Variation in the Photocurrent Response Due to Different Emissive

Subscriber access provided by READING UNIV

Article

Variation in the Photocurrent Response Due to Different Emissive States in Methylammonium Lead Bromide Perovskites Qi Shi, Supriya Ghosh, Abdus Salam Sarkar, Pushpendra Kumar, Zhengjun Wang, Suman Kalyan Pal, Tõnu Pullerits, and Khadga Jung Karki J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.8b00542 • Publication Date (Web): 02 Feb 2018 Downloaded from http://pubs.acs.org on February 2, 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 free 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 accessible to all readers and 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 13 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

Variation in the Photocurrent Response Due to Different Emissive States in Methylammonium Lead Bromide Perovskites Qi Shi†,#, Supriya Ghosh‡,#, Abdus Salam Sarkar‡, Pushpendra Kumar†, Zhengjun Wang†, Suman Kalyan Pal‡*, Tõnu Pullerits†**, and Khadga J. Karki†*** †

The Division of Chemical Physics and NanoLund, Lund University, Box 124, 22100 Lund, Sweden

‡

School of Basic Sciences and Advanced Material Research Center, Indian Institute of Technology Mandi, Kamand, 175005 HP, India AUTHOR INFORMATION Corresponding Authors * [email protected]

+91 1905 2670062

** [email protected]

+46 46 222 81 31

*** [email protected]

+46 46 222 83 40

Author Contributions #

Q.S. and S.G. contributed equally.

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

Abstract Thin films and crystals of methylammonium lead bromide (MAPbBr3) perovskites have strong photoluminescence (PL). Previous studies have shown that the emission arises from different states. However, the role of these states in the performance of a solar cell has not been reported. We have used photocurrent and photoluminescence microscopy (PCM and PLM) to investigate the correlation between the photocurrent (PC) and photoluminescence (PL) behavior in different regions of MAPbBr3 thin film solar cells. Our results show that the PC and the PL response from the different regions in the thin film show poor correlation compared to a high efficiency GaAs solar cell. Furthermore, we establish a relationship between the different emissive states and the PC and PL response. Out of the two emissive states at 2.34 eV and 2.28 eV, which have been reported, only the state at 2.34 eV has dominant contribution to the PC. Our results suggest that the emission at 2.28 eV is related to traps, which can lower the performance of the solar cells. Finally, the correlation analysis of the PC and the PL response we have presented can be used in any solar cell made from direct band gap semiconductor to identify the loss channels in the device.


Page 2 of 13

Page 3 of 13 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 Introduction Metal halide perovskites have emerged as excellent materials for photovoltaic technology due to ease of fabrication as well as favourable properties, such as high absorption coefficient1-5 and carrier mobilities6-10. The most efficient perovskite solar cells have power conversion efficiency (PCE) of 22.1%

11,12

. Although the solution processed perovskites are inherently

inhomogeneous, they are still highly emissive13-16. The high PCE as well as the PL yield suggests that the perovskite solar cells may be operating close to the Shockley-Queisser limit17. However, the high degree of correlation between the PC and PL yield in efficient solar cells made out of direct band gap materials, such as GaAs, is achieved only in the samples that have extremely low defect density. As the solution processed perovskite solar cells have high density of defects18,19 one does not expect high PC as well as PL from them. Thus, the role of heterogeneity and defects in the photovoltaic performance of the perovskite solar is being actively investigated20-25. It has been shown that the structural inhomogeneity affects the PL yield and spectra in MAPbBr3. At least two different kinds of emissions at energies of about 2.28 eV and 2.34 eV have been identified at different regions of MAPbBr3 crystals and thin films21,22,26,27. Although the impact of heterogeneity on the carrier lifetimes and photocurrent response have been studied previously20, 24, 28-38, the role of the different emissive states on the yield of PC has not been systematically investigated. Here, we have used PCM, and PLM to simultaneously measure the PC and PL from different regions in a MAPbBr3 thin film solar cell. PCM and PLM allow us to correlate PC and PL from the different emissive states. Our results show that the major contribution to the PC is from the emissive state at 2.34 eV, while the other emissive state at 2.28 eV does not show a clear contribution. We have also used PCM and PLM to investigate the correlation between the PC and PL from GaAs, which shows similar behavior with the PC response from the state at 2.34 eV in MAPbBr3 thin film. Our results also indicate that the state at 2.28 eV is populated by energy transfer from the state at 2.34 eV. Therefore, although its presence helps to increase the PL, it decreases the yield of the PC.

