PCDTBT8‐Doped PffBT4T‐2OD‐Based Ternary Solar Cells with Enhanced Open‐Circuit Voltage, Fill Factor, and Charge Separation Efficiency

The effect of a medium bandgap polymer doped into conventional binary heterojunction solar cells is investigated for ternary solar cells, which display different characteristics compared with traditional materials. First, the charge separation and recombination at the multi‐interface (double donors / single acceptor) and the charge transport between different phases are simulated to reveal the competition mechanism of electron transfer and insights into the merits and demerits of a hole transport layer with medium and narrow band gaps. Second, global modeling of performance for PCDTBT8‐doped PffBT4T‐2OD‐based ternary solar cells is established to evaluate the crucial parameters (open‐circuit voltage ( V OC ), short‐circuit current ( J SC ), fill factor ( FF ), and power conversion efficiency (PCE)) related to the experiment. The results demonstrate that the orbital energy levels, absorption peak, excited‐state, fluorescence lifetimes, and hole transportability are tunable upon the medium bandgap polymer doping process. The electron transfer process for the multi‐interface is enhanced by doping different bandgap polymers compared with a single interface, which contributes to the energy match and multistep jump mechanism. Ternary solar cells based on the doped polymer exhibit better V OC , FF , and PCE with weakened J SC . The theoretical calculations are in excellent agreement with experimental results. The global investigation of ternary solar cells can be used to interpret experiments and is viewed as an effective method for screening high‐performance solar cells.