Research Article Cite This: ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX
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Colorful Squaraines Dyes for Efficient Solution-Processed All SmallMolecule Semitransparent Organic Solar Cells Daobin Yang,† Takeshi Sano,*,† Hisahiro Sasabe,*,† Lin Yang,‡ Satoru Ohisa,† Yao Chen,‡ Yan Huang,*,‡ and Junji Kido*,† †
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Research Center for Organic Electronics (ROEL), Frontier Center for Organic Materials (FROM), Department of Organic Materials Science, Yamagata University, Yonezawa 992-8510, Japan ‡ College of Chemistry, Key Laboratory of Green Chemistry and Technology of Ministry of Education, Sichuan University, Chengdu 610064, China S Supporting Information *
ABSTRACT: Semitransparent organic solar cells (ST-OSCs) exhibit highly promising applications to develop integrated photovoltaics and power-generating windows. However, the development of ST-OSCs is significantly lagging behind opaque OSCs, especially for all small-molecule ST-OSCs. Here, four unique squaraines dyes (IDPSQ, SQ-BP, D-BDT-SQ, and AzUSQ) were successfully used as donors in ST-OSCs, whose colors can be tuned from purple to blue, green, and dark green, respectively. While using ultrathin Ag as a transparent electrode, the ST-OSCs fabricated using IDPSQ:PC71BM, SQ-BP:PC71BM, D-BDTSQ:PC71BM, and AzUSQ:PC71BM yield power conversion efficiencies (PCEs) of 2.96, 4.36, 4.91, and 1.71%, respectively, and their colors are purple, cyan, brown, and light brown, respectively. Compared to their opaque OSCs (PCEs of 3.95, 5.45, 5.84, and 1.91%, respectively), the reduction in the PCEs are as low as 25, 20, 16, and 10%, respectively. Furthermore, each of these ST-OSCs exhibit good average visible transmittance (AVT) of 25− 30%, favorable CIE color coordinates, and a color rendering index (CRI) of 71−97%. Finally, by changing the thickness of the Ag electrode, an impressive PCE of 4.9% along with an AVT of 25% and a CRI of 97% can be obtained in D-BDT-SQ:PC71BM-based ST-OSCs, which is the highest PCE among all smallmolecule ST-OSCs. KEYWORDS: squaraines dyes, colorful, solution-processed, small molecules, semitransparent organic solar cells metal films, nanowire, graphene, and conducting polymers.9−14 Not much attention was focused on the materials of the active layer.6,7 Furthermore, the active layer materials can be mainly divided into two classes, i.e., polymers and small molecules. Very recently, some highly efficient semitransparent polymer solar cells having PCE of 7−10% have been reported.15−18 Nevertheless, many studies have depicted that the intrinsic batch-tobatch variation issue of polymers originating from different polymerization degrees and polydispersity indexes can impact the reproducibility of the device performance.19−21 In comparison to the polymeric counterparts, small-molecule OSCs should be more promising owing to their well-defined molecular structures, accurate molecular weights, and high purity without batch-to-batch variations.1,3 Furthermore, the color of the small molecule is easily modifiable because of their facile molecular modulations. However, only two studies that have been conducted on solution-processed all small-molecule ST-OSCs to date, and the best PCE of these devices was observed to be only 3.6%, while having CIE color coordinates of
1. INTRODUCTION Organic solar cells (OSCs) are considered to be a promising next-generation green energy technology due to several advantages, such as being economical, flexible, lightweight, and capable of large-scale production.1−3 Due to the large number of studies conducted on photovoltaic materials as well as optimizing the morphology, the highest power conversion efficiency (PCE) of traditional opaque OSCs exceeded 15%.4 However, OSCs should exhibit high performance and long-term stability as well as unique features for broader applications, such as semitransparent solar cells and transparent solar cells, to further realize commercialization. Recently, developing semitransparent organic solar cells (ST-OSCs) has been considered to become one of the highest priorities in the market of nextgeneration solar cells because ST-OSCs enable wearable electronics, solar-powered automotive, power-generating windows, and building integrated photovoltaics as electricitygenerating facades, shelters, roofs, and windows.5−7 Furthermore, ST-OSCs can be easily fabricated by reducing the thickness of the active layers and using transparent top electrodes.8 To date, most efforts in ST-OSCs have been devoted to develop high-transparency top electrodes, such as ultrathin © XXXX American Chemical Society
Received: May 29, 2018 Accepted: July 12, 2018
A
DOI: 10.1021/acsami.8b08878 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX
Research Article
ACS Applied Materials & Interfaces
Figure 1. Chemical structures of the four squaraines.