2 Experimental Methods 2.1 Device fabrication 3 ACS Paragon Plus Environment


Fluorine-doped tin oxide (FTO) coated glass substrate with sheet resistivity 7 Ωm was purchased from Sigma Aldrich, USA. The substrates were etched with zinc powder (Merck, USA) and 2 M HCl for the intended electrode pattern (2 mm × 25 mm, W × L). Patterned substrates were sequentially cleaned in detergent (5% labolene solution), de-ionized water, acetone, isopropyl alcohol (IPA) and ethanol for 20 minutes each in an ultrasonic bath. Cleaned substrates were treated with UV-ozone for 15 min to remove organic residuals. To prepare the TiO2 layer, PMT-20, received from Dyesol (Australia), was spin coated at 3000 rpm for 60 s. Then the TiO2 coated substrates were sintered at 500 oC for 60 min with heating ramp rate of 10oC/min. The MAPbBr3 layer on the top of FTO/TiO2 was then coated by the spin casting at 3000 rpm for 200 s and annealed on a hotplate at 100 oC for 2 min (inside the glove box). To deposit the hole transporting layer, poly (3-hexylthiophene 2-5,diyl) (P3HT) (Sigma Aldrich) was spin coated on FTO/TiO2/MAPbBr3 substrate at 3000 rpm for 30 s by using a concentration of 15 mg P3HT in 1ml toluene. Finally, the gold back contact was deposited by thermal evaporation under the pressure of 2 × 10-6. The active area was 0.02 cm2. GaAs p-i-n diode was obtained from Kyosemi Co. (part nr. KPDG008). The diode has an active area of 80 µm X 80 µm. The external quantum efficiency of the device is about 78% at 790 nm. The J-V curve of the device illuminated by the laser is given in the Supplementary Information. 2.2 Electrical characterization All the devices were characterized in ambient condition. The photovoltaic current-voltage measurements were carried out on an OAI solar simulator (USA), composed of Keithley 2400 source measure unit. Solar irradiation was simulated using a class AAA solar simulator (OAI Trisol) fitted with AM1.5 (air mass) filter and calibrated by a standard Si solar cell. 2.3 Optical setup and data acquisition The optical setup has been described elsewhere39-41. In brief, a pulsed laser beam from a mode locked Ti:sapphire oscillator (Synergy, Femtolasers) was used as the light source (see the supplementary information for the schematics of the setup). The beam was split into two using a 50:50 beam splitter. The phase of each of the beams was modulated by using acoustooptic modulators such that the difference in the modulation frequency was set to 3 kHz. The two beams were collimated collinearly by using a second beam splitter. One of the outputs of from the second beam splitter was sent to an inverted microscope (Nikon Ti-S) for the excitation of the solar cell. The intensity of the two photon absorption induced PL was 4 ACS Paragon Plus Environment

Page 4 of 13

Page 5 of 13 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


detected by an avalanche photodiode. Two-photon excitation was used mainly to reduce the emission due to scattered light as well as to reduce the excitation induced effects that are commonly observed in perovskites21. The quadratic dependence of the PC and the PL response on the excitation intensity (shown in the Supplementary Information) confirms that the signals arise from two-photon excitation. The PC response was amplified by a preamplifier (SR570, Stanford Research Systems). The intensity of the PL and PC modulated at 3 kHz, which contains only the light induced PL and PC rather than the dark current induced signals, was analyzed by using generalized lock-in amplifier42,43. The PC and PL response at the different positions in the sample were obtained by raster scanning the laser focus using a piezo-driven scanner (Nano-LP Series, Mad City Labs). The PL spectra were recorded by a spectrometer (Flame, Ocean Optics).

