Dual‐Strategy Tailoring Molecular Structures of Dopant‐Free Hole Transport Materials for Efficient and Stable Perovskite Solar Cells

DTTP-ThSO is designed by dual-strategy method combining conjugate engineering and side chain engineering, which can construct six-membered ring through S⋅⋅⋅O noncovalent conformation lock. DTTP-ThSO exhibits high hole mobility, good energy level matching, and strong defect passivation ability. The dopant-free DTTP-ThSO-based PSCs achieve an impressive PCE of 23.3 % with an FF of 82.3 %, among the highest performance n-i-p PSCs with dopant-free HTMs.

Abstract

Dopant-free hole transport materials (HTMs) are ideal materials for highly efficient and stable n-i-p perovskite solar cells (PSCs), but most current design strategies for tailoring the molecular structures of HTMs are limited to single strategy. Herein, four HTMs based on dithienothiophenepyrrole (DTTP) core are devised through dual-strategy methods combining conjugate engineering and side chain engineering. DTTP-ThSO with ester alkyl chain that can form six-membered ring by the S⋅⋅⋅O noncovalent conformation lock with thiophene in the backbone shows good planarity, high-quality film, matching energy level and high hole mobility, as well as strong defect passivation ability. Consequently, a remarkable power conversion efficiency (PCE) of 23.3 % with a nice long-term stability is achieved by dopant-free DTTP-ThSO-based PSCs, representing one of the highest values for un-doped organic HTMs based PSCs. Especially, the fill factor (FF) of 82.3 % is the highest value for dopant-free small molecular HTMs-based n-i-p PSCs to date. Moreover, DTTP-ThSO-based devices have achieved an excellent PCE of 20.9 % in large-area (1.01 cm²) devices. This work clearly elucidates the structure-performance relationships of HTMs and offers a practical dual-strategy approach to designing dopant-free HTMs for high-performance PSCs.

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