Upconversion-Assisted Dual-Band Luminescent Solar Concentrator

Article Cite This: ACS Photonics XXXX, XXX, XXX−XXX

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Upconversion-Assisted Dual-Band Luminescent Solar Concentrator Coupled for High Power Conversion Efficiency Photovoltaic Systems Su-Jin Ha,† Ji-Hwan Kang,‡ Dong Ho Choi,† Seong Kyung Nam,† Elsa Reichmanis,*,‡,§,∥ and Jun Hyuk Moon*,† †

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Department of Chemical and Biomolecular Engineering, Sogang University, 35 Baekbeom-ro, Mapo-gu, Seoul, 04107, Republic of Korea ‡ School of Chemical and Biomolecular Engineering, §School of Chemistry and Biochemistry, and ∥School of Materials Science and Engineering, Georgia Institute of Technology, 311 Ferst Drive NW, Atlanta, Georgia 30332, United States S Supporting Information *

ABSTRACT: A luminescent solar concentrator (LSC)-based photovoltaic (PV) system, consisting of an LSC panel that harvests light and an edge-mounted solar cell that produces electricity using the photoluminescent light, is promising for semitransparent building-integrated photovoltaics (BIPVs). Here, we demonstrate a highly efficient and highly semitransparent LSC-PVs capable of harvesting dual wavelength bands. We used a triplet−triplet annihilation-based photon upconversion (UC) LSC that luminesce high energy green light by absorbing low energy red light, as well as downshift LSC that luminesce green light by absorbing ultraviolet light. The luminescent light concentrated from the two LSCs is absorbed by a dye-sensitized solar cell (DSSC) having a high extinction coefficient at this wavelength. Our optimized dual band LSCPV exhibited 27% higher power conversion efficiency than the LSC-PV that absorb a single wavelength band. With respect to practical applications, the dual band LSC-DSSCs were fabricated in the form of an LSC window-DSSC window frame. We achieved a power conversion efficiency of 9.1% per LSC panel area. This dual-band LSC-DSSC exhibited high stability and maintained efficiency even at oblique illumination. Our results will be promising as an aesthetic and energy independent next generation BIPV. KEYWORDS: upconversion, luminescent solar concentrator, dye-sensitized solar cells, dual band, power conversion efficiency, organic dyes

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overlap of absorption and emission spectra of the dye molecules. To reduce such losses, optical components such as selective mirrors have been applied,8−11 and nanocrystals such as PbS/CdS, Mn:ZnSe, Cu:CdSe, and CuInSeS with fundamentally controlled fluorophore Stokes shifts have been studied.4,12−15 Nevertheless, the power conversion efficiency (PCE) of an LSC-PV system still has a moderate value. Previously, LSCs containing Culn S2/ZnS core/shell QDs integrated with Si solar cells reported a PCE of 1.2% under 1 sun solar illumination.16 An LSC comprising organic fluorophores with absorption of 420−480 nm wavelengths was combined with a crystalline Si solar cell that exhibited a PCE of 1.6%.17 The highest PCE of 5.3% was reported using GaAs solar cells and perylene and coumarin fluorophores containing LSC that absorbed 400−600 nm visible light.8 These PCEs are lower than the efficiency of commercial silicon solar cells (∼10%) or the efficiency of dye-sensitized solar cells (DSSCs, ∼12%),

uminescent solar concentrator-based photovoltaics (LSCPVs) is a system in which an LSC panel containing a luminescent material absorbs sunlight, and a PV system attached to the edge of the LSC panel generates electricity.1−3 An LSC differs from the conventional PV solar cell in that solar light is not directly incident on the PV system, rather the light concentrated by the LSC is guided to the PV system. LSCs are typically fabricated by doping glass or polymer panels with fluorophore organic molecules or by including fluorophore particles or quantum dots in the panel.1,4 An LSC is relatively transparent and aesthetic compared to solar cells made of electrode layers.10−13 Thus, LSC-PVs attract much attention as a semitransparent highly energy efficient building-integrated photovoltaics (BIPVs) applicable for use in windows or facades, which occupy high proportions of modern building exteriors.5,6 In an LSC-PV system, the area of the panel is much larger than the area of the edge, so concentrated light at the luminescence wavelength can enter the solar cell.5,7 In practice, the transport of light inside an LSC has optical loss from reflection on the panel surface, failure of total reflection because of scattering, and quantum yield loss because of the © XXXX American Chemical Society

