Improving charge transport and suppressing charge recombination in small molecule ternary solar cells via incorporating Bis-PC71BM as a cascade material

Abstract

The development of small molecule organic solar cells (SMOSCs) has attracted considerable attention and achieved comparable power conversion efficiency (PCE) with polymer solar cells. Here, we demonstrate a bulk heterojunction (BHJ) small molecular solar cell with PCE of 5.31% by incorporating Bisadduct of phenyl-C71-butyric acid methyl ester (Bis-PC71BM) as an additional acceptor material into the host binary blend of 2-[4-(N-butyl-N-phenylamino)-2,6-dihydroxyphenyl]-4-[(4-(N-butyl-N-phenylamino)-2,6-dihydroxyphenyl)-2,5-dien-1-ylidene]-3-oxocyclobut-1-en-1-olate (SQ-BP): [6,6]-phenyl C71 butyric acid methyl ester (PC71BM). The short circuit current (JSC) and the fill factor (FF) of ternary SMOSCs are improved by decreasing the carrier recombination loss, increasing exciton dissociation and enhancing the carrier transport. The transient photovoltage (TPV) measurement indicates that the gradient HOMO energy alignment suppresses the charge recombination and leads to the increased charge carrier lifetime in ternary SMOSCs. As a result, the PCE of ternary devices with 5 wt% Bis-PC71BM is about 20% greater than that of SQ-BP: PC71BM based binary SMOSCs.