3 Results and Discussion

Figure 1. (a) Diagram of perovskite cell architecture employed consisting of indium tin oxide (ITO)/ fluorine doped tin oxide (FTO)/ titanium dioxide (TiO2)/ perovskite/ Poly (3hexylthiophene-2,5-diyl) (P3HT)/ Gold (Au). (b) Energy level alignment of the fabricated devices. (c) Photocurrent density-voltage (J-V) curves of MAPbBr3 perovskite solar cells with P3HT hole conductor. (d) Scanning electron microscope (SEM) image of MAPbBr3 perovskite solar cells 5 ACS Paragon Plus Environment


The architecture of the thin film solar cell device, energy level alignment and the photocurrent density-voltage (J-V) curves of MAPbBr3 perovskite solar cells are illustrated in Figures 1a, b and c, respectively. As shown in Figure 1a, the device consists of a transparent conductive electrode and a thin TiO2 layer followed by perovskite (MAPbBr3) and a hole transporting layer (P3HT). The back contact is a thin layer of thermally evaporated metal (gold) electrode. As shown in the band alignment of the fabricated device (Figure 1b), the MAPbBr3 can inject the electron to the TiO2 layer and holes to the hole transporting material (P3HT). The injected electrons and holes are then transported and collected by the transparent conductive electrode and the metal electrode. Figure 1c depicts the measured current density versus voltage (J-V) characteristics of the fabricated device under illumination with different intensity of light. The device exhibits a short circuit current density of 6.18 mA/cm2, open circuit voltage of 0.81 V, and a fill factor of 41.07%, yielding a power conversion efficiency of 2.07% (under 100 mW/cm2). Figure 1d shows the Scanning electron microscope (SEM) image of MAPbBr3 perovskite solar cells. We can observe a heterogeneous distribution of grains with median grain size ~80 µm, which is larger compared to the spatial resolution of this techniques 1 µm. The measurement of PC and PL are done over an area of 20 µm X 20 µm in the thin film.

Figure 2. (a) PC map and (b) PL map measured on the film of GaAs solar cell, and (c) PC map with region A marked by a red box and (d) PL map with region B marked by a blue box measured on the film of MAPbBr3 perovskite.


Page 6 of 13

Page 7 of 13 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


In order to investigate the relation between PC and PL in an ideal solar cell, we first analyze the PCM and PLM of GaAs solar cell at zero bias shown in Figure 2a and 2b, respectively. The figures show an edge of the solar cell with the high PC and PL from the active region (yellow) and no PC or PL from the substrate (blue). As can be seen in the figures, the regions that give high PC also give high PL. We calculate the Pearson’s correlation coefficient (r)44 of the two images using equation (1):

∑ ̅

( 1),

∑ ̅ ∑

where xi and yi denote the PC and PL yields at different positions in the images, respectively. The correlation coefficient calculated from the two images is 0.9993. Such a high degree of correlation points to the fact that the states that contribute to the PC also contribute to the PL, which is expected in the case of the GaAs solar cell. The PCM and PLM of MAPbBr3, on the other hand, do not show a clear correlation. The Pearson’s correlation coefficient of the PC and the PL maps in Figure 2c and 2d is only 0.32. Moreover, the entire MAPbBr3 perovskite solar cell does not show homogeneous response. Although inhomogeneity in the film thickness may account for some of the variation observed in the PC and PL, it does not explain the lack of correlation. Contact heterogeneity proposed by Eperon GE et al. adds randomness to the PC and PL response 24, which can explain the lack of correlation. However, the intrinsic difference in the PC and PL yield from the different states in MAPbBr3 can also result in the poor correlation.

