Improved efficiency in fullerene and non-fullerene polymer solar cells having an interdigitated interface with the electron transport layer

Abstract

We report improved efficiency in fullerene and non-fullerene polymer solar cells utilizing an interdigitated interface between the photoactive layer and the PFN-OX electron transport layer (ETL). This interdigitated interface is formed in situ during the solution casting process of the photoactive layer on the blend films made of electron-transporting PFN-OX and template materials of either semi-conducting 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis((4-hexylphenyl)-dithieno[2,3-d:2′,3′-d′]-s-indaceno[1,2-b:5,6-b′]dithiophene) (ITIC) or insulating polystyrene (PS). Compared to the devices having a planar interface between PFN-OX and the photoactive layer, devices with an interdigitated interface templated by ITIC increased the efficiency of PTB7-Th:PC₇₁BM solar cells from 9.3% to 10.4%, with the device having an interdigitated interface templated by PS exhibiting a PCE of 9.9%. PTB7-Th:ITIC non-fullerene solar cells employing this ITIC-templated interdigitated PFN-OX ETL exhibited an enhanced PCE from 7.4% to 8.3%. Interfacial charge transport studies support that favorable electrical doping of PFN-OX to ITIC as well as charge transfer between PTB7-Th and ITIC contribute to this superior efficiency enhancement in devices employing an ITIC-templated interdigitated PFN-OX ETL. This work provides a new strategy for constructing a novel ETL to prepare high efficiency polymer solar cells.