The annealing process for perovskite thin films helps to increase the nucleation rate during film formation, then enhances the grain density, and subsequently promotes the formation of larger and uniformly distributed grains, and ultimately results in high-quality perovskite films, thereby improving the photovoltaic performance of the devices. This article systematically reviews the influencing mechanisms of the annealing process, the types of annealing methods, the process parameters affecting annealing outcomes, and the latest advancements in annealing-free techniques for perovskite thin films. The aim is to provide theoretical foundations and technical references for the preparation of high-quality perovskite films and high-performance PSCs.

By optimizing the uniformity and coverage of perovskite films, the annealing process promotes grain growth and passivates interface defects, thereby enhancing the crystalline quality and optoelectronic properties of the films. While traditional thermal annealing improves film quality to some extent, it can also lead to issues such as pinholes and uneven grain size, which limit the development of PSCs. Consequently, a variety of novel annealing techniques have been developed, including electromagnetic wave (infrared, ultraviolet, laser, and microwave) annealing, ultrasonic annealing, pressure annealing, and solvent annealing. Moreover, precise control of annealing parameters—such as temperature, heating rate, duration, and ambient atmosphere—has been proven critical to optimizing annealing outcomes and directly influences the photovoltaic performance of the devices.

Despite significant progress in annealing techniques, their side effects cannot be overlooked. For instance, high-temperature annealing may trigger perovskite decomposition, some methods are complex and lack reproducibility, and the process incurs additional costs. As a result, annealing-free techniques are gaining attention, as they simplify the fabrication process of PSCs, reduce energy consumption, and lower costs. However, the crystalline quality of annealing-free films still lags behind that of annealed films, warranting further exploration.

Looking ahead, research on the annealing process for perovskite thin films is likely to develop in the following directions:

First, further advancement of in-situ characterization techniques to deeply reveal the microscopic mechanisms of crystal growth during annealing.

Second, leveraging the advantages of machine learning for high-throughput screening of annealing process data to guide the laboratory preparation and industrial application of high-efficiency PSCs.

Third, continued development of novel annealing and annealing-free techniques that balance efficiency and low energy consumption, ensuring high film quality while simplifying the fabrication process and reducing costs.

Currently, the industrialization of perovskite solar cells is becoming increasingly prominent, particularly in perovskite-silicon tandem solar cells. There is an urgent need to address the challenge of achieving uniform crystallization of large-area perovskite films compatible with industrial-grade silicon wafers, which will propel the industrialization of perovskite photovoltaics to a new stage.