Cells With Transport-Limited Photocurrents. Sci. Rep. 2016, 6, 24861. (103) Shaheen, S. E.; Brabec, C. J.; Sariciftci, N. S.; Padinger, F.; Fromherz, T.; Hummelen, J. C. 2.5% Efficient Organic Plastic Solar Cells. Appl. Phys. Lett. 2001, 78, 841843. 40 ACS Paragon Plus Environment

Page 40 of 46

Page 41 of 46 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(104) Li, G.; Shrotriya, V.; Huang, J. S.; Yao, Y.; Moriarty, T.; Emery, K.; Yang, Y. HighEfficiency Solution Processable Polymer Photovoltaic Cells by Self-Organization of Polymer Blends. Nat. Mater. 2005, 4, 864-868. (105) Credgington, D.; Hamilton, R.; Atienzar, P.; Nelson, J.; Durrant, J. R. NonGeminate Recombination As the Primary Determinant of Open-Circuit Voltage in Polythiophene:Fullerene Blend Solar Cells: an Analysis of the Influence of Device Processing Conditions. Adv. Funct. Mater. 2011, 21, 2744-2753. (106) Park, S. H.; Roy, A.; Beaupre, S.; Cho, S.; Coates, N.; Moon, J. S.; Moses, D.; Leclerc, M.; Lee, K.; Heeger, A. J. Bulk Heterojunction Solar Cells With Internal Quantum Efficiency Approaching 100%. Nat. Photon. 2009, 3, 297-2U5. (107) He, Z. C.; Zhong, C. M.; Su, S. J.; Xu, M.; Wu, H. B.; Cao, Y. Enhanced PowerConversion Efficiency in Polymer Solar Cells Using an Inverted Device Structure. Nat. Photon. 2012, 6, 591-595. (108) Vohra, V.; Kawashima, K.; Kakara, T.; Koganezawa, T.; Osaka, I.; Takimiya, K.; Murata, H. Efficient Inverted Polymer Solar Cells Employing Favourable Molecular Orientation. 2015, 9, 403. (109) Zhang, G.; Zhang, K.; Yin, Q.; Jiang, X. F.; Wang, Z.; Xin, J.; Ma, W.; Yan, H.; Huang, F.; Cao, Y. High-Performance Ternary Organic Solar Cell Enabled by a Thick Active Layer Containing a Liquid Crystalline Small Molecule Donor. J. Am. Chem. Soc. 2017, 139, 2387-2395. (110) Guo, B.; Li, W.; Guo, X.; Meng, X.; Ma, W.; Zhang, M.; Li, Y. High Efficiency Nonfullerene Polymer Solar Cells With Thick Active Layer and Large Area. Adv. Mater. 2017, 29, 1702291-1702n/a. (111) Le Corre, V. M.; Chatri, A. R.; Doumon, N. Y.; Koster, L. J. A. Charge Carrier Extraction in Organic Solar Cells Governed by Steady-State Mobilities. Adv. Energy Mater. 2017, 7, 1701138-1701n/a. (112) Sandberg, O. J.; Sanden, S.; Sundqvist, A.; Smatt, J. H.; Österbacka, R. Determination of Surface Recombination Velocities at Contacts in Organic Semiconductor Devices Using Injected Carrier Reservoirs. Phys. Rev. Lett. 2017, 118, 076601. (113) Kiermasch, D.; Baumann, A.; Fischer, M.; Dyakonov, V.; Tvingstedt, K. Revisiting Lifetimes From Transient Electrical Characterization of Thin Film Solar Cells; a Capacitive Concern Evaluated for Silicon, Organic and Perovskite Devices. Energ. Environ. Sci. 2018. (114) Tvingstedt, K.; Gil-Escrig, L. n.; Momblona, C.; Rieder, P.; Kiermasch, D.; Sessolo, M.; Baumann, A.; Bolink, H. J.; Dyakonov, V. Removing Leakage and Surface Recombination in Planar Perovskite Solar Cells. ACS Energy Lett. 2017, 2, 424-430. (115) Zonno, I.; Martinez-Otero, A.; Hebig, J. C.; Kirchartz, T. Understanding MottSchottky Measurements Under Illumination in Organic Bulk Heterojunction Solar Cells. Phys. Rev. Applied 2017, 7, 034018.



