Design and photovoltaic characterization of dialkylthio benzo[1,2-b:4,5-b′]dithiophene polymers with different accepting units

Abstract

Three dialkylthio benzo[1,2-b:4,5-b′]dithiophene (S-BDT) based polymers have been developed using different accepting units to tune their bandgaps. The polymer:PC₇₁BM solar cells achieved the highest power conversion efficiency (PCE) of 4.51% without any post-treatment (such as annealing and solvent additive) in conventional single-cell devices. Joint photophysical, electrical and computational studies on the polymer based solar cells revealed the considerable impact of molecular planarity on polymer design. The polymer:PC₇₁BM devices processed with 1,8-diiodooctane for improving their morphology afforded an improved PCE value of 5.63%, with a V_oc of 0.83, a J_sc of 10.24 mA cm⁻² and a FF of 66.3%.