Figure 3. PL spectrum peak fitting results as a function of photocurrent response for positions of interest (show in supplementary Table S1) in MAPbBr3 perovskite solar cell. (a) The PL spectrum is fitted with two Voigt profiles centered at 2.34 eV (blue line) and 2.28 eV (red line); (b) PL and PC correlation in regions where the 2.28 eV emission does not occur; (c) PL and PC correlation in regions shows that there is an energy transfer from 2.34 eV to 2.28 eV. The blue and the red dots are the areas under the corresponding Voigt profiles in (a).



In order to explore the intrinsic difference of the PC and PL response of the two emissive states in perovskite solar cell, we have measured the PL spectra at each point in the image of Figure 2d at zero bias voltage. One of the representative spectra is shown in Figure 3a. The spectrum is fitted with two Voigt profiles centered at 2.34 eV (marked as blue) and 2.28 eV (marked as red). The area under the two profiles gives the corresponding PL intensity, (in Figure 3a). The decomposition of the PL spectra into two components allows us to investigate the differences in the PC response from the two emissive states. We select positions with high PC in the PCM or high PL in the PLM according to figure 2. The coordinates of those positions are shown in Table S1 of the supplementary information. In general, one expects four pathways by which the excited carriers can relax--- two pathways each corresponding to the PC and PL from the two states at 2.34 eV and 2.28 eV. In all of the selected positions in the sample, we can observe the PL at 2.34 eV, but the emission at 2.28 eV does not occur everywhere. In Figure 3b, we show the PL contribution at 2.34 eV vs the PC at the positions where the emission at 2.28 eV is not present. The figure also shows that at a number of positions in the image, we obtain significant PL even when the corresponding PC is negligible. We attribute this to the poor contacts of the electrodes. In these positions the carriers can only relax by radiative and nonradiative recombination. Moreover, the lack of PL component at 2.28 eV means that the corresponding states are not present there suggesting that the PC at these positions mainly originates from the states which are emitting at 2.34 eV. Figure 3c shows the PL yields vs. PC from the positions where the contribution from the state at 2.28 eV is significant. The PL yields are randomly distributed, which again suggests heterogeneity in the contacts. Although the presence of both the PL components may be taken as the evidence of the PC response from both of the emissive states, it could be misleading. The distribution seen in Figure 3c can also appear if only the state at 2.34 eV contributes to the PC provided that it also can populate the state at 2.28 eV via energy transfer. Previous studies have shown evidence of such energy transfer processes21, 26. In order to test if the state at 2.28 eV contributes to the PC, we have carried out further correlation analysis between the PC and PL by varying the external bias.


Page 8 of 13

Page 9 of 13 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 4. (a) PC-PL relation in the region A with emissive state at 2.28 eV by applying different forward bias to MAPbBr3 perovskite solar cell; (b) in the region B without the emissive state at 2.28 eV and (c) PC-PL relationship obtained by applying different forward bias to the GaAs solar cell; We have selected two positions in the sample to investigate the changes in the yield of the PL and PC at different bias voltage. In one of the positions, we call it A, (in Figure 4a) we only have PL at 2.34 eV while in the other position, we call it B, we have significant PL from the state at 2.28 eV (Figure 4b). A forward bias is varied from 0 to 0.25 V. As we use signal at 3 kHz rather than the normal DC current, it is important to make sure that the bias does not influence the impedance of the device. Therefore, we have used a small window of bias voltage (0 to 0.25 V). We have also measured the yield of PC and PL from the GaAs solar cell under similar bias conditions (Figure 4c). Typically, when forward bias is applied to a direct band gap solar cell, fewer photogenerated carriers are extracted as current and more carriers recombine radiatively17, which leads to a negative correlation between the PC and the PL. In our experiment, we have used intensity modulated light field to excite the sample. The PC and the PL signals are detected at the modulation frequency (see Experimental methods) in order to select only the contributions from the light induced current. In comparison, the DC signals contain a rather large contribution from the dark current that cannot be easily separated from the signal due to photogenerated carriers. The correlation coefficient between the PC and the PL signals obtained by varying the bias in GaAs solar cell (Figure 4c) and region A of the perovskite sample (Figure 4a) is -0.97. On the other hand, the PC-PL correlation coefficient in the region B is only -0.4. Although, the coefficient is not zero, the weak correlation between the PC and the PL signals indicates that the state at 2.28 eV does not significantly contribute to the PC. Among the two emissions, the emission at 2.34 eV is close to the band gap of MAPbBr3 (about 2.36 eV)22, hence it can be assigned to the radiative band-to-band carrier 9 ACS Paragon Plus Environment


