Semitransparent solar cells with over 12% efficiency based on a new low bandgap fluorinated small molecule acceptor†
Rational molecular design of n-type organic semiconductors with strong near-infrared absorption and visible-light transmittance is critical but still a challenge for application in high efficiency semitransparent organic solar cells (OSCs). Here, by employing fluorinated 2-(2,3-dihydro-3-oxo-1H-inden-1-ylidene)propanedinitrile as an end group, a fused dithienothiophen[3,2-b]-pyrrolobenzotriazole (BTA-core)-based low bandgap electron acceptor, namely Y14, has been designed and synthesized to address this issue. The BTA-core-based non-fullerene acceptor has relatively high electron mobility and a broad absorption from 300 to 1000 nm. The Y14-based single-junction opaque and semitransparent inverted OSCs achieved high power conversion efficiencies (PCEs) of 14.92% and over 12%, respectively. By further optimizing the semitransparent device with additive treatment and thermal annealing, a higher PCE of 12.67% was realized with an average visible transmittance (AVT) of 23.69%. These results demonstrate that this BTA-core-based structure toward non-fullerene acceptors is a universal strategy that is not only suitable for high efficiency OSCs, but also has great potential as an acceptor material in semitransparent devices.