Suppressed charge recombination in polymer solar cells based on perylene diimide derivative acceptors via solvent vapor annealing

A singly-linked perylene bisimide dimer (di-PBI) and a low band gap polymer based on dithienocarbazole and isoindigo moieties (P(IID-DTC)) are selected as electron acceptor and donor respectively to fabricate non-fullerene based polymer solar cells. The combination of di-PBI acceptor and P(IID-DTC) donor provides well overlapped absorption profile with solar light in the visible region. The P(IID-DTC):di-PBI blend morphology and its effect on charge transport and recombination have been investigated in detail. The dominant bimolecular recombination in commonly processed P(IID-DTC):di-PBI blend results in a low power conversion efficiency of merely 1%. We find that CH2Cl2 vapor annealing can effectively improve bi-continuous phase separation and boost the electron transport by more than two orders of magnitude due to the detrap of di-PBI molecules from amorphous P(IID-DTC) matrix. More importantly, the dominant bimolecular recombination in the P(IID-DTC): di-PBI blend films is strongly suppressed. Finally, the power conversion efficiency of non-fullerene P(IID-DTC):di-PBI blend solar cell is dramatically improved to 2.95%. (C) 2015 Elsevier B.V. All rights reserved.