Preparation And Properties Of The Key Component Materials For Perovskite Solar Cells

Organolead halide perovskite solar cells (PSCs) have drawn great attention due to their outstanding merits such as tunable material properties, high power conversion efficiency (PCE), simple preparation technology and very low manufacture costs. In just a few years, the certified device efficiency of PSCs has exceeded 20%, which is comparable to the records of the second generation solar cells, such as CdTe and Cu-In-Ga-Se (CIGS) systems. PSCs have evolved from traditional sensitized solar cell with liquid electrolyte to solid-state sensitized solar cell and to other types of photovoltaic devices, such as,3D heterojunction cells, planar heterojuntion cells (planar thin film cells) and inverse configuration of organic solar cells. For each type of PSCs, it is the research focus to select and optimize their key component materials (such as light-absorbing perovskite materials and electron/hole-transporting materials) to achieve satisfied performance and stability. In this thesis, several different key component materials were used in PSCs with different structures respectively. And both the device performance and application potential were increased by optimizing the preparation methods or technique process for these component materials.(1) For the development of stable and efficient hole-transporting materials (HTMs), polymer PCBTDPP was studied for the first time as HTM in solid-state sensitized solar cells with CH3NH3PbBr3/CH3NH3Pbl3 sensitized mesoporous TO2. It was found that PCBTDPP-based PSCs showed significantly superior photovoltaic performance than typical polymer HTMs (such as P3HT) based cells. It is especially notable that an open circuit voltage (Foe) as high as 1.24 V has been obtained for the CH3NH3PbBr3/PCBTDPP devices. Interestingly, CH3NH3PbI3/PCBTDPP-based PSCs showed efficiency up to 5.6%iwith excellent long-term stability. The conversion efficiency had experienced no obvious decline subject to storage of 1100 h under ambient dark condition.(2) For the development of high performance 1D electron-transporting materials (ETMs) in PSCs, rutile TiO2 nanorod and nanocone arrays were successfully grown on FTO substrate with an acid-free hydrothermal method. The effects of the growth parameters on the morphology of 1D TiO2 arrays were studied in detail. It was revealed that the length, diameter and density of the TiO2 nanorod/nanocone arrays could be effectively adjusted by varying the growth time or the initial concentration of reactants, making them very suitable for the filling of perovskite materials. The as-made 1D TiO2 arrays were further evaluated as ETMs in 3D heterojuction PSCs successfully. Nanocone-based PSCs showed much higher PCEs than nanorod-based ones because of the more open structure and better electron injection/transport characteristics.(3) For the advanced preparation technics of uniform and large-area perovskite thin films, a novel gas-solid reaction, i. e., direct contact and intercalation process (DCIP) was developed. With DCIP method, uniform and compact CH3NH3PbI3 film could be effectively prepared on substrates in large area, resulting in solar cells with PCEs up to 16.0% for small devices, and large devices with area of 1.00 cm2 made on 5.0 cm × 5.0 cm perovskite films displayed an impressive efficiency up to 12.6%, indicative of the up-scalability of DCIP in fabricating high-performance PSCs.(4) To improve the quality and device performance of perovskite thin films based on one-step solution process, DMF/GBL mixed with DMSO was used as solvents for peorvskite solution spin-coated on TiO2 compact layers. The ratios of mixed solvents were studied and optimized in detail, which had great influence on the morphology and properties of perovskite thin film. The optimized planar-structured PSCs made from 40 vol.% DMF mixed with DMSO showed micrometer-scale large grains and less grain boundaries, leading to less charge recombination during the process of charge transport. A highest PCE of 16.9% and a stabilized efficiency of 15.0% were achieved, which was higher than the reported performance data of PSCs with similar device structures.