Perovskite precursors are generally obtained by mixing halide salts, organic components, inorganic components and additives. Among them, halide salts, organic components and inorganic components are the raw materials for preparing perovskite materials, and additives are substances that regulate the properties of target products. Perovskite films prepared from perovskite precursors can be used as light-absorbing materials for perovskite solar cells (PSCs). The light-absorbing materials of PSC are generally organometallic halide films, which are often prepared from perovskite precursors. The organometallic halide film used in this PSC device has an energy gap of about 1.5 eV and a high extinction coefficient. The perovskite film (organometallic halide films) with a thickness of several hundred nanometers can fully absorb sunlight below 800 nm, and have important application prospects in the field of photoelectric conversion.
Figure 1. The process of preparing perovskite thin films from perovskite precursors
- Preparation of perovskite thin films: In PSC, the quality of the perovskite film determines the upper limit of the energy conversion of the battery. The reasons are as follows: (1) the coverage and density of the perovskite film determine the direct contact probability between the upper and lower electrodes of the PSC and between the hole and electron collection layers, thereby determining the short-circuit degree and carrier recombination opportunity of the device; (2) the crystallinity and grain size of the perovskite film determine the carrier mobility and diffusion length, and affect the carrier collection efficiency; (3) the defect concentration (including composition purity and grain boundary number) of perovskite films determines the recombination degree of carriers, which is related to the collection efficiency of carriers and the size of the photogenerated electric field. It can be seen that the coverage, density, crystallinity, grain size, and crystal defects of perovskite films have a great influence on the photoelectric conversion efficiency of PSC devices. The ideal thin films are characterized by uniform and dense surface morphology, large grain size, and high perovskite crystal phase purity and crystallinity, thereby enhancing the performance and long-term stability of photovoltaic devices. At present, the perovskite growth method used for perovskite thin films is generally a solution method, that is, perovskite crystal thin films are obtained by evaporating the perovskite precursor solution through post-processing solvents. The quality of the precursor liquid determines the film formation quality of the perovskite film. The growth of perovskite nuclei and grains can be regulated by changing the composition of perovskite precursors, thereby obtaining ideal perovskite thin films.
- Minsu Jung, Sang-Geun Ji, Gwisu Kim and Sang Il Seok. Perovskite precursor solution chemistry: from fundamentals to photovoltaic applications[J]. Chem. Soc. Rev., 2019,48, 2011-2038.