Preparation And Performance Of Perovskite Solar Cells CH₃NH₃PbI₃ Absorption Layer Prepared By Two-Step Sequential Deposition Procedure

Perovskite solar cells based on organolead trihalides such as represent an emergency photovoltaic technology, attracting much interest in the scientific community. Perovskite light absorption layer plays a critical role in the working process of the perovskite solar cells. This paper reports CH₃NH₃PbI₃ thin films without PbI₂ residue prepared via a two-step sequential deposition procedure. We optimized the fabrication parameters and studied the influence on photovoltaic performance of CH3NH3PI3 thin films.First, we prepared CH₃NH₃PbI₃ film by two-step sequential deposition method, then annealed the film at 75 ℃ for 30min. This paper studied the influence of fabrication parameters on photovoltaic performance. The thin film is in agreement with the tragonal perovskite structured CH₃NH₃PbI₃ crystals in this paper. We reported that no PbI₂ residue, high crystallinity CH₃NH₃PbI₃ thin films can be deposited by a two-step sequential deposition method involving dipping in a solution of CH₃NH₃I followed immediately by annealing at 75 ℃. When the solution temperature is 20,40,60 and 80 ℃, the optical band gap is 1.473,1.5,1.469 and 1.447 eV, respectively, which meet the best absorption range of solar 1.45-1.5 eV. The absorption coefficients of the films were above 4*104 cm-1 in the temperature of the dipping solution at 40 ℃. Moreover, the quality of CH₃NH₃PbI₃ thin films can remarkably be promoted by improving the crystallinity of PbI₂ film, which is attributed to adding additives of chlorobenzene or isopropyl alcohol.To further optimize the performance of CH₃NH₃PbI₃ thin films, we pre-spin-coat CH₃NH₃I film between mesoporous TiO₂ layer and PbI₂ film and analyze the effects on their properties. The results show that the pre-spin-coating CH₃NH₃I film ensures no PbI₂ phase, and the surface morphology is more smooth, the plate structure disappears, the CH₃NH₃PbI₃ film grows well. For CH₃NH₃PbI₃ thin films, with the increase of dipping temperature, optical absorption behavior increases firstly and then decreases. And thin films have good optical absorption properties in the UV visible range, the transmittance is below 8%, and the absorption coefficient is above 4*104 cm-1. While the CH₃NH₃PbI₃ thin film prepared by the impregnation temperature at 40 ℃, the surface porosity of the film is decreased. When the PbI₂ is 1.2 mol/1, the perovskite thin film prepared by the pre-spin-coating CH₃NH₃I has good uniformity and density, and the band gap is 1.508 eV, which is close to the optical band gap of the ideal solar cell absorption layer.