Received: April 17, 2018

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DOI: 10.1021/acsphotonics.8b00498 ACS Photonics XXXX, XXX, XXX−XXX

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which are low-cost next-generation solar cells.18 Therefore, strategies from various perspectives to improve the PCE of LSC-PV are needed. In this study, we introduce a dual-band LSC-PV system capable of absorbing the ultraviolet (UV) wavelength band (300−450 nm) and red visible light (approximately 650 nm). These red and UV lights are converted to green light by downshifting and upconversion luminescence, respectively, resulting in harvesting by PV. The light harvesting of a wide range of wavelengths using multi-LSC panels has been reported previously, but most studies contained dyes that absorbed visible light; therefore, the average visible light transmittance was low.8 Our dual LSCs minimize the use of visible light, thereby exhibiting high visible light transmittance; the average visible light transmittance in the range of 400−700 nm was about 90%. Meanwhile, we utilized DSSCs for PVs. DSSCs exhibit lower a PCE because of their limited absorption band widths compared to those of other types of solar cells, but higher IPCE at certain wavelengths (e.g., green light).19,20 Considering that the light delivered by an LSC is a narrow wavelength band, the DSSC is more efficient and economical for this purpose. In the results, our dual-band LSC-DSSC achieved a PCE of up to 6.1%. The introduction of upconversion achieved an additional PCE improvement of 12%. We also developed a prototype LSC-DSSC in the form of a “window−window frame” that achieved a PCE (based on LSC panel area) of 9.1%.

and emitter molecules, and thus shows high quantum efficiency even under low-intensity illumination such as solar light.21 The PdTPBP/BPEA TTA UC mechanism is depicted in Figure 1a. Upon the light irradiation, the PdTPBP sensitizer populates the excited singlet state (S1*). In a transition-metal complex, such as PdTPBP, intersystem crossing (ISC) from the singlet (S1) to triplet excited state (T1) is favored due to spin−orbit coupling.22 When the sensitizer and emitter molecules are located within the so-called critical distance (typically within a few nanometres) through diffusion, triplet−triplet energy transfer (TTET) through a process known as Dexter energy transfer occurs.23 Subsequent diffusion and collision of the emitter molecules in the excited triplet state (T1) effect a triplet−triplet annihilation (TTA) process, resulting in a higher energy excited singlet state (S1*) of BPEA emitter.16,23,24 Here, the excited singlet state (S1*) of the emitter through the TTA has a higher energy state than the singlet state (S1*) of the sensitizer, resulting in the emission of the light of the upconverted wavelength.16,23,24 PdTPBP absorbs light in the wavelength range of 420−460 and 600−650 nm (see Figure S1). The photoluminescence (PL) emission spectrum for excitation of 600−650 nm wavelength light of the UC panel containing PdTPBP/BPEA is shown in Figure 1b. The results confirm that the absorption of the 630 nm wavelength results in the emission of the highest upconverted 510 nm wavelength light. Here, we optimized the concentration of PdTPBP, because it diffuses more slowly than BPEA due to its large molecular size. We fabricated LSCs containing PdTPBP concentrations ranging from 0.05 mM to 0.45 mM and measured PL spectra at 630 nm, as depicted in Figure 1c. These concentrations were calculated to have an average intermolecular distance within the approximately 10 nm critical distance. PL intensity increased with increasing concentration up to 0.11 mM PdTPBP, after which it decreased. An increase in PdTPBP concentration led to a decreased distance to emitter BPEA molecules, thus, TTET and subsequent TTA efficiency may be increased.25 However, the probability of reverse energy transfer from the emitter to the sensitizer may also increase, so that an optimum concentration may be observed.23 DS LSC panels were fabricated solely with BPEA. Upon UV absorption, BPEA is excited into a singlet state (S1*), converted to the lowest singlet state (S1) by rapid vibration relaxation, and then decayed to the ground state to emit lower energy visible light, as described in Figure 1d.26−28 BPEA exhibits broad absorption at wavelengths below 500 nm, as shown in Figure S1, due to various conformations of the two phenyl groups of BPEA.29,30 We observed the PL emission spectrum by adjusting the concentration of BPEA from 4.4 mM to 7.7 mM as shown in Figure 1f. The maximum emission was observed in a BPEA panel at a concentration of 5.5 mM and the intensity was up to five times higher than the 4.4 mM concentration. On the other hand, above this concentration, the emission decreases, due to fluorescence quenching associated with BPEA crystallization. The presence of BPEA microcrystals at high concentrations are shown in Figure S2.23 The dual panel LSC of UC and DS assembled with the DSSCs, as depicted in Figure 2a. Among various types of solar cells, DSSC has advantages of simple structure and high cost competitiveness.19,31,32 In particular, the sensitizer dye, D205, used in the DSSC, has a high extinction coefficient (7.6 × 104 cm−1, c.f., 1.0 × 104 cm−1 for Si solar cells) in the green wavelength band, which overlaps well with the wavelength of

