Low Energy Gap Triphenylamine–Heteropentacene–Dicyanovinyl Triad for Solution-Processed Bulk-Heterojunction Solar Cells

Abstract

A low bandgap D–D–A (D = donor; A = acceptor) type conjugated molecular triad TPA-SN5-DCV has been implemented in solution-processed organic solar cells using PC71BM as acceptor. The molecule showed a narrow optical energy gap of 1.59 eV, and a broad absorption spectrum ranging from 350 to 750 nm. Cyclic voltammetry measurements were used to estimate the highest occupied molecular orbital and lowest unoccupied molecular orbital energy levels and are −5.10 and −3.53 eV, respectively. After the optimization of the donor and acceptor (PC71BM) weight ratio, the device based on as cast TPA-SN5-DCV:PC71BM (1:2) active layer exhibited overall PCE of 3.34%, which was improved to 6.31% using 0.3 vol % 1,8-diiodooctane (DIO) as solvent additive (SA). Further optimization of the DIO-treated active layer via thermal annealing (TA) resulted in a markedly improved PCE of 7.26%. The enhancement in PCE after either SA or SA + TA treatment is largely accredited to the increase in both JSC and FF, which is associated with ...