Low-temperature Solution Processing Of The CsPbI₃ Inorganic Perovskite Solar Cells

Metal halide perovskite materials have excellent photoelectric properties,such as adjustable band gap,high carrier diffusion length,high light absorption coefficient,and low non-radiative recombination,making them very suitable for preparing solar cells.In just 10 years,the photoelectric conversion efficiency（PCE）of perovskite solar cells（PSC）has risen rapidly from the initial 3.8%to the current 25.5%,quickly becoming a research hotspot in the energy field.However,most of the current perovskite batteries are based on organic-inorganic hybrid perovskites,in which organic components are easily volatilized and degraded under high temperature and light.This problem severely restricts the commercial application of perovskite solar cells.Using inorganic cesium（Cs⁺）ions to replace organic cations to form Cs Pb X₃（I,Br,Cl）inorganic perovskite can significantly improve the photothermal stability of the material.Among the inorganic perovskite solar cells,CsPbI₃ has the lowest band gap（～1.7 e V）,can make full use of the solar spectrum,and develops most rapidly.However,the CsPbI₃ perovskite battery film preparation process is relatively immature,the black phase transition temperature of the film is high（>330^oC）,and the Ti O₂ electron transport layer requires high temperature annealing（450^oC）,so the battery preparation process consumes a lot of energy and limits it application in flexible devices.Therefore,it is particularly important to develop a low-temperature solution process suitable for the CsPbI₃ inorganic perovskite solar cells.In response to the above problems,this paper uses dimethylammonium lead iodide（DMAPb I₃）as a precursor to reduce the phase transition temperature,and selects SnO₂nanocrystalline thin film that does not require high-temperature annealing as an electron transport layer,and realizes the CsPbI₃ inorganic perovskite solar cell prepared by the low-temperature solution method.In the preparation process,anti-solvent engineering was used to improve the quality of the CsPbI₃ film,and the SnO₂ electron transport layer was doped and interface modified to improve energy level matching and reduce interface defects,and finally successfully prepared the CsPbI₃ perovskite solar cells with a photoelectric conversion efficiency of 10.46%.In addition to metal electrodes,the entire process flow is based on solution spin coating,and the preparation temperature is below200^oC.It is suitable for flexible devices and has the potential for large-scale industrialization.The main contents are as follows:（1）Aiming at the problem of many holes and poor crystallization of CsPbI₃ film prepared by solution method,anti-solvent engineering was introduced to control the crystallization kinetic behavior of perovskite film.The effects of three different anti-solvents—toluene（Tol）,chlorobenzene（CB）and ethyl acetate（EA）—on the morphology structure and photoelectric properties of CsPbI₃ films were systematically compared.Thanks to its higher polarity and lower boiling point,the green anti-solvent EA can achieve effective extraction of the perovskite precursor solvent.The CsPbI₃ film treated by EA has the best morphology and crystallinity,which greatly reduces the grain boundary defects of the film.（2）Aiming at the problem of energy level mismatch between SnO₂ and CsPbI₃ and low open circuit voltage of the device,by combining polyethyleneimine（PEIE）electrolyte polymer with SnO₂,the electron affinity of SnO₂ is significantly reduced,and the energy level alignment between SnO₂ and CsPbI₃ is achieved.The study found that the PEIE composite can improve the electron extraction ability of SnO₂ film and reduce interface recombination,which will help improve the performance of the device.（3）Aiming at the problem of poor interface quality and serious recombination between SnO₂ and CsPbI₃,Na₂S is introduced to modify the SnO₂ interface,the S^2-in Na₂S can interact with the uncoordinated Pb²⁺in the perovskite film to form a Pb-S bond.At the same time,Na⁺can also enter the surface of the SnO₂ lattice and improve its conductivity.The interaction between the two strengthens the chemical combination at the interface of the perovskite and SnO₂,increases the grain size of the perovskite,and ultimately improves the performance of the device.