Suppressing trap states and energy loss by optimizing vertical phase distribution through ternary strategy in organic solar cells

Suppressing the trap-state density and the energy loss via ternary strategy was demonstrated. Favorable vertical phase distribution with donors (acceptors) accumulated (depleted) at the interface of active layer and charge extraction layer can be obtained by introducing appropriate amount of polymer acceptor N2200 into the systems of PBDB-T:IT-M and PBDB-TF:Y6. In addition, N2200 is gradiently distributed in the vertical direction in the ternary blend film. Various measurements were carried out to study the effects of N2200 on the binary systems. It was found that the optimized morphology especially in vertical direction can significantly decrease the trap state density of the binary blend films, which is beneficial for the charge transport and collection. All these features enable an obvious decrease in charge recombination in both PBDB-T:IT-M and PBDB-TF:Y6 based organic solar cells (OSCs), and power conversion efficiencies (PCEs) of 12.5% and 16.42% were obtained for the ternary OSCs, respectively. This work indicates that it is an effective method to suppress the trap state density and thus improve the device performance through ternary strategy.