whose absorption spectra are located in the visible or nearinfrared regions showing absorption peaks at 574, 692, 747, and 814 nm, respectively (Figure 2).34−36 Further, the correspond-
(0.386, 0.357), which was much lower than its opaque device with a PCE of 8.2%.22,23 The blend film of this device exhibited absorption in the visible region, but almost no absorption in the near-infrared region with a moderate absorption coefficient of less than 105 M−1 cm−1, which is mainly responsible for the significantly reduced PCE. Unlike opaque OSCs, there are some critical requirements that should be met by ST-OSCs, in addition to the PCE. They are as follows: (1) the average visible transmittance (AVT, 370−740 nm) of the devices should be enough for the applications in windows (typically over 25%); (2) the CIE color coordinates of the devices should be in close proximity to the white color point (0.333, 0.333), since this condition is generally preferred for window applications; (3) the devices should have good color rendering index (CRI) and should be colorful to satisfy the requirements of various applications.6,24,25 Therefore, it is a great challenge for all small-molecule ST-OSCs to achieve high PCE along with high AVT, favorable CIE, and high CRI. In the past decade, squaraines dyes have gradually drawn attention for opaque organic photovoltaic applications, such as ternary solar cells, quaternary solar cells and tandem solar cells,26−31 and light-responsive transistors.32 The most important reason is that squaraines dyes possess intense and broad absorption in visible and near-infrared spectral regions with extremely high optical density (typically over 105 cm−1) or absorption coefficient (typically over 105 M−1 cm−1), which leads to high short-circuit current density (Jsc). Another reason is their facile, low-cost synthesis as well as an easily changed absorption. However, there has only been a single example for squaraine-based ST-OSC to date, which exhibited a PCE as low as 0.5%.22 This low PCE is attributed to the relatively high highest occupied molecular orbital (HOMO) energy level of −5.0 eV and low hole mobility of 2.7 × 10−5 cm2 V−1 s−1.33 Therefore, we assume that ST-OSCs having much higher efficiencies can be developed using powerful squaraines dyes with low HOMO energy levels and high hole mobilities. In this study, four colorful and efficient squaraines dyes (IDPSQ, SQ-BP, D-BDT-SQ, and AzUSQ) are used as donors in ST-OSCs (Figure 1) on the basis of our previous reports,
Figure 2. Normalized absorption spectra and photographs of the four pure squaraine films: (a) IDPSQ, (b) SQ-BP, (c) D-BDT-SQ, and (d) AzUSQ.
