Lithium bis­(trifluoromethanesulfonyl)­imide (Li-TFSI) additive is widely employed to improve the hole mobility of the hole-transporting layer (HTL) in perovskite solar cells (PSCs). However, the hygroscopic nature of Li-TFSI is not beneficial to the long-term stability of PSCs. Herein, a new more water-resistant Li-PFSI is used to replace Li-TFSI. As a result, the best power conversion efficiency (PCE) of 22.14% is achieved for Li-PFSI-treated PSCs, exceeding that of the control cell with Li-TFSI (20.25%). Importantly, the Li-PFSI-based cell shows impressive environmental and thermal stability. Moreover, we first comparatively investigate the effect of the amount of fluorine substitution in lithium salt (2F for Li-FSI, 6F for Li-TFSI, and 10F for Li-PFSI) on the HTL’s physical properties and their photovoltaic performance in PSCs. We found that more fluorine substitution can improve the HTL charge-carrier transfer and photovoltaic performance in PSCs. Our findings provide key missing information for designing new additives toward efficient and stable PSCs.

Interfacial engineering for passivating perovskite surface defects and reducing nonradiative recombination loss has been proven to be an effective strategy to fabricate highly efficient and stable perovskite solar cells (PSCs). However, the detailed understanding of the original role of interface materials on the charge‐carriers transfer dynamics of electron transport layer (ETL) remains lacking. Herein, a perylene diimide (PDI) was engineered onto perovskite surfaces to afford passivation of undercoordinated surface defects, which correlates this with the improvement of photovoltaic performance and stability of PSCs. Extensively experimental and theoretical studies reveal that PDI molecule can effectively modulate the surface properties of perovskite film through not only interaction of carbonyl groups in PDI with surface defects but also formation of close‐packed superstructure of PDI onto perovskite surfaces. Consequently, the PDI‐treated PSCs exhibits an increase of power conversion efficiency from 19.52% to 22.24% with an excellent stable device maintaining 95% of its initial value for 900 h in ~45% relative humidity. Importantly, transient absorption spectroscopic measurements further provide an evidence for the origin of the improved photovoltaic performance in PDI‐treated PSCs device, in which the modulation of PDI enhanced the electron transfer across ETL interface more efficiently. Our study provides new insights to understand the effect of interfacial material on the charge‐carrier transfer dynamics in PSCs device.

Three cost-effective D-π-D hole transport materials (HTMs) with different π-bridge including biphenyl (SY1), phenanthrene (SY2) and pyrene (SY3) have been synthesized by one-pot reaction with cheap commercially available starting materials...

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