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RESULTS AND DISCUSSION The dual-band LSC and its integration with a PV device and their light harvesting are depicted in Scheme 1. The dual-band Scheme 1. Concept of the Dual-Band LSC-PV Systema

a

Downshift LSC panel including emits visible light by absorbing ultraviolet light. Upconversion LSC panel emits green visible light by absorbing red light. These luminescent light is guided towards DSSCs.

LSC consists of a DS LSC, comprising a polyurethane panel containing an organic fluorophore that downshifts ultraviolet light, and an upconversion LSC panel containing an organic fluorophore pair capable of upconverting red light to green visible light. The converted luminescence light was concentrated within the LSC panel by total internal reflection and guided to the edge of the LSC, which was attached with a DSSC. The UC LSC utilized PdTPBP/BPEA as the sensitizer/ emitter fluorophore pair to induce triplet−triplet annihilation (TTA). Unlike traditional two-photon absorption processes, TTA UC utilizes the energy transferred between the sensitizer B

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Figure 1. (a) Energy diagram and UC process of BPEA/PdTPBP fluorophore pair system. (b) PL spectra of UC LSCs by excitation with 600−650 nm wavelength light. (c) Intensity of PL emission at 510 nm wavelength depending on the concentration of PdTPBP: values are normalized based on the maximum intensity. The concentration of BPEA was fixed at 5.5 mM. (d) Energy diagram and DS process of BPEA. (e) PL spectra of DS LSCs by excitation with 350−460 nm wavelength light. (f) Intensity of PL emission at 400 nm wavelength depending on the concentration of BPEA: values are normalized based on the maximum intensity.

Figure 2. (a) Photograph of light on a dual-band LSC. High intensity concentrated light emitted from the edge is observed. Schematic diagram showing that the emitted light is incident on the DSSC attached to the bottom edge. (b) Transmission spectrum of DS and UC LSC under 1 sun solar light irradiation. (c) Digital images of dual-band LSC. The panel has high transparency of visible light and clearly shows the rear building without haze. (d) Absorption spectra of D205 sensitizer dye used in DSSC and PL spectra of DS and UC LSC.

light that is concentrated in the LSC panel.33,34 The dimension of each LSC panel was 5 cm × 1 cm × 1 mm. DSSCs were bonded to the edge of the panel using an optical adhesive. Note that incident light first passes through DS, then enters

UC, as described in Figure 2a. This is to minimize the possibility that the BPEA contained in the UC panel absorbs the light of 450 nm wavelength and causes the DS process. Figure 2b shows the transmittance spectrum of the DS and UC C

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Figure 3. (a) J−V curves for the blank panel-DSSC, DS-DSSC, and DS/UC-DSSC. (b) The photocurrent of the DS and dual-band LSCs for various wavelength bands. The measurement was conducted by illuminating 1 sun solar light through a band-pass optical filter.