recombination. The emission at 2.28 eV is significantly smaller than the band gap energy. Its origin has been debated to be either PL from different phase of the material or defect related polaronic emission. Although the variation of the yield of PC with the phase has not been reported, it is unlikely to differ significantly such that the correlation between the signals is suppressed. On the other hand, the carriers trapped in the defects do not contribute to the PC. Thus our results suggest that the emission at 2.28 eV is due to the emission from the trapped carriers. The presence of the defects that emit but do not contribute to PC clearly indicates that high PL from the perovskite solar cell does not necessarily indicate high PCE. It is important to note that the emission at 2.28 eV is absent in some regions of the solar cells (Figure 3b), which suggests that sample preparation may be optimized to reduce the emissive traps in order to increase the PCE.

4 Conclusions In summary, we have presented a methodological analysis based on the PCM and PLM of MAPbBr3 perovskite solar cell and GaAs solar cell to investigate the variation in the PC response from the emissive states at 2.28 eV and 2.34 eV. Our results show significant inhomogeneity in the PC and the PL from the MAPbBr3 perovskite solar cells compared with the GaAs solar cell. We observe a strong correlation between the PC and PL signals from GaAs, which contrasts with the weak correlation in MAPbBr3. Our results further indicate that only the state at 2.34 eV has significant contribution to the PC, while the presence of the emissive state at 2.28 eV may lower the performance of the solar cell.

Supporting Information The supporting information contains the following: S1. Optical setup S2. Details of the positions of interest S3. Excitation dependent PL and PC of MAPbBr3 perovskite solar cell S4. Current density versus voltage (J-V) characteristics of GaAs solar cell

Acknowledgements Financial support from the Swedish Research Council, the Crafoord Foundation, NanoLund, Knut, Alice Wallenberg Foundation and the DST (Grant No. DST/INT/SWD/VR/P-06/2014)


Page 10 of 13

Page 11 of 13 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


under Indo-Swedish (DST-VR) joint scheme is gratefully acknowledged. SG, ASS and SKP are highly thankful to IIT Mandi and AMRC (Advanced Material Research Centre) for providing research facilities. QS and ZW are grateful to China Scholarship Council (CSC) for the financial support.