ing colors can be tuned from purple to blue, green, and dark green, which is very suitable to fabricate colorful windows. Additionally, the thickness of the active layer of the squarainebased OSCs is very low (usually less than 80 nm), which is quite remarkable and enhances AVT even further. While using a 10 nm Ag as a transparent electrode, the ST-OSCs fabricated using IDPSQ:PC71BM, SQ-BP:PC71BM, D-BDT-SQ:PC71BM, and AzUSQ:PC71BM exhibit PCEs of 2.96, 4.36, 4.57, and 1.63%, with AVTs of 29.2, 25.7, 30.0, and 30.9%, respectively, whose colors are purple, green, brown, and light brown, respectively. Furthermore, the photovoltaic performance of ST-OSCs is completely investigated, and the D-BDT-SQ:PC71BM-based ST-OSCs exhibit an impressive PCE of 4.91% with an AVT of 25.1%, a CIE color coordinate of (0.328, 0.327), and a CRI of B
DOI: 10.1021/acsami.8b08878 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX
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ACS Applied Materials & Interfaces
Figure 3. J−V characteristics of the semitransparent devices and opaque devices based on (a) IPQSQ:PC71BM (1:3), (b) SQ-BP:PC71BM (1:3), (c) D-BDT-SQ:PC71BM (1:6), and (d) AzUSQ:PC71BM (1:2). Programmable Surface Profiler Measuring System. Further, these substrates were heated to 80 °C for 10 min. Subsequently, the substrates were transferred into a high-vacuum chamber, and the bathocupuroine (BCP) (3 nm) was deposited as the hole-blocking layer (HBL) at a pressure less than 6 × 10−5 Pa at a rate of 0.20 Å s−1. Finally, the Ag electrode (10, 12, 14, and 20 nm for semitransparent devices and 100 nm for opaque devices) was deposited onto the HBL using a shadow mask subjected to a pressure less than 8 × 10−5 Pa at a rate of 0.20 Å s−1. The active area of organic solar cells is 9.0 mm2. Additionally, current density−voltage (J−V) and external quantum efficiency (EQE) characterizations of organic solar cells are performed on a CEP-2000 integrated system manufactured by Bunkoukeiki Co. The integration of EQE data over an AM 1.5 G solar spectrum that was yielded is used to estimate Jsc values using an experimental variation of less than 5% relative to the Jsc measured under 100 mW cm−2 simulated AM 1.5 G light illumination. All of the measurements were carried out in ambient air.
97%. This is, to the best of our knowledge, the highest PCE for all small-molecule ST-OSCs.
2. EXPERIMENTAL SECTION 2.1. Materials and Optical Characterization. PC71BM was purchased from Solarmer Energy, Inc., and the three squaraines dyes SQ-BP, D-BDT-SQ, and AzUSQ were synthesized according to the procedures described in the literature.34−36 The synthetic route of IDPSQ is shown in Supporting Information. Absorption spectra of the thin-film samples of squaraines dyes and transmittance spectra of semitransparent devices were recorded using a SHIMADZU UV-3150 UV−vis−NIR spectrophotometer. The thin-film samples of squaraines dyes were obtained from a chloroform solution (8 mg mL−1, 1500 rpm/ 40 s) by spin-coating on quartz substrates. 2.2. Fabrication and Characterization of Devices. Organic solar cells were fabricated using indium tin oxide (ITO)-coated glass as the substrate having a sheet resistance of 10 Ω sq−1. Patterned ITOcoated glass substrates were sequentially cleaned using detergent, deionized water, acetone, and isopropanol in an ultrasonic bath for 30 min each, and the cleaned substrates were dried in an oven at 65 °C for 12 h before use. The substrates were treated by UV-ozone for 20 min. Further, the substrates were immediately transferred into a highvacuum chamber for the deposition of an 8 nm layer of MoO3 at a pressure of less than 2 × 10−4 Pa with a rate of 0.20 Å s−1. Subsequently, photoactive layers were fabricated by spin-coating a blend of IDPSQ and PC71BM (1:3, wt %, 60 nm), SQ-BP and PC71BM (1:3, wt %, 60 nm), D-BDT-SQ and PC71BM (1:6, wt %, 70 nm), and AzUSQ and PC71BM (1:2, wt %, 60 nm) in chloroform with total concentration of 20 mg mL−1 in a N2-filling glovebox at 40 °C for 2 h. The thickness of the photoactive layers is 65 ± 5 nm, which is measured by
3. RESULTS AND DISCUSSION 3.1. Photovoltaic Performances. To demonstrate the potential application of these squaraines dyes in ST-OSCs, bulk heterojunction (BHJ) devices having a conventional structure of indium tin oxide (ITO)/MoO3/squaraine:PC71BM/BCP/Ag were fabricated using ultrathin Ag as the top electrode because the Ag electrode possesses a high work function along with air stability, high conductivity, and intrinsically long skin depth, which facilitates penetration of photons.8,37 According to our previous reports, 34−36 the optimized blend ratios of IDPSQ:PC71BM, SQ-BP:PC71BM, D-BDT-SQ:PC71BM, and C
DOI: 10.1021/acsami.8b08878 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX
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Figure 4. Transmittance spectra of ST-OSCs with various thicknesses of Ag acting as transparent cathodes.
