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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]

While 2D Ruddlesden‐Popper (RP) perovskites exhibit attractive opto‐electronic properties and stability for use in perovskite solar cells (PSCs), their complicated film‐forming processes often induce a non‐negligible level of defects that significantly undermine the power conversion efficiency (PCE) and stability of PSCs. Here, the use of two organic ammonium salts with the same chain length, namely monoammonium (butylammonium iodide, BAI) and diammonium (1,4‐butanediamine dihydroiodide, BDAI2) for surface defect passivation of RP‐2D perovskite films of (AA)2MA4Pb5I16 (n = 5) are reported. It is found that the diammonium BDAI2 not only effectively reduces the defect density (similarly to using monoammonium BAI) but forms a Dion‐Jacobson (DJ) 2D structure to enhance interfacial charge extraction and suppress surface charge recombination. As a result, a boosted PCE of 18.34% has been obtained with a high open‐circuit voltage of 1.24 V. Owing to the enhanced structural integrity of the DJ phase, the RP‐2D/DJ‐2D perovskite heterojunction films exhibit supreme material robustness, which translates to the impressive environmental stability of devices, showing nearly zero‐degradation of the efficiency after 800 h of continuous thermal aging (60 °C) for 800 h. This work enriches the fundamental understanding of the impacts of the DJ‐2D structure on the surface properties of 2D perovskites. [ABSTRACT FROM AUTHOR]

Quasi‐2D perovskites have received wide attention in photovoltaics owing to their excellent materials robustness and merits in the device stability. However, the highest power conversion efficiency (PCE) reported on quasi‐2D perovskite solar cells (PSCs) still lags those of the 3D counterparts, mainly caused by the relatively high voltage loss. Here, a study is presented on the mitigation of voltage loss in quasi‐2D PSCs via usage of thermal‐aged precursor solutions (TAPSs). Based on the (AA)2MA4Pb5I16 (n = 5) quasi‐2D perovskite absorber with a bandgap of ≈1.60 eV, a record‐high open‐circuit voltage of 1.24 V is obtained, resulting in boosting the PCE to 18.68%. The enhanced photovoltaic performance afforded by TAPS is attributed to the thermal‐aged solution processing that triggers colloidal aggregations to reduce the nucleation sites inside the solution. As a result, formation of high‐quality perovskite films featuring compact morphology, preferential crystal orientation, and lowered trap density is allowed. Of importance, with the improved film quality, the corrosion of Ag electrode induced by ion migrations is effectively restrained, which leads to a satisfactory storage stability with <2% degradation after 1200 h under nitrogen environment without encapsulation. [ABSTRACT FROM AUTHOR]

Organic–inorganic hybrid quasi‐2D perovskites have shown excellent stability for perovskite solar cells (PSCs), while the poor charge transport in quasi‐2D perovskites significantly undermines their power conversion efficiency (PCE). Here, studies on water‐controlled crystal growth of quasi‐2D perovskites are presented to achieve high‐efficiency solar cells. It is demonstrated that the (BA)2MA4Pb5I16‐based PSCs (n = 5) processed with water‐containing precursors display an increased short‐circuit current density (Jsc) of 19.01 mA cm−2 and PCE over 15%. The enhanced performance is attributed to synergetic growths of the 3D and 2D phase components aided by the formed hydration (MAI∙H2O), leading to modulations on the crystal orientation and phase distribution of various n‐value components, which facilitate interphase charge transfer and charge sweepout throughout the device. The water‐assisted crystallization is further applied to triple cation‐based (BA)2(MA0.8FA0.15Cs0.05)4Pb5I16 quasi‐2D perovskites, which generate a remarkable PCE of 18.04%. Despite the presence of water in the precursors, the devices exhibit a satisfactory thermal stability with the PCE degradation <15% under continuous thermal aging at 60 °C for over 500 h. [ABSTRACT FROM AUTHOR]

Understanding the factors that limit the performance of perovskite solar cells (PSCs) can be enriched by detailed temperature (T)‐dependent studies. Based on p‐i‐n type PSCs with prototype methylammonium lead triiodide (MAPbI3) perovskite absorbers, T‐dependent photovoltaic properties are explored and negative T‐coefficients for the three device parameters (VOC, JSC, and FF) are observed within a wide low T‐range, leading to a maximum power conversion efficiency (PCE) of 21.4% with an impressive fill factor (FF) approaching 82% at 220 K. These T‐behaviors are explained by the enhanced interfacial charge transfer, reduced charge trapping with suppressed nonradiative recombination and narrowed optical bandgap at lower T. By comparing the T‐dependent device behaviors based on MAPbI3 devices containing a PASP passivation layer, enhanced PCE at room temperature is observed but different tendencies showing attenuating T‐dependencies of JSC and FF, which eventually leads to nearly T‐invariable PCEs. These results indicate that charge extraction with the utilized all‐organic charge transporting layers is not a limiting factor for low‐T device operation, meanwhile the trap passivation layer of choice can play a role in the T‐dependent photovoltaic properties and thus needs to be considered for PSCs operating in a temperature‐variable environment. [ABSTRACT FROM AUTHOR]