(116) Torabi, S.; Cherry, M.; Duijnstee, E. A.; Le Corre, V. M.; Qiu, L.; Hummelen, J. C.; Palasantzas, G.; Koster, L. J. A. Rough Electrode Creates Excess Capacitance in Thin-Film Capacitors. ACS Appl. Mater. Interfaces 2017, 9, 27290-27297. (117) Lee, H. K. H.; Telford, A. M.; Rohr, J. A.; Wyatt, M. F.; Rice, B.; Wu, J.; de Castro Maciel, A.; Tuladhar, S. M.; Speller, E.; McGettrick, J. et al. The Role of Fullerenes in the Environmental Stability of Polymer:Fullerene Solar Cells. Energ. Environ. Sci. 2018. (118) Wetzelaer, G. A. H.; Blom, P. W. M. Ohmic Current in Organic Metal-InsulatorMetal Diodes Revisited. Phys. Rev. B 2014, 89, 241201. (119) de Bruyn, P.; van Rest, A. H. P.; Wetzelaer, G. A. H.; de Leeuw, D. M.; Blom, P. W. M. Diffusion-Limited Current in Organic Metal-Insulator-Metal Diodes. Phys. Rev. Lett. 2013, 111, 186801. (120) van Duren, J. K. J.; Yang, X.; Loos, J.; Bulle-Lieuwma, C. W. T.; Sieval, A. B.; Hummelen, J. C.; Janssen, R. A. J. Relating the Morphology of Poly(p-Phenylene Vinylene)/Methanofullerene Blends to Solar-Cell Performance. Adv. Funct. Mater. 2004, 14, 425-434. (121) Maturova, K.; van Bavel, S. S.; Wienk, M. M.; Janssen, R. A. J.; Kemerink, M. Description of the Morphology Dependent Charge Transport and Performance of Polymer:Fullerene Bulk Heterojunction Solar Cells. Adv. Funct. Mater. 2011, 21, 261-269. (122) Maturova, K.; van Bavel, S. S.; Wienk, M. M.; Janssen, R. A. J.; Kemerink, M. Morphological Device Model for Organic Bulk Heterojunction Solar Cells. Nano Lett. 2009, 9, 3032-3037. (123) Ye, L.; Hu, H.; Ghasemi, M.; Wang, T.; Collins, B. A.; Kim, J. H.; Jiang, K.; Carpenter, J. H.; Li, H.; Li, Z. et al. Quantitative Relations Between Interaction Parameter, Miscibility and Function in Organic Solar Cells. Nat. Mater. 2018. (124) Ye, L.; Collins, B. A.; Jiao, X.; Zhao, J.; Yan, H.; Ade, H. Miscibility-Function Relations in Organic Solar Cells: Significance of Optimal Miscibility in Relation to Percolation. Adv. Energy Mater. 2018, 1703058-1703n/a. (125) Baran, D.; Li, N.; Breton, A.-C.; Osvet, A.; Ameri, T.; Leclerc, M.; Brabec, C. J. Qualitative Analysis of Bulk-Heterojunction Solar Cells Without Device Fabrication: An Elegant and Contactless Method. J. Am. Chem. Soc. 2014, 136, 10949-10955. (126) Li, Y. X.; Liu, X. D.; Wu, F. P.; Zhou, Y.; Jiang, Z. Q.; Song, B.; Xia, Y. X.; Zhang, Z. G.; Gao, F.; Inganas, O. et al. Non-Fullerene Acceptor With Low Energy Loss and High External Quantum Efficiency: Towards High Performance Polymer Solar Cells. J. Mater. Chem. A 2016, 4, 5890-5897. (127) Liu, T.; Pan, X.; Meng, X.; Liu, Y.; Wei, D.; Ma, W.; Huo, L.; Sun, X.; Lee, T. H.; Huang, M. et al. Alkyl Side-Chain Engineering in Wide-Bandgap Copolymers Leading to Power Conversion Efficiencies Over 10%. Adv. Mater. 2017, 29, 1604251-1604n/a. (128) Liu, J.; Chen, S.; Qian, D.; Gautam, B.; Yang, G.; Zhao, J.; Bergqvist, J.; Zhang, F.; Ma, W.; Ade, H. et al. Fast Charge Separation in a Non-Fullerene Organic Solar Cell With a Small Driving Force. Nat. Energy 2016, 1, 16089. 42 ACS Paragon Plus Environment