Table 1. Photovoltaic Performances and AVTs of the ST-OSCs Based on Squaraines:PC71BM Blend Films and Various Thicknesses of the Ag-Film Electrode squaraines IDPSQ
SQ-BP
D-BDT-SQ
AzUSQ
Ag (nm)
Voca (V)
Jsca (mA cm−2)
FFa
PCEa (%)
AVT (%)
10 12 14 20 100 10 12 14 20 100 10 12 14 20 100 10 12 14 20 100
1.00 (1.00 ± 0.01) 1.00 (1.00 ± 0.01) 1.00 (1.00 ± 0.01) 1.01 (1.01 ± 0.01) 1.02 (1.01 ± 0.01) 0.97 (0.97± 0.01) 0.97 (0.98 ± 0.01) 0.97 (0.97 ± 0.01) 0.97 (0.97 ± 0.01) 0.98 (0.98 ± 0.01) 0.88 (0.88 ± 0.01) 0.88 (0.88 ± 0.01) 0.88 (0.88 ± 0.01) 0.88 (0.88 ± 0.01) 0.89 (0.89 ± 0.01) 0.77 (0.76 ± 0.01) 0.77 (0.77 ± 0.01) 0.77 (0.77 ± 0.01) 0.77 (0.77 ± 0.01) 0.77 (0.77 ± 0.01)
7.80 (7.67 ± 0.22) 8.24 (8.11 ± 0.13) 8.44 (8.35 ± 0.19) 9.38 (9.33 ± 0.41) 9.93 (9.77 ± 0.20) 10.21 (10.05 ± 0.16) 10.56 (10.58 ± 0.11) 10.72 (10.61 ± 0.28) 11.47 (11.27 ± 0.30) 12.63 (12.53 ± 0.15) 10.82 (10.68 ± 0.14) 11.38 (11.15 ± 0.23) 11.76 (11.60 ± 0.16) 11.90 (11.79 ± 0.15) 13.38 (13.21 ± 0.19) 5.71 (5.65 ± 0.12) 5.86 (5.64 ± 0.22) 6.03 (5.84 ± 0.20) 6.35 (6.07 ± 0.28) 6.70 (6.56 ± 0.14)
0.38 (0.38 ± 0.01) 0.37 (0.37 ± 0.01) 0.37 (0.37 ± 0.01) 0.39 (0.38 ± 0.01) 0.39 (0.39 ± 0.01) 0.44 (0.43± 0.01) 0.44 (0.43 ± 0.01) 0.44 (0.44 ± 0.01) 0.45 (0.45 ± 0.01) 0.44 (0.44 ± 0.01) 0.48 (0.48 ± 0.01) 0.49 (0.49 ± 0.01) 0.48 (0.48 ± 0.01) 0.48 (0.48 ± 0.01) 0.49 (0.49 ± 0.01) 0.37 (0.37 ± 0.01) 0.38 (0.38± 0.01) 0.38 (0.38 ± 0.01) 0.37 (0.37 ± 0.01) 0.37 (0.37 ± 0.01)
2.96 (2.90 ± 0.06) 3.05 (3.00 ± 0.05) 3.12 (3.09 ± 0.03) 3.69 (3.58 ± 0.11) 3.95 (3.85 ± 0.10) 4.36 (4.21 ± 0.15) 4.51 (4.46 ± 0.05) 4.58 (4.53 ± 0.05) 5.01 (4.92 ± 0.09) 5.45 (5.40 ± 0.05) 4.57 (4.51 ± 0.06) 4.91 (4.81 ± 0.10) 4.97 (4.90 ± 0.07) 5.03 (4.98 ± 0.05) 5.84 (5.76 ± 0.08) 1.63 (1.59 ± 0.04) 1.71 (1.65 ± 0.05) 1.76 (1.71 ± 0.05) 1.81 (1.73 ± 0.08) 1.91 (1.87 ± 0.04)
29.2 24.3 20.5 10.0 25.7 21.4 18.1 9.3 30.0 25.1 20.7 11.2 30.9 26.6 22.3 12.1
a
Average values of eight individual cells together with standard deviations are given in parentheses.