DSSC, respectively. We measured the JSC by increasing the thickness of the DS panel to three times that of the reference DS panel, and as a result, the JSC no longer increased above 1 mm thickness (see Figure S4). This indicates that the JSC of the DS-DSSC was the maximum photocurrent attainable by the single DS panel and that the additional JSC enhancement was achieved by the dual-band LSC. We compared our results with previous results using LSCs of similar area. Goldschmidt et al. achieved a PCE of 6.7% using two layers of LSC and InGaP solar cells containing a 2 cm × 2 cm organic dye.9 Currie et al. achieved a PCE of 6.8% using a two-layer 2.5 cm × 2.5 cm organic solar concentrator and a GaAs solar cell.3 The PCE of our dual-band LSC-DSSC are comparable to these results. Meanwhile, from the practical point of view, the PCE per cost is important. The cost per watt-peak of c-Si solar cells is about 2.34 $/Wp, and the same area of DSSCs is reported at 0.94 $/Wp, which is 40% of this price.35,36 InGaP or GaAs-based multijunction cells have a higher module cost than c-Si. Therefore, our LSC-DSSCs may show better cost-efficiency than these results. Figure 3b shows the photocurrent values at various wavelength bands. The selected wavelength band was obtained by passing 1 sun solar light through an optical band-pass filter. Both DS and UC/DS DSSCs measured a negligible photocurrent at 500−600 nm, as observed in Figure 3a, because these LSCs transmitted the light of a corresponding wavelength. The DS and DS/UC DSSCs showed a similar photocurrent in the 400−500 nm wavelength band, but only the DS/UC-DSSC showed a photocurrent at 600−700 nm owing to light harvesting in the UC LSC panel. The photocurrent value at 600−700 nm was about 13% of the photocurrent value at 400−500 nm; this value was similar to the JSC enhancement of the DS/UC-DSSC versus the DSDSSC. We verified the validity of the photocurrent values obtained by UC with a theoretical approach. In the LSC-PV system, the photocurrent value obtained from PV, JSC (mA/cm2) is described as

panels. The results show that the DS panel absorbs most of the light below 470 nm and has an average transmittance of 97% for the light above it. The UC panel absorbs the wavelengths of 600−650 nm, resulting in low transmittance at this wavelength range. As a result, the dual-band LSC transmits in the wavelength range of 470−600 nm, resulting in very high transparency in visible light (see Figure 2c); the average transmittance in the wavelength range of 400−700 nm was about 90%. High visible light transmittance enables this LSC to be applied as a window-type BIPV; however, the color of the LSC may be preferentially applied to the specialty window. Figure 2d shows the absorption band spectrum of the D205 dye and the emission spectrum of the DS and UC panels, confirming sufficient spectral matching. This indicates that the concentrated light in the dual band LSC is absorbed by the DSSC with high efficiency. The photovoltaic performance of a dual-band LSC coupled with DSSC was evaluated. The DSSCs used in this experiment exhibited a photocurrent density (JSC) of 16.7 mA/cm2 and a PCE of 7.4% (see Figure S3). The performances of the DS LSC and the blank panel without fluorophore were measured for comparison. The photocurrent density−voltage (J−V) plots of the DS-DSSC, DS/UC-DSSC, and blank-panel DSSC in Figure 3a and their photovoltaic parameters, including JSC, open-circuit voltage (VOC), and fill factor (FF), are listed in Table 1. The PCE was calculated by JSC × VOC × FF/100 mW Table 1. Photovoltaic Parameters Obtained from the J−V Curves of Figure 3 are Listed

blank DS-DSSC DS/UC-DSSC “window−window frame” DS/UC-DSSC

JSC (mA/cm2)

VOC (V)

FF

PCE (%)

0.6 13.2 15.0 20.6

0.71 0.71 0.70 0.64

0.58 0.58 0.58 0.69

0.3 5.4a 6.1a 9.1b

a The area of the LSC is 5 cm × 1 cm. The PCE were calculated by applying the DSSC active area (1 cm × 1 mm). bThis PCE were calculated by applying the LSC panel area (2 cm × 2 cm).

