Substrate heating is the most common method for controlling crystallization during spray coating. However, due to poor controllability during substrate heating, the sprayed films have variable thicknesses and rich pores, which limit the efficiency of the device. Here, hot air blowing was applied to spray coating to promote the crystallization of perovskite films under ambient conditions. Upon employing a hot air blowing method that stimulated uniformly distributed nuclei growth, the pinhole-free and thickness-controllable perovskite film was prepared. This enabled more reproducible high-quality perovskite films to achieve a power conversion efficiency of 13.5% and obtain a stabilized power output of >12% in ambient conditions.

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The best research-cell efficiency for quantum dot solar cells has boosted from 11.6 to 18.1% within 5 years due to the evolution of perovskite quantum dots (PQDs) that are being intensively developed along with the flourishing of perovskite thin-film photovoltaics. During the fabrication of PQD devices, as far as we know, methyl acetate (MeOAc) is an ineluctable solvent in ligand exchange for producing highly efficient solar cells. Nevertheless, the reproducibility for PQD solar cells using MeOAc treatment is poor since it has to make a trade-off between removing long-chain organic ligands for high charge transport and keeping them for the stabilization of the black crystal phase. Herein, we demonstrate the degree of MeOAc treatment on CsPbI3 PQD solid films in detail and clarify that MeOAc treatment is able to not only remove the oleyl ligands for promoting the charge transport but also passivate the surface defects in the CsPbI3 PQD solid films. It is noted that immoderate MeOAc treatment could induce the formation of the δ-phase, leading to the degradation of device performance. After locating the balance for MeOAc treatment, the CsPbI3 PQD solar cells are fabricated and optimized without using any additional modifications except MeOAc treatment, and these additive-free devices possess a conversion efficiency surpassing 12%.

The development of perovskite solar cells (PSCs) has progressed rapidly because of their high efficiency and low cost. The performance of PSCs is predominantly determined by the quality of the perovskite films, which is controlled by the fabrication process. The comprehensive and in-depth understanding of the nucleation, crystallization, and growth process are imperative for the further advancement of large-scale manufacturing of high-quality perovskite films. In this work, the simple process parameters of perovskite thin films were systematically optimized at ambient air, such as containing the thickness of the perovskite thin film, the anti-solvent bath, and the thermal annealing time. Through these simple processes, the wet film, solvent volatilization, and crystallization of perovskite films can be controlled and optimized. After optimizing the spraying conditions, the champion power conversion efficiency (PCE) of the PSCs achieved 20.6% (reverse scan) and had little hysteresis in the current density−voltage (J− V). In addition, the unsealed device retained 85% of its original PCE and showed excellent long-term stability after 650 h of storage in the drying tower.

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