AzUSQ:PC71BM are 1:3, 1:3, 1:6, and 1:2, respectively. The J−
and 4, respectively. The corresponding parameters of the various
V curves and transmittance spectra are illustrated in Figures 3
devices are summarized in Table 1. D
DOI: 10.1021/acsami.8b08878 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX
Research Article
ACS Applied Materials & Interfaces By gradually reducing the thickness of the Ag electrode from 20 to 10 nm, the AVTs of the ST-OSCs fabricated using IDPSQ:PC71BM, SQ-BP:PC71BM, D-BDT-SQ:PC71BM, and AzUSQ:PC71BM exhibited an increase from 10.0 to 29.2%, 9.3 to 25.7%, 11.2 to 30.0%, and 12.1 to 30.9%, respectively, which indicates that these AVTs mainly depend on the thickness of the Ag electrode. However, the PCEs of their corresponding STOSCs slightly decrease from 3.69 to 2.96%, 5.01 to 4.36%, 5.03 to 4.57%, and 1.81 to 1.63%, which should be mainly attributed to their relatively low Jsc stemming from the reduced reflectivity of the thin anode electrode reduced light intensity in the active layer. Additionally, no distinct changes can be observed for the Voc and fill factor (FF) of these devices when the thickness of the Ag electrode reduces from 20 to 10 nm. While squaraines-based BHJ-OSCs can deliver high Voc and Jsc, they usually suffer from a low FF stemming from the relatively low hole mobility and high bimolecular recombination rate.29,38 Regrettably, there has been no effective way to overcome this problem to date. While using the 100 nm Ag electrode, the traditional opaque devices fabricated using IDPSQ:PC71BM, SQ-BP:PC71BM, DBDT-SQ:PC71BM, and AzUSQ:PC71BM exhibit PCEs of 3.95, 5.45, 5.84, and 1.91%, respectively, with Voc values of 1.02, 0.98, 0.88, and 0.77 V, respectively. By using ultrathin Ag (10 or 12 nm) as electrodes, the corresponding ST-OSCs yield PCEs of 2.96, 4.36, 4.91, and 1.71%, respectively, with AVTs of 29.2, 25.7, 25.1, and 26.6%, respectively. To the best of our knowledge, the PCE of 4.91% with an AVT of 25.1% is the highest value for all small-molecule ST-OSCs to date. In comparison to the opaque devices, the decreases in the PCEs of IDPSQ:PC71BM-, SQ-BP:PC71BM-, D-BDT-SQ:PC71BM-, and AzUSQ:PC71BM-based ST-OSCs are as low as 25, 20, 16, and 10%, respectively, which should be attributed to squaraines’s intense absorption in visible and near-infrared spectral regions. This decrease in PCEs is rarely observed for ST-OSCs. Furthermore, the decrease in the PCEs of the ST-OSCs gradually reduces with the red shift in the absorption of squaraines. As a result, squaraines dyes are very promising to be applied to ST-OSCs. 3.2. Color of Blend Films. The color of ST-OSCs is highly dependent on the blend film, whose color is determined by the absorption properties of both the donor and acceptor. The absorption spectra and photographs of the blend films manufactured using IDPSQ:PC71BM, SQ-BP:PC71BM, DBDT-SQ:PC71BM, and AzUSQ:PC71BM are depicted in Figure 5. Since a and b have very strong absorption in the visible range, the colors of their blend films are highly dependent on the donor (IDPSQ and SQ-BP). Whereas, the color of the blend film relies on the acceptor due to the low weight ratio (14%) of D-BDT-SQ in the blend film. For AzUSQ:PC71BM system, the color is also dependent on the acceptor for AzUSQ:PC71BM system because AzUSQ possesses strong absorption in the near-infrared region. Therefore, the colors of the IDPSQ:PC71BM-, SQ-BP:PC71BM-, D-BDT-SQ:PC71BM-, and AzUSQ:PC71BM-blend films are purple, cyan, brown, and light brown, respectively, which can be used to create colorful windows. 3.3. EQE Curves. The external quantum efficiency (EQE) curves of the ST-OSCs fabricated using a 10 nm Ag electrode and the opaque OSCs are displayed in Figure 6, in which the curves are consistent with the absorption spectra of the corresponding active layers. The integrated current densities of the EQE spectra of the IDPSQ:PC71BM, SQ-BP:PC71BM, DBDT-SQ:PC71BM, and AzUSQ:PC71BM-based opaque devices are 9.6, 12.1, 12.9, and 6.4 mA cm−2, respectively, which are in
Figure 5. Absorption spectra and the photographs of the four blend films based on (a) IDPSQ:PC71BM (1:3), (b) SQ-BP:PC71BM (1:3), (c) D-BDT-SQ:PC71BM (1:6), and (d) AzUSQ:PC71BM (1:2).
