Exploiting Ternary Blends to Accurately Control the Coloration of Semitransparent, Non-Fullerene, Organic Solar Cells

Semitransparent organic solar cells (STOSCs) have received increasing attention due to promising applications such as building-integrated photovoltaics. Successful commercialization requires that STOSCs are aesthetically pleasing as well as having balanced power conversion efficiencies (PCEs) and average visible transmittances (AVTs). Non-fullerene acceptors, which possess excellent electrical/chemical properties, have helped STOSCs to achieve high PCE and AVT; however, research related to modulating color and appearance of STOSCs has lagged behind. Herein, narrow bandgap donor and acceptor (PTB7-Th and IEICO-4F) and ultra-wide bandgap acceptors (T2-ORH and T2-OEHRH) are used to achieve semitransparency and controllable device coloration. Blend films with controllable colors including cyan → blue → purple → reddish purple colors are successfully demonstrated, which are controlled by ratios of IEICO-4F:T2-ORH or IEICO-4F:T2-OEHRH with PTB7-Th. By incorporating semitransparent electrodes (comprising Sb₂O₃/Ag/Sb₂O₃), STOSCs with PCEs of 6–7% are achieved for cyan, aqua, indigo, and purple and ≈4% PCEs for reddish-purple colors, with AVTs in the range of 23–35%. Moreover, optical properties of blend films are studied via absorption and transmission measurements, whereas the range of colors achieved is quantified using commission internationale de l'éclairage (CIE) chromaticity and CIE L * a * b* color space then represented as RGB color models.