References (1) Hodes, G. Perovskite-based solar cells. Science 2013, 342, 317-318. (2) Lee, M. M.; Teuscher, J.; Miyasaka, T.; Murakami, T. N.; Snaith, H. J. Efficient hybrid solar cells based on meso-superstructured organometal halide perovskites. Science 2012, 338, 643-647. (3) Kim, H.-S.; Lee, C.-R.; Im, J.-H.; Lee, K.-B.; Moehl, T.; Marchioro, A.; Moon, S.-J.; Humphry-Baker, R.; Yum, J.-H.; Moser, J. E. Lead iodide perovskite sensitized all-solid-state submicron thin film mesoscopic solar cell with efficiency exceeding 9%. Sci. Rep 2012, 2,591. (4) Yamada, Y.; Nakamura, T.; Endo, M.; Wakamiya, A.; Kanemitsu, Y. Near-band-edge optical responses of solution-processed organic–inorganic hybrid perovskite CH3NH3PbI3 on mesoporous TiO2 electrodes. App. Phys. Express 2014, 7, 032302. (5) Deschler, F.; Price, M.; Pathak, S.; Klintberg, L. E.; Jarausch, D.-D.; Higler, R.; Hüttner, S.; Leijtens, T.; Stranks, S. D.; Snaith, H. J. High photoluminescence efficiency and optically pumped lasing in solution-processed mixed halide perovskite semiconductors. J. Phys. Chem. Lett. 2014, 5, 1421-1426. (6) Stranks, S. D.; Eperon, G. E.; Grancini, G.; Menelaou, C.; Alcocer, M. J.; Leijtens, T.; Herz, L. M.; Petrozza, A.; Snaith, H. J. Electron-hole diffusion lengths exceeding 1 micrometer in an organometal trihalide perovskite absorber. Science 2013, 342, 341-344. (7) Xing, G.; Mathews, N.; Sun, S.; Lim, S. S.; Lam, Y. M.; Grätzel, M.; Mhaisalkar, S.; Sum, T. C. Long-range balanced electron-and hole-transport lengths in organic-inorganic CH3NH3PbI3. Science 2013, 342, 344-347. (8) Wehrenfennig, C.; Eperon, G. E.; Johnston, M. B.; Snaith, H. J.; Herz, L. M. High charge carrier mobilities and lifetimes in organolead trihalide perovskites. Adv. Mater. 2014, 26, 1584-1589. (9) Guo, Z.; Manser, J. S.; Wan, Y.; Kamat, P. V.; Huang, L. Spatial and temporal imaging of long-range charge transport in perovskite thin films by ultrafast microscopy. Nat. Commun. 2015, 6, 7471. (10) Zheng, K.; Abdellah, M.; Zhu, Q.; Kong, Q.; Jennings, G.; Kurtz, C. A.; Messing, M. E.; Niu, Y.; Gosztola, D. J.; Al-Marri, M. J. Direct experimental evidence for photoinduced strong-coupling polarons in organolead halide perovskite nanoparticles. J. Phys. Chem. Lett. 2016, 7, 4535-4539. (11) Kojima, A.; Teshima, K.; Shirai, Y.; Miyasaka, T. Organometal halide perovskites as visible-light sensitizers for photovoltaic cells. J. Am. Chem. Soc. 2009, 131, 6050-6051. (12) Burschka, J.; Pellet, N.; Moon, S.-J.; Humphry-Baker, R.; Gao, P.; Nazeeruddin, M. K.; Grätzel, M. Sequential deposition as a route to high-performance perovskite-sensitized solar cells. Nature 2013, 499, 316-319. (13) Tan, Z.-K.; Moghaddam, R. S.; Lai, M. L.; Docampo, P.; Higler, R.; Deschler, F.; Price, M.; Sadhanala, A.; Pazos, L. M.; Credgington, D. Bright light-emitting diodes based on organometal halide perovskite. Nat. Nanotechnol. 2014, 9, 687-692. (14) Cho, H.; Jeong, S.-H.; Park, M.-H.; Kim, Y.-H.; Wolf, C.; Lee, C.-L.; Heo, J. H.; Sadhanala, A.; Myoung, N.; Yoo, S. Overcoming the electroluminescence efficiency limitations of perovskite light-emitting diodes. Science 2015, 350, 1222-1225. 11 ACS Paragon Plus Environment


