Introduction to Perovskite Solar Cells

The core of the perovskite solar cell structure is the organic metal halide light-absorbing material with the perovskite crystal form (ABX3). In this perovskite ABX3 structure, A is a methylamino group (CH3NH3), B is a metal lead atom, and X is a halogen atom such as chlorine, bromine, and iodine. Currently in high-efficiency perovskite solar cells, the most common perovskite material is lead methylamine iodide (CH3NH3PbI3), which has a band gap of about 1.5 eV, high extinction coefficient, and a few hundred nanometers thick film can adequately absorb Sunlight below 800nm. Moreover, the preparation of this material is simple, and an average film can be obtained by spin coating a solution containing PbI2 and CH3NH3I at room temperature. The above characteristics make the perovskite structure CH3NH3PbI3 not only can absorb visible light and part of the near-infrared light, but also the photogenerated carriers that appear are not easy to recombine, and the energy loss is small. This is the perovskite type solar cell that can achieve high efficiency. The fundamental reason. Because the relatively complex crystal structure has high requirements for the atomic (or group) radius at the three positions A, B, and X, the composition of the perovskite light-absorbing material is relatively fixed. Recently, some research groups replaced the methylamino group at the A position with a methylimid group to narrow the band gap (1.48eV) and obtain a higher photocurrent. Regarding the Pb atom at the B position, when Sn atom replaces Pb atom, there is no report of photoelectric response. For the atom at the X position, halogen atoms such as chlorine, bromine, and iodine can currently be used, but only iodine-based perovskites have a suitable band gap and can achieve high conversion efficiency. In addition to CH3NH3PbI, CH3NHPbI3-xClx is also the most researched material. While keeping the energy level structure basically unchanged, the doping of a small amount of chlorine element can increase the electron mobility, showing more excellent photoelectric performance. However, compared with silicon-based, currently commonly used perovskite light-absorbing materials have insufficient photoshop and range, sensitivity to water and some solvents, and contain heavy metal lead. Therefore, it is very meaningful to find perovskite materials with narrower band gap, better chemical stability, and more environmentally friendly. The development of perovskite thin-film solar cells originated from sensitized solar cells, and based on related technologies accumulated in the past two decades, such as sensitized solar cells, organic solar cells, etc., they have achieved rapid development. The earliest perovskite solar cells used CH3NH3PbI3 sensitized TiO2 photoanode and liquid I3-/I-electrolyte, with an efficiency of only 3.8% (up to 6.5% through optimization). However, since CH3NH3PbI3 is unstable in liquid I3-/I- electrolyte, the stability of the battery is poor. At present, there are very few researches in this area. Using solid hole transport materials (HTM) (such as spiro-OMeTAD, P3HT, etc.) to replace the liquid I3-/I- electrolyte, the battery efficiency has been greatly improved, reaching 16%, which has exceeded the highest efficiency of dye-sensitized solar cells ( 13%), and has good stability. On this basis, H. Snaith et al. replaced the porous scaffold layer n-type semiconductor TiO2 with insulating materials Al2O3 or ZrO2, and assembled them into thin film batteries with hole transport materials, which can also achieve high efficiency (the highest reported efficiency is 15.9%) ). This result declares that this perovskite material CH3NH3PbI3 itself has good electronic conductivity. In principle, the perovskite-type solar cell based on the insulating material support layer has surpassed the traditional sensitization concept, and is a heterojunction solar cell with a mesoscopic superstructure. Furthermore, removing the insulating support layer, based on the average high-quality perovskite film, the planar heterojunction cell prepared can also obtain high efficiency (the highest efficiency reported is 15.7%). On the other hand, in the absence of hole transport materials, perovskite and porous TiO2 form a heterojunction battery, and the battery efficiency has reached 10.5%. In this structure similar to colloidal quantum dot solar cells, the perovskite itself plays a dual role of light absorption and hole transport. In addition, the perovskite material is used as the light-absorbing layer in the structure of organic solar cells, the fullerene derivative PCBM is used as the electron transport layer, and PEDOT:PSS is used as the hole transport layer, which can achieve an efficiency of more than 12%, which exceeds The best result of traditional organic/polymer solar cells. It is worth mentioning that this perovskite solar cell based on the organic solar cell structure can achieve flexibility and roll-to-roll large-scale processing. At present, this flexible perovskite cell has reached a high efficiency of 9.2%. Perovskite materials can achieve a high efficiency of more than 10% in these solar cells with very different structures. In actual use in the future, there may also be a situation where multiple structures coexist and compete. At the same time, in-depth research and understanding of the basic properties of materials and battery working principles are also very important. This will not only help to further improve the performance of perovskite batteries, but also provide people with simpler or more efficient new structure supply ideas. . Disclaimer: Some pictures and content of the articles published on this site are from the Internet, if there is any infringement, please contact to delete. Previous: What are the essentials for lithium battery safety detection