Semitransparent Blue, Green, and Red Organic Solar Cells Using Color Filtering Electrodes

Abstract

protocols that tailor the absorption spectrum of the active material. [1][2][3][4][5][6] While such efforts have resulted in a library of active materials, they have also presented challenges for commercial viability due to the different processes and costs associated with employing distinct active materials to display different colors. Their use has also resulted in varied performances among devices of different colors, adding to the difficulty for practical implementation. Furthermore, challenges in organic synthesis have limited the achievable types of color and their spectral purity. In this work, we introduce a strategy that enables a single active material that absorbs uniformly across the visible range to display different colors with high spectral purity and consistent device performances through the implementation of a color filtering (CF) electrode. The electrode consists of a Ag-TiO x -Ag Fabry-Perot (FP) resonant cavity, where the thickness of the TiO x layer determines the spectral position of the transmission peak and the inner Ag layer functions as an electrical contact. The electrode also functions as a mirror for all wavelengths of light except that within the resonant band (i.e., the spectral transparency window) of the CF. Therefore, light that has not been selectively transmitted may reflect back into the active material, contributing to additional charge generation. This implies that the short-circuit current density, which is largely a function of the optical absorption, must be higher for a CF-integrated OPV compared to a transparent OPV, under the condition that the two devices show similar peak transmission efficiencies.The use of photonic structures as optical filters in OPVs or inorganic solar cells has been previously reported in the form of distributed Bragg reflectors, [7][8][9] photonic arrays, [10][11][12] and plasmonic resonators. [13][14][15] While such filters enable various colors to be transmitted or reflected through tuning of the characteristic dimension of the filter components, in many cases they suffer from increased fabrication costs and duration because of the structural complexity. Moreover, photonic structures employing low-loss dielectrics exhibit poor electrical conductivity, precluding their use as an electrode. Finally, the structural anisotropy intrinsic to 1D or 3D photonic structures can result in asymmetric responses for light incident from above and below the device. Such behavior can complicate design schemes for creating bidirectional colored windows.Colorful, semitransparent organic photovoltaic cells (OPVs) are increasing in demand due to their applicability in aesthetically fashioned powergenerating windows. The traditional method of generating different colors in OPVs has been through employing different active materials exhibiting distinct absorption spectra. This can complicate fabrication processes for production and cause deviations in device performance among differently colored OPVs. Herein, semitransparent and colorful OPVs with a single broadban...

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“…[ 84 ] Kim et al applied a Ag/TiO x /Ag metal/dielectric/metal (MDM) electrode to obtain PTB7‐Th:PC 71 BM ST‐OPVs having values of T MAX of greater than 25% and PCEs of up to 4.5%. [ 146 ] Zhong et al embedded ultrathin Au as an interlayer between the active layer and the Ag/WO 3 /Ag structure, resulting in PCEs of up to 9% and values of T MAX in the range 10–25% for various color gamut samples (Figure 4b). [ 147 ] Shafian et al applied solution‐processed TiO 2 –AcAc as the dielectric layer (Figure 4c); [ 148 ] wet‐processing of the dielectric layer contributed to the facile fabrication of their ST‐OPVs.…”