The design of dithieno[3,2-b:2′,3′-d]pyrrole organic photovoltaic materials for high-efficiency organic/perovskite solar cells

Organic solar cells (OSCs) and perovskite solar cells (PVSCs) are emerging photovoltaic technologies with solution-processability and performance that can feasibly be tuned via the molecular design of key organic photovoltaic materials (OPMs). With the innovation of fused-ring electron acceptors (FREAs), the power conversion efficiency (PCE) values of OSCs have been pushed as high as 18%. Meanwhile, molecular hole-transport materials (HTMs) have demonstrated promising advantages compared to the widely used material spiro-OMeTAD, allowing PCEs of over 20% to be realized in dopant-free PVSCs. In this review, we provide updates on progress related to the design and use of dithieno[3,2-b:2 ',3 '-d]pyrrole (DTP)-based OPMs as symmetric/asymmetric FREAs and dopant-free HTMs for obtaining record-high power conversion efficiencies and stable solar cells since 2016, with the objective of giving insightful views into material design and device construction strategies to boost photovoltaic performance. Strategies relating to judicious molecular designs are demonstrated for fine-tuning the electronic structures, crystallinity, thermal properties, and molecular orientations of DTP-based OPMs. Structure-property correlations are discussed in detail. New device engineering and processing strategies tailored to DTP-OPM-based solar cells are emphasized. Finally, we briefly summarize original designs of DTP-derived OPMs to address the challenging issues facing emerging solar cells and highlight key considerations relating to the development of new efficient OPMs.