Page 42 of 46

Page 43 of 46 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(129) Yang, L.; Zhang, S.; He, C.; Zhang, J.; Yao, H.; Yang, Y.; Zhang, Y.; Zhao, W.; Hou, J. New Wide Band Gap Donor for Efficient Fullerene-Free All-Small-Molecule Organic Solar Cells. J. Am. Chem. Soc. 2017, 139, 1958-1966. (130) Yao, H.; Ye, L.; Hou, J.; Jang, B.; Han, G.; Cui, Y.; Su, G. M.; Wang, C.; Gao, B.; Yu, R. et al. Achieving Highly Efficient Nonfullerene Organic Solar Cells With Improved Intermolecular Interaction and Open-Circuit Voltage. Adv. Mater. 2017, 29, 1700254-1700n/a. (131) Yao, H.; Cui, Y.; Yu, R.; Gao, B.; Zhang, H.; Hou, J. Design, Synthesis, and Photovoltaic Characterization of a Small Molecular Acceptor With an Ultra-Narrow Band Gap. Angew. Chem. Int. Ed. 2017, 56, 3045-3049. (132) Ye, L.; Zhao, W.; Li, S.; Mukherjee, S.; Carpenter, J. H.; Awartani, O.; Jiao, X.; Hou, J.; Ade, H. High-Efficiency Nonfullerene Organic Solar Cells: Critical Factors That Affect Complex Multi-Length Scale Morphology and Device Performance. Adv. Energy Mater. 2017, 7, 1602000-1602n/a. (133) Yuan, J.; Qiu, L.; Zhang, Z. G.; Li, Y.; Chen, Y.; Zou, Y. Tetrafluoroquinoxaline Based Polymers for Non-Fullerene Polymer Solar Cells With Efficiency Over 9%. Nano Energy 2016, 30, 312-320. (134) Zhang, G.; Yang, G.; Yan, H.; Kim, J. H.; Ade, H.; Wu, W.; Xu, X.; Duan, Y.; Peng, Q. Efficient Nonfullerene Polymer Solar Cells Enabled by a Novel Wide Bandgap Small Molecular Acceptor. Adv. Mater. 2017, 29, 1606054-1606n/a. (135) Bin, H.; Gao, L.; Zhang, Z. G.; Yang, Y.; Zhang, Y.; Zhang, C.; Chen, S.; Xue, L.; Yang, C.; Xiao, M. et al. 11.4% Efficiency Non-Fullerene Polymer Solar Cells With Trialkylsilyl Substituted 2D-Conjugated Polymer As Donor. Nat. Commun. 2016, 7, 13651. (136) Bin, H.; Yang, Y.; Zhang, Z. G.; Ye, L.; Ghasemi, M.; Chen, S.; Zhang, Y.; Zhang, C.; Sun, C.; Xue, L. et al. 9.73% Efficiency Nonfullerene All Organic Small Molecule Solar Cells With Absorption-Complementary Donor and Acceptor. J. Am. Chem. Soc. 2017, 139, 5085-5094. (137) Cheng, P.; Zhang, M.; Lau, T. K.; Wu, Y.; Jia, B.; Wang, J.; Yan, C.; Qin, M.; Lu, X.; Zhan, X. Realizing Small Energy Loss of 0.55 EV, High Open-Circuit Voltage >1 V and High Efficiency >10% in Fullerene-Free Polymer Solar Cells Via Energy Driver. Adv. Mater. 2017, 29, 1605216-1605n/a. (138) Kawashima, K.; Tamai, Y.; Ohkita, H.; Osaka, I.; Takimiya, K. High-Efficiency Polymer Solar Cells With Small Photon Energy Loss. Nat. Commun. 2015, 6. (139) Li, Z.; Jiang, K.; Yang, G.; Lai, J. Y. L.; Ma, T.; Zhao, J.; Ma, W.; Yan, H. Donor Polymer Design Enables Efficient Non-Fullerene Organic Solar Cells. Nat. Commun. 2016, 7, 13094. (140) Liu, D.; Yang, B.; Jang, B.; Xu, B.; Zhang, S.; He, C.; Woo, H. Y.; Hou, J. Molecular Design of a Wide-Band-Gap Conjugated Polymer for Efficient Fullerene-Free Polymer Solar Cells. Energ. Environ. Sci. 2017, 10, 546-551.



