Process Optimization And Performance Control Of The Perovskite Solar Cell

Since 2009,perovskite solar cells?PSCs?have attracted wide attention because of its merit of low cost,easy preparation and high efficiency.After 10 years of rapid development,its efficiency has rivaled that of the silicon-based solar cells.However,the structures of most perovskite solar cells with high efficiencies are mesoscopic.Usually the mesoscopic structure of the solar cells needs high temperature sintering and harsh conditions,in addition the hole transport layer and metal electrode material of PSCs are expensive.All mentioned above are barriers for low cost and large scale commercial production of PSCs.Therefore,it is very important to study the low cost carbon electrode PSCs without hole transport layer.At present,the PSCs of carbon electrodes are low efficiency and do not satisfy the commercial standard.In this thesis,the preparation process of PSCs were optimized,including additives was introduced to improve the characteristics of light absorption layer,preparation of low temperature electron transport layer and so on.Then the preparation processes of carbon electrode PSCs were simplified with improving the efficiencies of PSCs.The detailed research contents are listed as follows:1.The preparation processes of PSCs on carbon electrode without hole transport layer were optimized.In two-step preparation processes for perovskite layer,the annealing temperature for perovskite precursor solution and perovskite film were both optimized,as well as the concentration of precursor solution and methyl ammonium iodide solution.A scraping method was used in the preparation of carbon electrode,then pressure was applied on the carbon electrode by a tablet press,which was used to increase the contact area between the carbon electrode and the optical absorption layer.The efficiencies of the PSCs were increased from initial 3.59%to final 8.28%,and the preparation schemes of the PSCs were preliminarily determined.2.The chloride additives were introduced in the preparation of optical absorption layer.In two-step preparation processes for perovskite layer,different amounts of PbCl₂and hydrochloric acid were added to the precursor solution of PbI₂ as chloride additives,respectively.The SEM and XRD results show that perovskite layer can still crystallize well after doping with additives,and the small shifts of XRD peaks prove that chloride additives play their roles.By comparing the UV-visible absorption spectra,it was found that the optical absorption of perovskite layer increased after doping with a small amount of PbCl₂ or concentrated hydrochloric acid.When the doping molar ratio of PbCl₂ to PbI₂ in precursor solution is 1:9,the performance of the PSC is the best one,and the corresponding efficiency reaches 11.35%.The main reason is that appropriate amount of PbCl₂ regulate the crystallization process of the perovskite layer,which produces the bigger perovskite grain,while excessive amount of PbCl₂ brings the residual PbI₂ and worsens the crystallinity.While for concentrated hydrochloric acid,it contains a large amounts of water,so the additional water seriously destroys the perovskite crystallinity and results in low efficiency.3.Among different electronic transport layer materials,titanium dioxide is one of the most commonly used materials in PSCs,but it needs to be sintered at high temperature to improve its electron mobility,which is not suitable for the commercial preparations of PSCs,and not suitable for solar cells with flexible substrates.In this thesis,SnO2 is used as the electron transport layer material in PSCs because SnO2 can be prepared at low temperature and it has higher electron mobility.It was found that SnO₂ films annealed at different temperatures,for example,500 and 180,had similar crystallinity by the SEM and XRD measurements.While SnO₂ films prepared at lower temperature had higher transmittance and stronger optical absorptivity by UV-visible absorption spectra measurement.The J-V curves of the PSCs also show that the efficiency of PSC with SnO2 prepared at low temperature is higher,and this efficiency of PSC is similar to that of the PSC with TiO₂ as the electron transport layer.Therefore,SnO₂ is an effective electron transport layer material that can replace TiO₂.