High-performance all-polymer solar cells enabled by a novel low bandgap non-fully conjugated polymer acceptor

The non-fully conjugated polymer as a new class of acceptor materials has shown some advantages over its small molecular counterpart when used in photoactive layers for all-polymer solar cells(all-PSCs),despite a low power conversion efficiency(PCE)caused by its narrow absorption spectra.Herein,a novel non-fully conjugated polymer acceptor PFY-2TS with a low bandgap of~1.40 eV was developed,via polymerizing a largeπ-fused small molecule acceptor(SMA)building block(namely YBO)with a non-conjugated thioalkyl linkage.Compared with its precursor YBO,PFY-2TS retains a similar low bandgap but a higher LUMO level.Moreover,compared with the structural analog of YBO-based fully conjugated polymer acceptor PFY-DTC,PFY-2TS shows a similar absorption spectrum and electron mobility,but significantly different molecular crystallinity and aggregation properties,which results in optimal blend morphology with a polymer donor PBDB-T and physical processes of the device in all-PSCs.As a result,PFY-2TS-based all-PSCs achieved a PCE of 12.31%with a small energy loss of 0.56 eV enabled by the reduced non-radiative energy loss(0.24 eV),which is better than that of 11.08%for the PFY-DTC-based ones.Our work clearly demonstrated that non-fully conjugated polymers as a new class of acceptor materials are very promising for the development of high-performance all-PSCs.