(141) Yang, D.; Sasabe, H.; Sano, T.; Kido, J. Low-Band-Gap Small Molecule for Efficient Organic Solar Cells With a Low Energy Loss Below 0.6 EV and a High OpenCircuit Voltage of Over 0.9 V. ACS Energy Lett. 2017, 2, 2021-2025. (142) Nguyen, T. L.; Choi, H.; Ko, S. J.; Uddin, M. A.; Walker, B.; Yum, S.; Jeong, J. E.; Yun, M. H.; Shin, T. J.; Hwang, S. et al. Semi-Crystalline Photovoltaic Polymers With Efficiency Exceeding 9% in a [Similar]300 Nm Thick Conventional Single-Cell Device. Energ. Environ. Sci. 2014, 7, 3040-3051.


Page 44 of 46

Page 45 of 46

TOC Graphic: 104

13

PffBT4T

efficiency η (%)

PNTz4T

electronic quality Q (cm1.6V-2s1.2)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


11

103

PTB7-Th:BTR:PCBM

P3HT

102

9

FTAZ:ITIC-Th1

PBDB-T:IT-M:BisPCBM

101

PBDB-T-SF:IT-4F

7

PCE10:IDTBR:IDFBR

5

PTB7 MDMO-PPV PCDTBT

100 4

6

8

10

12

14

energy level matching ηScharber (%)



Thomas Kirchartz is a professor of electrical engineering and information technology at the University Duisburg-Essen and the head of the department of analytics and simulation and the group of organic and hybrid solar cells at the Research Centre Jülich (Institute for Energy and Climate Research). Previously he was a Junior Research Fellow at Imperial College London. His research interests cover all aspects regarding the fundamental understanding of photovoltaic devices including their characterization and simulation. Pascal Kaienburg is a PhD student at the Research Centre Jülich (Institute for Energy and Climate Research: Photovoltaics). He previously received a Master’s degree in physics from RWTH Aachen University for his thesis on radio-frequency studies on graphene. His current work covers the evaluation of novel materials for photovoltaics via device simulations as well as the fabrication and characterization of solution-processed hybrid inorganic/polymer solar cells with the aim of identifying limitations to device performance.

Derya Baran received a Helmholtz Postdoctoral Fellowship in 2015 and pursued post-doctoral studies as a joint research associate at Imperial Collage London and Research Center Jülich. Since January 2017, she is an assistant professor of material science and engineering at King Abdullah University of Science and Technology (KAUST). Her current research focuses on the engineering of smart materials for energy conversion applications such as solar cells and thermoelectrics.


Page 46 of 46

Figures of Merit Guiding Research on Organic ... - ACS Publications

Recommend Documents