The Influence Of The Processing Parameters On The Photovoltaic Properties Of CH₃NH₃PbI₃ Perovskite Film By Solution Methods

Organic-inorganic CH₃NH₃PbI₃ perovskite is a new-type organic metal compound semiconductor material, which has attracted great attention in the field of thin film solar cells for some excellent photoelectric properties, such as, high absorption coefficient and carriers density, great carriers mobility, long diffusion length, low excition binding energy, narrow band gap, etc. The power conversion efficiency of perovskite thin film solar cells have achieved great improvement with the sequential improvement of CH₃NH₃PbI₃ thin film preparation methods and techniques. Many research results indicate the power conversion efficiency of perovskite solar cells not only depend on the design structure but more critical to the perovskite thin film quality. Hence, high-quality perovskite thin film is the basis for high performance photovoltaic devices. In this master's degree paper, on the basis of summary and analysis of published works, we choose the new fabrication techniques of high-quality perovskite thin film by solution methods as the breakthrough point and put forward new research approaches to overcome these problems.This dissertation titled “The influence of the processing parameters on the photovoltaic properties of CH₃NH₃PbI₃ perovskite film by solution methods” focuses on the fabrication techniques by solution fabrication methods and investigation of perovskite thin film as well as the photovoltaic properties of planar heterojunction perovskite solar cells. Mainly works and results are as following:?1? Highly pure phase CH₃NH₃PbI₃ perovskite thin films were successfully fabricated by an improved two-step sequential deposition technique. The influence of different heating rate on photovoltaic performance of perovskite thin films for planar heterojunction with TiO₂ films were particularly investigated under annealing process. The experimental results show that the heating rate for annealing process has a great influence on the surface morphology, grain size and compactness of perovskite films. At a moderate heating rate of 3 °C/min, we obtained high-quality perovskite thin films with smoother surface morphology, perfect compact structure and larger average grain size. The high-quality perovskite thin films had enhanced light absorption and higher charge carriers extraction efficiency, and were further assembled into planar heterojunction perovskite solar cells with FTO/TiO₂/CH₃NH₃PbI₃/P3HT/Au structure achieving an improved power conversion efficiency of 5.95 %.?2? An effective solvent sealed natural drying?SND? pretreatment was successfully introduced for forming a satisfactory crystalline porous iodide?PbI₂? precursor film, high-quality CH₃NH₃PbI₃ perovskite thin film and high performance FTO/TiO₂/CH₃NH₃PbI₃/P3HT/Au planar heterojunction perovskite solar cells. The influence of SND pretreated time on the PbI₂ precursor film and porous morphology structure as well as the perovskite films after conversion reaction and device performance were comparatively investigated in detail. The results revealed that the PbI₂ precursor film after 10 min pretreatment could make the perovskite device achieve the optimal power conversion efficiency of 8.6 %, significantly increased up to 95.5 % and 28.4 % compared to without pretreatment or traditional treatment. The results show that high-quality perovskite thin film, including large grain size, good crystallinity and appropriate passivation treatment is critical in improving the efficiency of perovskite solar cells. Hence, our work further verifies that the porous PbI₂ precursor film have great significance on perovskite thin film fabrication as well as the devices performance.