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

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(FBTTh 2 ) 2 as donor material and PC 70 BM 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 (J SC ).