Matching electron transport layers with a non-halogenated and low synthetic complexity polymer:fullerene blend for efficient outdoor and indoor organic photovoltaics

X. Rodríguez-Martínez, S. Riera-Galindo, J. Cong, T. Österberg, M. Campoy-Quiles and O. Inganäs, J. Mater. Chem. A, 2022, 10, 10768–10779.

The desired attributes of organic photovoltaics (OPV) as a low cost and sustainable energy harvesting technology demand the use of non-chlorinated solvent processing for the photoactive layer (PAL) materials, preferably of low synthetic complexity (SC) and without compromising the power conversion efficiency (PCE). Despite their record PCEs, most donor-acceptor conjugated copolymers in combination with non-fullerene acceptors are still far from up-scaling due to their high cost and SC. Here we present a non-chlorinated and low SC ink formulation for the PAL of organic solar cells, comprising PTQ10 and PC₆₁BM as donor and acceptor materials, respectively, showing a record PCE of 7.5% in blade coated devices under 1 sun; and 19.9% under indoor LED conditions. We further study the compatibility of the PAL with 5 different electron transport layers (ETLs) in inverted architecture. We identify that commercial ZnO-based formulations together with a methanol-based polyethyleneimine-Zn (PEI-Zn) chelated ETL ink are the most suitable interlayers for outdoor conditions, providing fill factors as high as 74% and excellent thickness tolerance (up to 150 nm for the ETL, and >200 nm for the PAL). In indoor environments, SnO₂ shows superior performance as it does not require UV photoactivation. As a result, PTQ10:PC₆₁BM combined with either PEI-Zn or SnO₂, currently positions as a promising system for industrialisation of low cost, multipurpose OPV modules.