Efficiency and stability are the two most important factors in commercially scalable solar cells. In spite the high-power conversion efficiencies (PCE), the commercialization of perovskite solar cells (PSC) has been limited due to their low stability under ambient conditions. Environmental factors like moisture, heat, and light can all adversely affect PSC performance and limit device lifetime. In this review, we refer to the literature addressing the moisture induced stability issue of perovskite based solar cells. We present an overview on the moisture stability of the perovskite solar cells and clarify the effect of moisture on different layers in perovskite solar cells and the corresponding degradation process. Then we extend the discussion highlighting the strategies to prevent the moisture induced degradation in hybrid perovskite solar cells. The methods include composition engineering (cation and halide engineering) and interfacial layer engineering/surface passivation. We further summarize the utilization of doping techniques and use of organic/Inorganic passivators. We address methods of producing moisture stable 2D perovskites and admixtures of 2D and 3D perovskites. Lastly, the review highlights research directions focused on improving perovskite stability without compromising power conversion efficiency.

Long-term stability is an essential requirement for perovskite solar cells to be commercially viable. Encapsulating 3D perovskites with 2D perovskite structures is an effective strategy for improving resistance to moisture. However, long-chain alkylammonium cation-based 2D perovskites have been rarely studied in solar cells. Here, we study three different alkyl chain length organic cation-based 2D perovskite coatings for 3D perovskites. The 2D perovskite incorporated solar cells show significant improvement in solar cell stability with limited compromise in solar cell efficiency, with the longest alkyl chain length sample showing only a 20% drop in power conversion efficiency after 6 months at a relative humidity of 25-80%, and could be completely immersed in water for a few minutes before degradation started. The 2D perovskite coating also mitigated non-radiative recombination in the light-absorbing 3D perovskite, leading to an enhancement in the open circuit voltage. These findings suggest that long-chain alkylammonium cation based 2D perovskites can improve the environmental stability of 3D based perovskites without significant losses to device performance. Moisture resistance is vital for commercializing perovskite solar cells. Here, long-chain alkylammonium cation-based 2D perovskites are used to coat 3D perovskite, enabling stable performance for six months with only a 20 % drop in power conversion efficiency.

The hybrid perovskite-based solar cells have achieved photovoltaic efficiencies comparable to that of the silicon-based solar cells; however, the light-absorbing perovskite materials are not stable and undergo rapid degradation in the presence of moisture. There are only a few water-stable 2D perovskite materials that have been explored so far. Keeping this in mind, we incorporated 3 different long-chain alkylammonium cations in 2D perovskites using a generic solution synthesis route where the saturated precursor solution was slowly cooled down to room temperature resulting in the single crystals of the 2D perovskites and studied their optical properties and stability against moisture. The prepared 2D perovskites demonstrated robust stability under ambient conditions as well as resistance to water. The main highlight of the present study is 2D perovskites emit bright green light in the 494-520 nm range even in the presence of water. We anticipate that our results on the water stable perovskite will not only motivate the use of these long alkyl chain cation-based 2D perovskite materials in perovskite solar cells for achieving the prolonged device stability but also for the next generation LEDs and display technologies.