Impact of Hole Blocking Layer on the Performance of Solution-Processed Small Molecule Solar Cells

Abstract

In this study, we report the use of poly [(9,9-bis (30- (N,N-dimethylamino) propyl) -2,7-fluorene) -alt-2,7- (9,9-dioctylfluorene) (PFN) as hole blocking layer (HBL) in inverted small-molecule solar cells (SM-iOSCs) using a bulk heterojunction of p-DTS(FBTTh2)2 as donor material and PC70BM as acceptor material. The behavior of these devices is compared to those SM-iOSCs where the HBL was zinc oxide (ZnO). Under 1 sun illumination, devices exhibited a power conversion efficiency (PCE) of 6.75%. It is demonstrated, through analysis of the external quantum efficiency (EQE), abortion UV-vis and atomic force microscopy of the active layer, that charge transport is the limiting factor in the performance of the cells, directly affecting the short circuit current (JSC).