JSC =

cm−2. Here, JSC and PCE were calculated based on the photoelectrode area (approximately 1 cm × 1 mm) of the DSSCs. In the blank-panel LSC, a negligible JSC was observed, indicating that vertically incident light was not guided into the DSSC. The DS/UC-DSSC achieved a JSC of 15.0 mA/cm2 and a PCE of 6.1%, while the DS-DSSC showed a JSC of 13.2 mA/ cm2 and a PCE of 5.4%. The JSC and PCE of the DS/UCDSSC were 14% and 13% higher than each value of the DS-

λ ∫ 1240

× PLSC to PV(λ) ×

IPCE(λ) dλ 100

(1)

The DSSC (D205 sensitized) showed an average IPCE of approximately 78% in the wavelength range of 400−700 nm.19 PLSC to PV(λ) is the intensity of light incident on the solar cell concentrated in the LSC and is described as PLSC to PV(λ) = PLSC(λ) × ηabs × QY × G factor × ηwg (2) D

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Figure 4. (a) Digital image of “window−window frame” dual-band LSC-DSSCs. Four DSSCs are attached at the edge of LSC panel and the PV cells are wired in parallel. The size of the LSC panel for the LSC panel window is 2 cm × 2 cm. (b) J−V curves for DSSCs with electrode area of 2 cm × 2 cm and “window−window frame” LSC-DSSCs with the LSC panel area of 2 cm × 2 cm. (c) Normalized PCE dual band LSC-DSSCs measured for 400 h. (d) Normalized PCE of LSC-PV was measured at different incident angles in a range of 0−80°. The expected efficiency considering the cosine loss was also plotted.

essential to reduce this resistance.38,39 Thus, our dual band LSC-DSSC achieved similar efficiencies to the unit cells of the DSSC without losing the aesthetics by the metal grid. The long-term stability of the dual band LSC-DSSC was tested, as shown in Figure 4c. The photovoltaic parameters were observed over time while exposing the LSC-DSSC to a simulated solar light of 1 sun (AM 1.5G). Each parameter was normalized by its initial value. VOC and FF were maintained at almost 100%, according to the aging period, and JSC decreased by approximately 20% after 150 h. There was a reduction in efficiency (ηPV) of approximately 20%. This reduction in photovoltaic performance may be attributed to a decrease in electrolyte in the DSSC or due to photobleaching of dye molecules.8,40,41 Further, the performance of the LSC-PV system as a function of the angle of light illumination was measured, as presented in Figure 4d. The ηPV was evaluated by changing the incident angle and the angle of the LSC panel from 0° to 80°. The results are similar to the tendency of the cosine loss due to the increase in incident area with increasing angle.42,43 This indicates that stable photon-to-electric al energy conversion is allowed even in a practical environment where the light is not vertically incident on the panel.

From the left, each term corresponds to the intensity of light absorbed by the LSC, the absorption efficiency, the UC quantum yield, the G factor (ratio of plate area to edge area), and the waveguiding efficiency.1 We assumed that the UC LSC absorbed 100% of the light in the wavelength band of 600−650 nm. We obtained an UC QY of 4% (see the Supporting Information). Further, a maximum wave guiding efficiency of 75% at a refractive index of 1.5 of the LSC panel was applied. The G factor was 50. The JSC calculated by these assumptions and values was about 3 mA/cm2. In our results, the UC LSC achieved a photocurrent density of about 1.8 mA/cm2; therefore, this value is not an overestimated value. Meanwhile, the theoretical photocurrent density calculation for DS is shown in the Supporting Information. The practical implementation of the LSC-PV system is in the form of a “window−window frame”.37 We fabricated a dual band LSC window with all of the edges surrounded by DSSC window frame, as shown in Figure 4a. In this experiment, an LSC with an area of 2 cm × 2 cm was applied and integrated with four DSSCs connected in parallel. Here, for comparison, DSSCs with photoelectrodes having the same area (2 cm × 2 cm) were fabricated and the J−V curve was recorded by directly irradiating the electrode with light. The J−V curves of DSSC and LSC-DSSC are shown in Figure 3b. The PCE of dual-band LSC-DSSCs was 9.1%, while the PCE achieved by the DSSC was 2.8%. The LSC-DSSC exhibited much higher efficiency compared to stand-alone DSSCs. The low PCE of DSSCs is due to low JSC and FF. This is due to the large resistance of the electrode itself at the large area electrode. For large area solar cells, additional metal grid electrodes are