agreement with the Jsc values obtained from the J−V measurements. In comparison to the opaque devices, the EQE values of the ST-OSCs decrease throughout the spectral response regions, which results in lowered Jsc. The corresponding integrated current densities reduce to 7.5, 9.8, 10.4, and 5.6 mA cm−2. 3.4. Transparency Color Perception. In addition to PCE and AVT, the transparency color perception of ST-OSCs is a critical factor to evaluate the overall color property of the devices.6,39 To analyze the transparency color perception for the human eye, the CIE 1931 color coordinate is calculated from the transmitted light and is represented by the product of standard daylight (D65) illuminant spectrum and the transmittance spectrum of each ST-OSCs device. The CIE 1931 and CIE 1960 color coordinates of the representative ST-OSCs are summarized in Table 2 and are depicted in the CIE 1931 XY chromaticity diagram in Figure 7. The corresponding color coordinates of ST-OSCs are (0.288, 0.265) for the IDPSQ:PC71BM system, (0.280, 0.322) for the SQ-BP:PC71BM system, (0.328, 0.327) for the D-BDT-SQ:PC71BM system, and (0.302, 0.330) for the AzUSQ:PC71BM system. Except for the IDPSQ:PC71BM system, the color coordinates of the other three systems are very close to the white point (0.333, 0.333), which indicates that they have a very high-transparency color perception. 3.5. Color Rendering Index Property. Further, the color rendering index property of ST-OSCs is an important characteristic when they are integrated in windows, shelters, and roofs, which further describes the capability of the transmitted light by the ST-OSCs for producing the true colors of the viewed objects.6,24 The CRI of the transmitted light has been calculated under the illumination of daylight (D75) for IDPSQ:PC71BM, SQ-BP:PC71BM, and AzUSQ:PC71BM systems, while the CRI of the transmitted light was calculated under the illumination of daylight (D55) for D-BDT-SQ:PC71BM system.6,24 Generally, a higher CRI means better color rendering capacity, which leads to higher neutral color degree. As shown in Table 2, the IDPSQ:PC71BM- and SQ-BP:PC71BM-based STOSCs exhibit moderate CRI values of 71 and 80, respectively. However, the CRI values of D-BDT-SQ:PC 71BM- and AzUSQ:PC71BM-based ST-OSCs are observed to be as high as 97 and 92, respectively, because of their strong near-infrared absorption, which means that they have a very high neutral color E
DOI: 10.1021/acsami.8b08878 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX
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ACS Applied Materials & Interfaces
Figure 6. EQE curves of the semitransparent devices and opaque devices based on (a) IDPSQ:PC71BM (1:3), (b) SQ-BP:PC71BM (1:3), (c) D-BDTSQ:PC71BM (1:6), and (d) AzUSQ:PC71BM (1:2).
