Organic metal halide Solar Panel Application is a solar cell with all-solid perovskite structure as the light-absorbing material. The material has the advantages of simple preparation process and low cost.The structure of the perovskite material is ABX3, where A is the organic cation, B is the metal ion and X is the halogen group. In this structure, the metal B atom is located at the center of the cubic cell, the halogen X atom is located in the cube face, and the organic cation A is at the cube vertex position (Fig. 1). The perovskite structure is more stable and is conducive to the diffusion migration of defects than in the structure with coplanar and coplanar connections.
In the perovskite structure used for high efficiency solar cells, the A site is usually an organic cation such as HC (NH2) 2+ (FA +) or CH3NH3 + (MA +), and its main role is to maintain charge balance in the lattice The size of the A ion can change the size of the bandgap. When the A ion radius increases, lattice expansion, resulting in a corresponding increase in energy gap, the absorption side of the red shift, resulting in greater short-circuit current and about 16% of the high battery conversion efficiency. Metal ion B is usually Pb ion, Pb has good stability, but because of toxicity, it is often replaced by Ge, Sn, Ti. Sn, for example, Sn-X-Sn bond angle greater than Pb, narrower energy gap , ASnX3 shows a high open circuit voltage and good photoelectric characteristics, the voltage loss is very small. However, in order to solve the stability problem, Pb and Sn are combined with a certain proportion, which reduces the instability caused by Sn, and obtains higher conversion efficiency. In the same family element, the smaller the atomic number is, the less the element stability is. The halogen group X is usually iodine, bromine and chlorine, and the perovskite solar cells with iodine groups are less effective in mechanical properties (such as elasticity, strength, etc.) than those with bromine groups. The electron absorption spectra are broadened from Cl to I in turn, and the red shift of the energy gap increases successively due to the increase of the atomic weight and the covalent effect of the metal ion B bond. ABX3-type organic-inorganic halides have different structures at different temperatures.
After the incident light passes through the glass, the photons whose energy is larger than the bandgap width are absorbed to produce excitons, and then the excitons are separated from the perovskite absorption layer into cavities and electrons and injected into the transport material, respectively, Is from the perovskite material into the hole transport material, the electron injection is from the perovskite material into the electron transport material (usually titanium dioxide film). Based on this, perovskite has two types of structures: mesostructure and planar heterojunction structure. Mesoscopic perovskite solar cells are based on dye-sensitized solar cells (DSSCs) developed, and DSSCs similar structure: calcium Titanium ore structure nanocrystals attached to the mesoporous structure of the oxide (such as TiO2) skeleton material, hole transport material deposited on its surface, the three together as a hole transport layer . In this structure, the mesoporous oxide (TiO2) is both a skeleton material and also serves to transmit electrons. The planar heterojunction structure separates the perovskite structure material and is sandwiched between the hole transport material and the electron transport material (Fig. 2 (b)). The excitons are separated in the sandwich perovskite material, which can transfer holes and electrons at the same time.
The crystallographic orientation of the perovskite structure material also affects the efficiency of the battery. Docampo et al. Found that when the solution was immersed, or after the CH3NH3I and PbCl2 were mixed, the subsequent heat treatment resulted in a larger battery short circuit and higher conversion efficiency The The change in this process is that the long axis of the perovskite structure tends to be parallel to the substrate to form anisotropy. The more obvious the anisotropy is, the better the battery performance, so the crystallographic orientation of the perovskite material is also Get one of the key directions for superior performance.