(15) Hoye, R. L.; Chua, M. R.; Musselman, K. P.; Li, G.; Lai, M. L.; Tan, Z. K.; Greenham, N. C.; MacManus‐Driscoll, J. L.; Friend, R. H.; Credgington, D. Enhanced performance in fluorene‐free organometal halide perovskite light‐emitting diodes using tunable, low electron affinity oxide electron injectors. Adv. Mater. 2015, 27, 1414-1419. (16) Song, J.; Li, J.; Li, X.; Xu, L.; Dong, Y.; Zeng, H. Quantum dot light‐emitting diodes based on inorganic perovskite cesium lead halides (CsPbX3). Adv. Mater. 2015, 27, 71627167. (17) Miller, O. D.; Yablonovitch, E.; Kurtz, S. R. Strong internal and external luminescence as solar cells approach the Shockley–Queisser limit. IEEE . Photovolt. 2012, 2, 303-311. (18) Miyano, K.; Tripathi, N.; Yanagida, M.; Shirai, Y. Lead halide perovskite photovoltaic as a model p–i–n diode. Acc. Chem. Res. 2016, 49, 303-310. (19) Zuo, Z.; Ding, J.; Zhao, Y.; Du, S.; Li, Y.; Zhan, X.; Cui, H. Enhanced optoelectronic performance on the (110) lattice plane of an MAPbBr3 single crystal. J. Phys. Chem. Lett. 2017, 8, 684-689. (20) Vorpahl, S. M.; Stranks, S. D.; Nagaoka, H.; Eperon, G. E.; Ziffer, M. E.; Snaith, H. J.; Ginger, D. S. Impact of microstructure on local carrier lifetime in perovskite solar cells. Science 2015, 348, 683–686. (21) Ghosh, S.; Pal, S. K.; Karki, K. J.; Pullerits, T. n. Ion migration heals trapping centers in CH3NH3PbBr3 perovskite. ACS Energy Lett. 2017, 2, 2133-2139. (22) Dar, M. I.; Jacopin, G.; Meloni, S.; Mattoni, A.; Arora, N.; Boziki, A.; Zakeeruddin, S. M.; Rothlisberger, U.; Grätzel, M. Origin of unusual bandgap shift and dual emission in organic-inorganic lead halide perovskites. Sci. Adv. 2016, 2, e1601156. (23) Zhao, Z.; Chen, X.; Wu, H.; Wu, X.; Cao, G. Probing the photovoltage and photocurrent in perovskite solar cells with nanoscale resolution. Adv. Funct. Mater. 2016, 26, 3048-3058. (24) Eperon, G. E.; Moerman, D.; Ginger, D. S. Anticorrelation between local photoluminescence and photocurrent suggests variability in contact to active layer in perovskite solar cells. ACS Nano 2016, 10, 10258-10266. (25) Wen, X.; Sheng, R.; Ho-Baillie, A. W.; Benda, A.; Woo, S.; Ma, Q.; Huang, S.; Green, M. A. Morphology and carrier extraction study of organic–inorganic metal halide perovskite by one-and two-photon fluorescence microscopy. J. Phys. Chem. Lett. 2014, 5, 3849-3853. (26) Guo, D.; Bartesaghi, D.; Wei, H.; Hutter, E. M.; Huang, J.; Savenije, T. J. Photoluminescence from radiative surface states and excitons in methylammonium lead bromide perovskites. J. Phys. Chem. Lett. 2017, 8, 4258-4263. (27) Dar, M. I.; Hinderhofer, A.; Jacopin, G.; Belova, V.; Arora, N.; Zakeeruddin, S. M.; Schreiber, F.; Grätzel, M. Function follows form: correlation between the growth and local emission of perovskite structures and the performance of solar cells. Adv. Funct. Mater. 2017, 27, 1701433. (28) Ostrowski, D. P.; Glaz, M. S.; Goodfellow, B. W.; Akhavan, V. A.; Panthani, M. G.; Korgel, B. A.; Vanden Bout, D. A. Mapping spatial heterogeneity in Cu (In1− xGax) Se2 nanocrystal‐based photovoltaics with scanning photocurrent and fluorescence microscopy. Small 2010, 6, 2832-2836. (29) Qiu, W.; Hu, W. Laser beam induced current microscopy and photocurrent mapping for junction characterization of infrared photodetectors. Sci. China. Phys. Mech. Astron. 2015, 58, 1-13. (30) Brenner, T. J.; McNeill, C. R. Spatially resolved spectroscopic mapping of photocurrent and photoluminescence in polymer blend photovoltaic devices. J. Phys. Chem. C 2011, 115, 19364-19370. (31) Song, Z.; Abate, A.; Watthage, S. C.; Liyanage, G. K.; Phillips, A. B.; Steiner, U.; Graetzel, M.; Heben, M. J. In-situ observation of moisture-induced degradation of perovskite


