Study On The Influence Of Sodium Halide Additives On The Performance Of CsPbI₂Br Perovskite Solar Cells

The development and utilization of renewable energy is the theme of energy field in today's society.Among many renewable energy sources,solar energy stands out due to its wide distribution,high utilization efficiency and environmental friendliness.Solar cells are devices to utilize solar energy and have been developed for three generations.Among them,perovskite solar cells are favored by researchers due to their excellent optoelectronic performance and low manufacturing cost.The photoelectric conversion efficiency(PCE)of organic-inorganic hybrid perovskite solar cells has reached 25.7%,but its commercialization process is seriously hindered due to the high temperature resistance of organic cations.Replacing organic cations with inorganic Cs⁺can greatly improve the thermal stability,so all-inorganic perovskite solar cells have also emerged.Among photoactive materials of all-inorganic perovskite solar cells,CsPbI₂Br has become the research hotspot owing to its suitable bandgap and good stability.However,due to the poor quality of the CsPbI₂Br film,the PCE of the CsPbI₂Br perovskite solar cells is still far behind that of the organic-inorganic hybrid perovskite solar cells.In order to improve the quality of the CsPbI₂Br thin film and improve the PCE of the CsPbI₂Br solar cells,this paper uses easily available and low-cost sodium halide(Na Cl and Na Br)additives to modify and optimize CsPbI₂Br thin film to improve the PCE of solar cells,the research content is as follows:(1)The basic structure of the CsPbI₂Br solar cell in this paper is ITO/Sn O₂/CsPbI₂Br/P3HT/Ag.During film formation,the spin coating speed and annealing temperature have an important impact on the CsPbI₂Br film quality,and thus affect the performance of solar cells.In this paper,the optimal spin coating speed and the annealing temperature were explored,and the next work was carried out on this basis.(2)The use of additives can effectively improve the film quality and enhance the performance of solar cells.In this paper,Na Cl was used as an additive to optimize the performance of CsPbI₂Br perovskite solar cells.The study found that the device performance is improved because Na Cl effectively improve the quality of the CsPbI₂Br film,passivate the defects of the CsPbI₂Br film,optimize the interfacial contact,and promote the separation and extraction of the carriers,thereby reducing energy loss.Based on the above optimization,the PCE of the CsPbI₂Br all-inorganic perovskite solar cell reached 14.22%,and the open-circuit voltage reached 1.24 V.Although the introduction of Na Cl can improve the performance of solar cells,the introduction of Cl^-shrinks the unit cell structure of CsPbI₂Br,which destroys the stability of the device.(3)To solve the problem of the degradation of device stability caused by the introduction of Cl^-,we used Na Br as an additive to modify the CsPbI₂Br film.The study found that Na Br can not only improve the film quality,enhance the device optoelectronic properties.Meanwhile,it can effectively improve the moisture resistance of the CsPbI₂Br film.And the diffusion of Ag ions can be inhibited due to the Na Br-modified high-quality CsPbI₂Br film.The PCE of the finally optimized CsPbI₂Br all-inorganic perovskite solar cell reached 14.70%,and the stability was good.Moreover,the improved operation stability for the unencapsulated devices with the Na Br-modified CsPbI₂Br layers is observed,i.e.,?90.1%retention of the initial power conversion efficiency after 200 h aging in air with the relative humidity of 30%-40%,while the control device was decomposed between 80 and 120 h.