The Fabrication Of CH₃NH₃PbI₃ Thin Film And Its Application In Mesoporous Solar Cells

Organic/inorganic trihalide lead-based perovskite solar cell is a new type of thin-film solar cell.It has many advantages,for example,high efficiency,low cost,plenty of raw materials,which is called the new star of the field of solar cell.At present,its power conversion efficiency has reached 22.1%,which has already matched the demand of commercialization.The key point of perovskite solar cell is the absorption layer material:CH₃NH₃PbI₃.It has a suitable band gap of 1.55 eV and its absorption coefficient is several orders of magnitude larger than the traditional material.Only a small thickness of film is enough to meet the needs of light absorption.CH3NH3PbI3 has weakly bounded excitons with long carrier diffusion length.And it has the property of bipolar transportation.High qualified CH3NH3PbI3 thin film is the key point of achieving high efficiency solar cells.Common CH₃NH₃PbI₃ thin film fabrication methods are spin coating method,dual-source evaporation method,vapor assisted solution method and so on.Among these methods,spin coating method is the most convenient and effective one.Most researchers at home and abroad use this technique to do science research.The efficiency of perovskite solar cells is improved very fast.However,some basic detail problems in CH3NH3PbI3 thin film fabrication still need systematic study.It makes a big difference to look for new simple effective ways to manufacture perovskite thin film.This article is based on the material system of CH₃NH₃PbI₃,using the technique of two step spin coating,systematically studied the effects of preparation technologies on the morphology,crystallinity and light absorption properties of CH₃NH₃PbI₃ thin film.We explored the different fabrication methods of PbI₂ film and CH₃NH₃PbI₃ thin film and the CH₃NH₃PbI₃ film annealing methods.The quality of the film is improved.We applied the improvedCH3NH3PbI3thinfilmtothe FTO/bl-TiO₂/mp-TiO₂/CH₃NH₃PbI₃/Spiro-OMeTAD/Au structured solar cells and studied the photovoltaic properties.The main works are as follow:?1?Using the two-step spin-coating method to manufacture the CH₃NH₃PbI₃ thin film.We studied the different MAI/IPA precursor concentration effects on the CH₃NH₃PbI₃thin film morphology and crystallinity.We find when the MAI/IPA precursor concentration is at 50 mg/mL,the CH3NH3PbI3 perovskite film presents a smooth and uniform surface.Then we explored the effects of different combined solvent volume ratio of PbI₂ precursor on the CH3NH3PbI3 film morphology and crystallinity.The results reveal the solvent volume ratio at4:1 is the best at which the CH₃NH₃PbI₃ film shows an even surface.We also studied the anti-solvent effect on the morphology of CH₃NH₃PbI₃ thin film.The results show that anti-solvent method improves the morphology,crystallinity and light absorption properties.Thus,improves the power conversion efficiency.?2?We take ladder temperature annealing method,diethyl ether extraction method and DMF solvent vapor annealing method to treat PbI₂ film and apply the CH₃NH₃PbI₃ perovskite film of three different PbI₂ treatments to the solar cells.The mechanism of these three methods are as follow:ladder temperature annealing facilitates formation of the PbI₂ film.Diethyl ether extraction method promotes the removal of DMF and DMSO,which also benefits the formation of the PbI2 film.DMF solvent vapor annealing method promotes the cluster of PbI₂ to recrystallize.All these three techniques are beneficial to the formation of PbI₂ film and CH₃NH₃PbI₃ thin film.Thus their power conversion efficiencies are also improved.?3?Using two-step method to fabricate the CH₃NH₃PbI₃ thin film.Then we apply DMF and alcohol solvent annealing to the perovskite film and set a control group.The research results demonstrate that DMF and alcohol vapor annealing treatment facilitate the growth of CH₃NH₃PbI₃ crystal,increase the grain size and improve the CH₃NH₃PbI₃ film crystallinity.Using this technique of solvent-vapor annealing,Our perovskite solar cell achieves a higher short circuit current density of 15.59 mA/cm²,an open circuit voltage of 1.054 V,a fill factor of 0.612 and a conversion efficiency of 11.07%.