Soochow University and others have made new progress in all-perovskite stacked solar cells

On July 21, 2022, Beijing time, Nature Energy, a top international academic journal, published online the collaborative team of Professor Li Xiaofeng of Soochow University, Professor Zhao Dewei of Sichuan University and Dr. Fu Fan of the Swiss Federal Institute of Materials Science and Technology (EMPA) entitled “A universal close-space annealing strategy towards high-quality perovskite.” Absorbers enabling efficient all-perovskite tandem solar cells”.

The collaborative team proposed a strategy for preparing high-quality perovskite crystalline films by a limited-area annealing method, and the method was universal to different components of perovskite films, and finally achieved an all-perovskite stack solar cell with an efficiency of more than 25%.

Associate Professor Wang Changhuan of Soochow University is the first author of the paper, Professor Li Xiaofeng of Soochow University, Professor Zhao Dewei of Sichuan University and Dr. Fu Fan of EMPA switzerland are the corresponding authors of the paper.

The development of efficient and clean photovoltaics can promote the restructuring of China’s energy industry and help the country achieve the long-term goals of “carbon neutrality” and “carbon peaking”. Organic and inorganic hybrid perovskite materials have excellent optoelectronic properties and have made important progress in the field of photoelectric conversion. Constructing a laminated solar cell based on perovskite materials and breaking through the efficiency limit of single junction photovoltaic devices is an effective way to improve the efficiency of perovskite photovoltaics. All-perovskite laminated solar cells contain different band gaps of perovskite light-absorbing materials, because different components will affect the crystallization process and characteristics of perovskite materials, resulting in uncontrollable film growth process and poor crystallization quality and other issues. At present, there is no universal crystallization regulation method that can be applied to the high-quality preparation of different components of perovskite films at the same time. Therefore, the development of a universal crystallization regulation method is of great significance for the preparation of high-quality perovskite films and the realization of high-performance single junction and multi-junction stacked perovskite solar cells.

In this work, the collaborative team is based on the existing technology of all-perovskite laminated batteries (Nat. Energy 2017, 2, 17018;Nat. Energy 2018, 3, 1093), developed a universal perovskite film crystallization regulation method, which showed good results for improving the quality of different bandgap perovskite films. The perovskite grain size prepared by the Close Space Annealing (CSA) method increased significantly, the carrier life increased significantly, and the defect density decreased significantly, thereby effectively inhibiting non-radiative composites, and finally obtaining high-efficiency single junction wide bandgap and narrow bandgap perovskite cells, so that the efficiency of all-perovskite four-terminal and two-terminal stacked solar cells exceeded 25%.

Figure 1: Schematic diagram of three different ways of conventional annealing, solvent annealing and limited area annealing and perovskite film morphology. The e-plot shows the grain growth process of perovskite thin films under the limited-area annealing mode.

Narrow band gap perovskites contain a large amount of tin, resulting in perovskite films crystallizing too quickly and introducing more defects. The perovskite grain size obtained by the conventional annealing heating process is small and the film quality is poor. Existing solvent annealing methods can improve the quality of perovskite films to a certain extent, but for tin-lead mixed perovskite materials, excessive solvent and crystallization process will damage the uniformity of the absorbent layer and cause a certain amount of holes. The limited-area annealing method reported in this work places the surface of the perovskite intermediate phase perovskite film upside down on the breathable diaphragm, and the resulting tin-lead perovskite grain size increases significantly, reaching the micron level, while the surface is dense and defect-free, and the uniformity is good. The main mechanism for improving the photoelectric properties of perovskite thin films by the limited-area annealing method is to dissolve the original grain boundaries with the help of residual solvents, and fuse adjacent grains to obtain large-size grains and achieve high-quality film preparation.

Figure 2: Performance characterization of single-junction narrow bandgap perovskite solar cells.

Figure 3: Performance characterization of single-junction wide-bandgap perovskite solar cells. a, b, c indicate conventional annealing, solvent annealing and limited-area annealing perovskite films, respectively.

Figure 4: Performance of all-perovskite laminated solar cells.

By using the limited-area annealing method, a high-quality perovskite absorbing layer was prepared, and the efficiency of the four-terminal stacked solar cells obtained was 25.15%, and the steady-state output power was about 25%.” The efficiency of the obtained all-perovskite stacked batteries reached 25.05%, and the steady-state output efficiency of the device was 24.5%, which was higher than that of conventional annealed stacked batteries (22.85%). The unpackaged laminated device operates continuously in an inert gas glove box for 450 hours with a maximum power output of 90% of the original value, showing good operating stability. (Source: Science Network)

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