Regulating the electron transporting properties of indacenodithiophene derivatives for perovskite solar cells with PCEs up to 19.51%

Abstract

Indacenodithiophene-based multi-fused aromatic structures have been largely developed as non-fullerene acceptors for organic solar cells and gained great successes. However, they are less explored as electron transporting materials for perovskite solar cells, despite their compatible energy levels and good electron mobilities. In this work, three n-type non-fullerene acceptors are applied as electron transporting materials in inverted perovskite solar cells (PSCs). All three compounds are of a rigid ladder-type structure with different conjugation lengths of the central multi-fused ring and end-capped with 2-(6-oxo-5,6-dihydro-4H-cyclopenta[c]thiophen-4-ylidene)malononitrile (CPTCN). Consequently, IDTCN, IDT6CN and ITCPTC with five, six and seven fused-rings are obtained. The longest conjugation length in ITCPTC leads to the enhanced electron mobility, and electron extraction and electron transporting ability. In addition, the ITCPTC molecule shows a predominant “face-on” orientation in neat films, which is favorable for charge transport in PSCs. As a result, inverted PSCs using the ITCPTC ETL deliver a champion efficiency of 17.42%, while the devices with IDT6CN and IDTCN exhibit a lower efficiency of 15.56% and 13.86%. Moreover, the non-fullerene acceptors also perform well when applied as interfacial materials in PSCs; ITCPTC delivers a remarkable efficiency of 19.51%, with a FF value as high as 82%. This work reveals the great potential of indacenodithiophene-based non-fullerene acceptors as efficient electron transporting materials for PSCs. The investigation towards the structure–electron transporting property relationship could provide insights for future design of efficient ETMs for inverted PSCs.