The electron transport layer (ETL) is a key component of regular perovskite solar cells to promote the overall charge extraction efficiency and tune the crystallinity of the perovskite layer for better device performance. The authors present a novel protocol of ETL engineering by incorporating a composition of the perovskite precursor, methylammonium chloride (MACl), or formamidine chloride (FACl), into SnO 2 layers, which are then converted into the crystal nuclei of perovskites by reaction with PbI 2 . The SnO 2 -embedded nuclei remarkably improve the morphology and crystallinity of the optically active perovskite layers. The improved ETL-to-perovskite electrical contact and dense packing of large-grained perovskites enhance the carrier mobility and suppress charge recombination. The power conversion efficiency increases from 20.12% (blank device) to 21.87% (21.72%) for devices with MACl (FACl) as an ETL dopant. Moreover, all the precursor-engineered cells exhibit a record-high fill factor (82%).

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Choline chloride as a photosynthesis promoter is important for increasing plant yield, and we have found that it has a similar effect in perovskite solar cells (PSCs). Here, we propose the innovation of using molecular self-assembly methods to produce a choline chloride monolayer on the surface of the SnO 2 ; this monolayer works as a passivation layer that reduces the surface oxygen vacancies and improves the performance of CH 3 NH 3 PbI 3 (MAPbI 3 ) PSCs. The MAPbI 3 PSC based on SnO 2 modified by choline chloride (Chol-SnO 2 ) electron transport layer (ETL) achieves an optimal power conversion efficiency (PCE) of 18.90% under one solar illumination. The PCE is increased by 10−25% compared to the device without modification, and hysteresis is significantly reduced by eliminating the charge accumulation between the interface of the perovskite and ETL. More importantly, the MAPbI 3 PSC based on Chol-SnO 2 ETL exhibits a higher open-circuit voltage (V OC ) of 1.145 V compared to the control device (1.071 V). This work provides a very simple and effective way to improve PSC performance, which has long-term significance for the sustainable development of energy.

Co-modification of an electron transport layer (ETL) with metal oxides and organic molecules can optimize the structure of the ETL and improve the performance of perovskite solar cells (PSCs).

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