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Hole transport materials (HTMs) play an essential role in obtaining efficient and stable perovskite solar cells (PSCs). In particular, PSCs based on dopant-free small molecule hole transport materials (SM-HTMs) have the unique advantages of reproducibility and long-term stability. In this work, we design and synthesis a small molecule, FIMPA-C11, with a D-A-D structure, to serve as a HTM. The corresponding inverted planar PSCs achieve a satisfying efficiency of 17.60%, equivalent to 17.01% of the NiO counterpart, with superior stability and much lower processing temperature. The property and morphology of FIMPA-C11 film make it a better substrate for the crystallization of perovskite absorbing layer. The work enriches the category of HTMs and provides innovation for high-performance dopant-free SM-HTMs in PSCs. [Display omitted] • A small-molecule with D-A-D structure and long alkyl chains was designed and synthesized as a dopant-free HTM for inverted PSCs. • FIMPA-C11 film can reduce the trap density at the HTL/perovskite interface, enhance the carrier migration and improve both efficiency and stability of device. • The device with lower process temperature shows higher PCE and better stability compared to the control device with NiO HTL. [ABSTRACT FROM AUTHOR]

Two perylene diimide (PDI) based polymeric acceptors, PFPDIBT-TT2F and PFPDIT-TT2F, which consist of fused-PDI moieties (FPDIBT and FPDIT) and 3,3′-difluoro-2,2′-bithiophene (TT2F) units, has been designed and synthesized. Compared with the unfused-PDI polymer (PPDI-TT2F) as the control molecule, the influence of structural conformation and π-conjugation extension on the performance of all-polymer solar cells has been investigated. Due to both the extended π-conjugation and the torsional polymer skeleton, the device adopting PFPDIT-TT2F achieved an obviously improved PCE of 5.11% comparing with the devices using the other two polymeric acceptors. This study demonstrates that the fused PDIs bridged by a thiophene enables both extended π-conjugation and twisted molecular conformation, and the latter plays a dominant role in the improvement of device performance. [Display omitted] • Two fused PDI based polymeric acceptors for all-PSCs are designed and synthesized. • Fused PDIs bridged by a thiophene enables both extended π-conjugation and twisted molecular conformation. • Twisted structure plays a dominant role comparing with expansion of π-conjugation. • A rule on the design and selection of the fusing unit for PDI-based polymeric acceptors are proposed as reference. [ABSTRACT FROM AUTHOR]