Perovskite solar cells (PSCs) have achieved unprecedented power conversion efficiency improvements, and further development is stepping to industrialization. In terms of industrial manufacturing, simplifying the solar cell structure is critical in both fabrication process design and cost control. Due to the bipolar charge transport nature of perovskites, the elimination of the charge carrier transport layer is possible. Herein, EMIMPF6 ionic liquid is incorporated into the perovskite film to modulate the energy‐level alignment and the charge transfer kinetics, demonstrating a high‐performance electron transport layer‐free (ETL‐free) PSC. The integrated EMIMPF6 assisted the internal charge collection and favored the interfacial charge transfer from perovskite to FTO substrate, contributing to the high performance of ETL‐free PSCs. The ETL‐free PSCs showed a conversion efficiency of 16.2%, which is comparable with its conventional counterpart. This work provides a solution to simplify the PSC structure and would have an impact on designing a scalable manufacturing process for PSCs.

SnO2 films as a promising electron transport layer (ETL) have been widely used in planar-type perovskite solar cells to achieve an impressive improvement in the conversion efficiency. However, compared with a mesoporous ETL, the interfacial charge carrier transfer of the SnO2 ETL is severely limited due to the issues of oxygen vacancy defects and crystal lattice mismatch between SnO2 and the perovskite, which generally leads to the growth of randomly stacked and porous perovskite layers and subsequently impacts the charge transport and transfer properties. In this work, we developed a facile approach by inducing a bifunctional molecule, β-alanine, into the SnO2 ETL, which can serve as a bridge to modulate the interfacial charge transfer and the perovskite crystallization kinetics. Benefited by the interfacial β-alanine, we grew a highly orientational perovskite layer that exhibited superior charge transport properties. Meanwhile, the β-alanine caused an intimate connection between the perovskite and SnO2 to enhance the interfacial charge transfer. As a result, the power conversion efficiency (PCE) of the β-alanine-modified device achieved a much-improved value of 19.67% and showed high reproducibility. This work provides a way for developing a high-performance ETL toward the scalable fabrication of highly efficient PSCs.

Formamidinium (FA)-based perovskites remained state-of-the-art in the field of perovskite solar cells (PSCs) owing to the exceptional absorption and carrier transport properties, while the transition from photoactive (α-) to photoinactive (δ-FAPbI 3 ) phase is the impediment that causes performance degradation and thus limits the deployment of FA-based PSCs. The unfavorable phase transition originates from tensile strain in the FAPbI 3 crystal lattice, which undergoes structural reorganization for lattice strain balancing. In this work, we found that the ionic liquid (IL) could be used as the strain coordinator to balance the lattice strain for stability improvement of FAPbI 3 perovskite. We theoretically studied the electronic coupling between IL and FAPbI 3 and unraveled the originality of the IL-induced compressive strain. The strain-relaxed α-FAPbI 3 by IL showed robust stability against environmental factors, which can withstand ambient aging for 40 days without any phase transition or decomposition. Moreover, the strain-relaxed perovskite films showed a lower trap density and resulted in conversion efficiency improvement from 18.27 to 19.88%. Based on this novel strain engineering strategy, the unencapsulated PSCs maintained 90% of their initial efficiency under ambient-air aging for 50 days.

Two-dimensional (2D) metal halide perovskites can co-construct with the state-of-the-art three-dimensional (3D) perovskite analogs to form 2D/3D perovskite heterojunction architectures, which enables the photovoltaic devices to deliver higher energy conversion efficiency and near-commercial stability. However, the question remains as to whether any type of 2D perovskite, i.e., RP, DJ, or ACI perovskites, is workable with a 3D analog to outperform the pristine 3D perovskites. Here, we investigate the structural and electronic properties of distinct types of 2D/3D perovskite heterojunctions based on first-principles calculations. We selected a 3D FAPbI 3 perovskite combined with representative 2D RP, DJ, and ACI perovskites to construct a series of 2D/3D perovskite heterojunctions and analyzed the carrier transport kinetics and charge recombination of each heterojunction. The results indicate that RP-PbI, DJ-FAI, and ACI-FAI heterojunctions exhibited favorable transport and separation of photogenerated carriers, but the RP-PbI and ACI-FAI heterojunctions appear to possess greater potential for photovoltaic applications than the DJ-FAI heterojunction due to relatively fewer recombination losses. Moreover, based on the direction of photogenerated carrier transport at the heterojunction, we predict that RP-PbI would be superior to DJ-FAI for conventional 2D/3D devices and that the ACI-FAI heterojunction is expected to well function in the inverted 2D/3D devices.