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Quasi‐2D perovskite solar cells (PSCs), with impressive stability and tunable optoelectronic properties, have become a promising alternative to 3D PSCs. However, the lack of understanding about rationally promoting the film quality of 2D perovskites has significantly undermined their power conversion efficiency (PCE). Herein, a thermally induced crystallization strategy to process the Dion–Jacobson (DJ) 2D perovskite films based on (BDA)(MA)4Pb5I16 (n = 5) afforded by thermal treatments is reported, realizing high‐quality perovskite films with increased crystallinity and dense structure. The photovoltaic performance of PSCs improved by thermal treatments is found to be mainly attributed to the significantly suppressed nonradiative recombination, more efficient charge generation, and restricted interfacial charge accumulation. As a result, the optimal device processed with thermal treatments produces a high open‐circuit voltage of 1.21 V and a PCE of over 17.6% with suppressed energy loss down to 0.42 eV. Moreover, the treated devices without encapsulation show a satisfactory stability with <20% PCE degradation after 1000 h under maximum power point tracking. The demonstrated strategy in this work offers a promising route for the performance enhancement of 2D DJ PSCs toward realistic energy conversion applications. [ABSTRACT FROM AUTHOR]

Although the photovoltaic performance of perovskite solar cells (PSCs) has reached the commercial standards, the unsatisfactory stability limits their further application. Hydrophobic interface and encapsulation can block the damage of water and oxygen, while the instability induced by intrinsic residual strain remains inevitable. Here, the residual strain in a two‐dimensional (2D) Ruddlesden–Popper (RP) perovskite film is investigated by X‐ray diffraction and atomic force microscopy. It's found that the spacer cations contribute to the residual strain even though they are not in the inorganic cages. Benefited from strain relaxation, the film quality is improved, leading to suppressed recombination, promoted charge transport and enhanced efficiency. More significantly, the strain‐released devices maintain 86 % of the initial efficiency after being kept in air with 85 % relative humidity (RH) for 1080 h, 82 % under maximum power point (MPP) tracking at 50 °C for 804 h and 86 % after continuous heating at 85 °C for 1080 h. [ABSTRACT FROM AUTHOR]

Molecular doping is an effective means to tune the optoelectronic properties of organic semiconductors. Despite its versatility, its application in bulk heterojunction (BHJ) organic solar cells (OSCs) is still limited, especially blend‐cast doping. Difficulties in desolving molecular dopants in weakly polar solvents have led to the formation of undesired structures, with relatively high concentrations of dopants affecting the bicontinuous BHJ morphology. Bilayer OSCs are stacked structures with sequential deposition of donor and acceptor films, which make important contributions to the fine tuning of morphology and balanced charge transport. The sequential deposition of thin films in bilayer devices organically facilitates the sequential doping of pure donor polymers by dopants. The sequential doping of the dopant at the interface between the donor and the acceptor can efficiently improve the carrier mobility and the charge transfer between the donor and the acceptor without damaging the quality of the film, thus improving the device performance efficiently. With three different dopants F4TCNQ, F6TCNNQ, and BCF, sequential interfacial doping in bilayer devices is found to be a versatile and effective method to improve device performance. Making this simple doping strategy promising for high‐performance bilayer OSCs, it is evaluated as a promising alternative to BHJ OSCs. [ABSTRACT FROM AUTHOR]