Table 2. Optical Properties of the Representative ST-OSCs based on Squaraines:PC71BM squaraines
Ag (nm)
AVT (%)
PCE (%)
CIE 1931 (x, y)
CIE 1960 (u, v)
DC
CRI
IDPSQ SQ-BP D-BDT-SQ AzUSQ
10 10 12 12
29.2 25.7 25.1 26.6
2.96 4.36 4.91 1.71
(0.288, 0.265) (0.280, 0.322) (0.328, 0.327) (0.302, 0.330)
(0.206, 0.284) (0.178, 0.306) (0.209, 0.313) (0.190, 0.312)
0.0178 0.0173 0.0057 0.0093
71 80 97 92
4. CONCLUSIONS In summary, we have successfully developed efficient solutionprocessed all small-molecule ST-OSCs by incorporating four colorful squaraines. By using a 10 nm Ag as the transparent electrode, the ST-OSCs fabricated using IDPSQ:PC71BM, SQBP:PC71BM, D-BDT-SQ:PC71BM, and AzUSQ:PC71BM exhibit PCEs of 2.96, 4.36, 4.57, and 1.63% with AVTs of 29.2, 25.7, 30.0, and 30.9%, respectively, whose colors are purple, cyan, brown, and light brown, respectively. In comparison to their opaque OSCs, any decrease in the PCEs of ST-OSCs is observed to be less than 25%, which is very rare for ST-OSCs. Furthermore, the SQ-BP:PC71BM-, D-BDT-SQ:PC71BM-, and AzUSQ:PC71BM-based ST-OSCs exhibit very high transparent color perception and color rendering properties. Finally, the relationships between the PCEs and AVTs are investigated in detail by modifying the thickness of the Ag electrode, and an impressive PCE of 4.91% with an AVT of 25.1% and a CRI of 97% can be achieved using the D-BDT-SQ:PC71BM-based STOSCs, which is the highest PCE for all small-molecule STOSCs. This remarkable result indicates that squaraines dyes should be considered as very promising candidates to promote the development of colorful ST-OSCs. Further, these colorful squaraines dyes create scope for the development of tandem solar cells and solar sharing for agriculture.
Figure 7. CIE 1931 XY chromaticity diagram depicting the color coordinates of the representative ST-OSCs based on (a) IDPSQ:PC71BM (1:3), (b) SQ-BP:PC71BM (1:3), (c) D-BDTSQ:PC71BM (1:6), and (d) AzUSQ:PC71BM (1:2).
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ASSOCIATED CONTENT
S Supporting Information *
degree. Besides, the chromaticity differences (DC) of ST-OSCs are shown in Table 2. DC is the shortest distance between the color coordinates on the CIE 1960 uniform color space and the black body locus. For IDPSQ:PC71BM-, SQ-BP:PC71BM-, and AzUSQ:PC71BM-based devices, the DC values are much higher than 0.0054,15 indicating that their corresponding CRI values are unbelievable. However, the D-BDT-SQ:PC71BM-based device shows a very close value to 0.0054, hence, the high CRI value of this device is considered meaningful.
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.8b08878. Synthetic methods and characterization of IDPSQ (PDF)
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AUTHOR INFORMATION
Corresponding Authors
*E-mail:
[email protected] (T.S.). *E-mail:
[email protected] (H.S.). F
DOI: 10.1021/acsami.8b08878 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX
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[email protected] (Y.H.). *E-mail:
[email protected] (J.K.).
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ORCID
Daobin Yang: 0000-0001-5611-8209 Hisahiro Sasabe: 0000-0002-1312-0111 Satoru Ohisa: 0000-0002-2916-7512 Yan Huang: 0000-0002-6559-6234 Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS The authors acknowledge the financial support by the Japan Science and Technology Agency (JST) and Ministry of Education, Culture, Sports, Science and Technology (MEXT) through the Center of Innovation (COI) Program, and the National Natural Science Foundation of China (Project no. 51573108). They thank Yukimasa Fukada for discussing the calculation of CIE color coordinates.
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DOI: 10.1021/acsami.8b08878 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX
