The high polarity of water molecules inevitably causes the decomposition of perovskites. We retard the degradation by introducing an ultrathin ALD–Al ₂ O ₃ layer, which has almost no negative effect on performance.

The PCE of perovskite solar cell based on ALD-ZnO reached 13.1%; CH₃NH₃Cl promoted the formation of CH₃NH₃PbI₃ on 70 °C-ALD-ZnO films.

GQDs at grain boundaries effectively bond to CH₃NH₃PbI₃ so as to passivate the hanging bonds and rapidly extract electrons from CH₃NH₃PbI₃.

Balancing the high power conversion efficiency (PCE) and long-term stability of organic–inorganic hybrid perovskite solar cells (Pero-SCs) is a challenging factor for the commercialization of solar cells. Herein, a cost-effective and widely available water-soluble additive, polyvinyl alcohol (PVA), has been adopted to improve the film quality of CH₃NH₃PbI₃ and enhance the efficiency and long-term tolerance to humidity. A PCE of 17.4% has been achieved for the device with PVA, showing an 11.6% increase compared to those of the devices without the additive. Most importantly, the unencapsulated devices retain over 90% of their initial efficiency even after 30 days in a high humidity environment (90% relative humidity), exhibiting greater humidity tolerance and superior stability. Our studies present a simple solution-based approach to fabricate high efficiency solar cells with long-term stability under high humidity conditions, potentially revealing new methods for the mass production of Pero-SCs.