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CONCLUSION Conventional LSC studies have limited the conversion efficiency per LSC area by converting only a single wavelength band corresponding to a part of the sunlight spectrum. Here, we introduced a dual-band LSC that harvests both ultraviolet and red visible light by using two types of LSCs of UC and DS. The dual-band LSC-DSSCs exhibited 27% higher PCE than E

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the LSC that only harvest a single wavelength band. With respect to practical applications, LSC-PVs in the form of a “window−window frame” were fabricated. Their PCE was 9.1%. In addition, our dual-band LSC-DSSC exhibited high stability and maintained efficiency even at oblique illumination. Our results will be promising as an aesthetic and energy independent next generation BIPV.

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. ORCID

Jun Hyuk Moon: 0000-0002-4776-3115

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Author Contributions

METHODS Preparation of LSC Panel and DSSCs. We dissolved 1 mg of meso-tetraphenyl-tetrabenzoporphine palladium complex (PdTPBP, Chemodex) and 2.5 mg of 9,10-bispenylethynylanthrancence (BPEA, Sigma-Aldrich) in 1 mL of chloroform, respectively. For upconversion LSC, we mixed PdTPBP and BPEA solution with polyurethane (Clear Flex 50) and evaporated chloroform by using rotary evaporator. The consequent viscous polyurethane (PU) solution was sandwiched between glass substrates, followed by cross-linking at room temperature for 12 h. These glass substrates were removed after the cross-linking. The thickness of the LSC panel was approximately 1 mm. For downshift LSC, we only mixed the BPEA solution with polyurethane and the subsequent process is the same as the process of preparing the UC. Dye-sensitized solar cells (DSSCs) consist of TiO2 photoanode, Pt-coated FTO, and electrolyte. For the photoelectrode, TiO2 nanoparticle paste (DSL 18NR-T, Dyesol) was doctor-bladed on FTO, followed by heating at 500 °C for 15 min. The TiO2 film was sensitized by immersion in a dye solution (D205, Mitsubishi paper mills limited, 0.5 mM) for over 12 h. The counter electrode was prepared by coating a 0.5 mM H2PtCl6 solution, followed by heat treatment at 450 °C for 30 min. The TiO2 photoanode and Pt counter electrode were sandwiched with a 60 μm gap using a spacer film (Surlyn, DuPont). Finally, the electrolyte solution, which was prepared by dissolving 25 mM Lil (Aldrich), 55 mM I2 (Yakuri), 0.6 M dimethyl-propyl imidazole iodide (DMPII, TCI), 0.1 M guanidinium thiocyanate (GuSCN, Aldrich), 22 mM Co(bpy) 3 (PF 6 ) 2 (Dyenamo), and 5 mM Co(bpy) 3 (PF6) 3 (Dyenamo) in an 8.5:1.5 (v/v) ratio with a mixture of acetonitrile (Aldrich) and valeronitrile (Aldrich), was injected into the cell. Characterization. The absorption and photoluminescence were measured by using UV−vis spectrometry (SHIMADZU, UV-2550) and spectrofluorophotometry (SHIMADZU, RF6000), respectively. The J−V characteristics of the DSSCs were measured using a source meter (Keithley Instruments) under 1 sun illumination. The solar light was produced by a 150 W Xe lamp (300 W, Oriel) and AM 1.5 G filters. The intensity of the solar light was adjusted by using a Si reference cell (BS-520, Bunko-Keiki) to simulate a power density of 100 mW/cm2.

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S.J.H., J.H.K., and J.H.M. designed this work, and S.J.H. performed the experiments. E.R. supervised the experiments and edited the manuscript. J.H.M. supervised the whole process and wrote the manuscript. D.H.C. and S.K.N. conducted experiments for revision. Funding

This work was supported by grants from the National Research Foundation of Korea (2011−0030253, 2016M3D3A1A01913254). The Korea Basic Science Institute is also acknowledged for the SEM measurement. Notes

The authors declare no competing financial interest.