Page 12 of 13

Page 13 of 13 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


solar cells using laser-beam induced current. Photovoltaic Specialists Conference (PVSC), 2016 IEEE 43rd, IEEE: 2016; pp 1202-1206. (32) Rau, U.; Grabitz, P.; Werner, J. Resistive limitations to spatially inhomogeneous electronic losses in solar cells. Appl. Phys. Lett. 2004, 85, 6010-6012. (33) Shockley, W.; Queisser, H. J. Detailed balance limit of efficiency of p‐n junction solar cells. J. Appl. Phys. 1961, 32, 510-519. (34) Zhang, W.; Burlakov, V. M.; Graham, D. J.; Leijtens, T.; Osherov, A.; Bulović, V.; Snaith, H. J.; Ginger, D. S.; Stranks, S. D. Photo-induced halide redistribution in organic– inorganic perovskite films. Nat. Commun. 2016, 7,11683. (35) Mosconi, E.; Meggiolaro, D.; Snaith, H. J.; Stranks, S. D.; De Angelis, F. Light-induced annihilation of Frenkel defects in organo-lead halide perovskites. Energy Environ. Sci. 2016, 9, 3180-3187. (36) Tian, Y.; Peter, M.; Unger, E.; Abdellah, M.; Zheng, K.; Pullerits, T.; Yartsev, A.; Sundström, V.; Scheblykin, I. G. Mechanistic insights into perovskite photoluminescence enhancement: light curing with oxygen can boost yield thousandfold. Phys. Chem. Chem. Phys. 2015, 17, 24978-24987. (37) Noel, N. K.; Abate, A.; Stranks, S. D.; Parrott, E. S.; Burlakov, V. M.; Goriely, A.; Snaith, H. J. Enhanced photoluminescence and solar cell performance via lewis base passivation of organic–inorganic lead halide perovskites. ACS Nano 2014, 8, 9815-9821. (38) Yamada, Y.; Endo, M.; Wakamiya, A.; Kanemitsu, Y. Spontaneous defect annihilation in CH3NH3PbI3 thin films at room temperature revealed by time-resolved photoluminescence spectroscopy. J. Phys. Chem. Lett. 2015, 6, 482-486. (39) Osipov, V. A.; Shang, X.; Hansen, T.; Pullerits, T.; Karki, K. J. Nature of relaxation processes revealed by the action signals of intensity-modulated light fields. Phys. Rev. A 2016, 94, 053845. (40) Karki, K. J.; Kringle, L.; Marcus, A. H.; Pullerits, T. Phase-synchronous detection of coherent and incoherent nonlinear signals. J. Opt. 2015, 18, 015504. (41) Karki, K. J.; Abdellah, M.; Zhang, W.; Pullerits, T. Different emissive states in the bulk and at the surface of methylammonium lead bromide perovskite revealed by two-photon micro-spectroscopy and lifetime measurements. APL Photonics 2016, 1, 046103. (42) Fu, S.; Sakurai, A.; Liu, L.; Edman, F.; Pullerits, T.; Öwall, V.; Karki, K. J. Generalized lock-in amplifier for precision measurement of high frequency signals. Rev. Sci. Instrum. 2013, 84, 115101. (43) Karki, K.; Torbjörnsson, M.; Widom, J. R.; Marcus, A. H.; Pullerits, T. Digital cavities and their potential applications. J. Instrum. 2013, 8, T05005. (44) Sedgwick, P. Pearson’s correlation coefficient. Br. Med. J., 2012, 345, e4483.

TOC Graphic


Variation in the Photocurrent Response Due to Different Emissive

Recommend Documents