High‐Efficiency Ternary Polymer Solar Cells Based on Intense FRET Energy Transfer Process

A new wide band gap polymer PBDTPS‐FTAZ is designed and synthesized to form complementary absorption with non‐fullerene acceptor 3,9‐bis(2‐methylene‐(3‐(1,1‐dicyanomethylene)indanone)‐5,5,11,11‐tetrakis(4‐hexylphenyl)dithieno[2,3‐d':2,3'‐d']‐s‐indaceno[1,2‐b:5,6‐b'] dithiophene (ITIC). The optimized device utilizing PBDTPS‐FTAZ:ITIC as active layer exhibits a power conversion efficiency (PCE) of 8.53%. The external quantum efficiency (EQE) spectrum indicates that the binary‐blend device suffers relatively low photo response in the 450–550 nm region. Therefore, the fullerene derivative PC 71 BM and a wide band gap donor polymer P( p ‐FDBND‐2T) with the absorption region of 450–550 nm are added to the PBDTPS‐FTAZ:ITIC system to construct ternary blend solar cell, respectively. As a result, ternary‐blend solar cells based on two configurations (D:A 1 :A 2 and D 1 :D 2 :A) both deliver high PCE over 10% using the conventional device structure. Interestingly, the D 1 :D 2 :A type ternary solar cell exhibits a higher open circuit voltage ( V OC ) along with an intense energy transfer process regardless of the undesirable energy level alignment and reached a high PCE of 11.46%.