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REFERENCES

(1) Debije, M. G.; Verbunt, P. P. C. Thirty Years of Luminescent Solar Concentrator Research: Solar Energy for the Built Environment. Adv. Energy Mater. 2012, 2 (1), 12−35. (2) Meinardi, F.; Colombo, A.; Velizhanin, K. A.; Simonutti, R.; Lorenzon, M.; Beverina, L.; Viswanatha, R.; Klimov, V. I.; Brovelli, S. Large-Area Luminescent Solar Concentrators Based on “StockesShift-Engineered” Nanocrystals in a Mass-Polymerized Pmma Matrix. Nat. Photonics 2014, 8, 392−399. (3) Currie, M. J.; Mapel, J. K.; Heidel, T. D.; Goffri, S.; Baldo, M. A. High-Efficiency Organic Solar Concentrators for Photovoltaics. Science 2008, 321, 226−228. (4) Meinardi, F.; Bruni, F.; Brovelli, S. Luminescent Solar Concentrators for Building-Integrated Photovoltaics. Nat. Rev. Mater. 2017, 2 (12), 17072. (5) Debije, M. Better Luminescent Solar Panels in Prospect. Nature 2015, 519, 298−299. (6) Vasiliev, M.; Alghamedi, R.; Nur, E. A. M.; Alameh, K. Photonic Microstructures for Energy-Generating Clear Glass and Net-Zero Energy Buildings. Sci. Rep. 2016, 6, 31831. (7) Zhou, J.; Liu, Q.; Feng, W.; Sun, Y.; Li, F. Upconversion Luminescent Materials: Advances and Applications. Chem. Rev. 2015, 115 (1), 395−465. (8) Sark, W. G. J. H. M. v.; Barnham, K. W. J.; Slooff, L. H.; Chatten, A. J.; Büchtemann, A.; Meyer, A.; McCormack, S. J.; Koole, R.; Farrell, D. J.; Bose, R.; Bende, E. E.; Burgers, A. R.; Budel, T.; Quilitz, J.; Kennedy, M.; Meyer, T.; Donegá, C. D. M.; Meijerink, A.; Vanmaekelbergh, D. Luminescent Solar Concentrators - a Review of Recent Results. Opt. Express 2008, 16 (26), 21773−21792. (9) Goldschmidt, J. C.; Peters, M.; Boesch, A.; Helmers, H.; Dimroth, F.; Glunz, S. W.; Willeke, G. Increasing the Efficiency of Fluorescent Concentrator Systems. Sol. Energy Mater. Sol. Cells 2009, 93 (2), 176−182. (10) Debije, M. G.; Van, M.-P.; Verbunt, P. P. C.; Kastelijn, M. J.; van der Blom, R. H. L.; Broer, D. J.; Bastiaansen, C. W. M. Effect on the Output of a Luminescent Solar Concentrator on Application of Organic Wavelength-Selective Mirrors. Appl. Opt. 2010, 49 (4), 745− 751. (11) de Boer, D. K. G.; Lin, C.-W.; Giesbers, M. P.; Cornelissen, H. J.; Debije, M. G.; Verbunt, P. P. C.; Broer, D. J. PolarizationIndependent Filters for Luminescent Solar Concentrators. Appl. Phys. Lett. 2011, 98 (2), 021111. (12) Meinardi, F.; McDaniel, H.; Carulli, F.; Colombo, A.; Velizhanin, K. A.; Makarov, N. S.; Simonutti, R.; Klimov, V. I.; Brovelli, S. Highly Efficient Large-Area Colourless Luminescent Solar

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsphotonics.8b00498. Absorption spectra of PdTPBP and BPEA; Microscope image of DS panel; J−V curve for DSSC; Photocurrent densities for DS panels with various thicknesses; Note for the calculation of quantum yield (PDF). F

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DOI: 10.1021/acsphotonics.8b00498 ACS Photonics XXXX, XXX, XXX−XXX