Preparation And Performance Studies Of Solution-Processed Planar Heterojunction Perovskite Solar Cells

Organic-inorganic perovskite solar cells developed rapidly in the past few years,and have overwhelmed many other contemporary photovoltaic technologies.With the outstanding advantages of high power conversion efficiency,low-temperature and simple manufacturing process,perovskite solar cells show great potential to commecialization.The ability of the perovskite light-absorbing layer to capture sunlight,generate and extract charge carriers efficiently,contributes significantly to obtain high performance solar cell devices.In order to prepare a high-performing perovskite layer,improving the crystal quality of thin films and reducing the defect density of perovskite have been shown as an effective way.This work studies perovskite thin films prepared by differing solution-casting methods,i.e.one-step spray coating and two-step spin coating.The purity of the precursor material,as well as additive engineering techniques,were investigated in order to ascertain their effects on the quality of the perovskite thin films,and photovoltaic performance of relevant devices.This work is divided into the following parts:（1）Spray-coated perovskite solar cells with grain sizes up to 400 microns,and photovoltaic performance comparable to spin-coated devices,were successfully fabircated by optimizing the one-step ultrasonic spraying process.With a ITO/PEDOT:PSS/MAPbI₃/PC₆₁BM/Ag inverted structure,the spray-coated perovskite device achieved a maximum efficiency of 12.6%from reverse scan,and there is no obvious hysteresis.The effects of PbI₂ purity on the formation and properties of perovskite thin films and the photovoltaic properties of the resulting solar cells were studied,by employing the one-step spray-coating and two-step spin-coating methods respectively.It was found that improving the PbI₂ purity could improve the morphology of the spray-coated perovskite films,increasing the crystallinity and crystal size whilst reducing grain boundaries,which contributes to reducing the defect density and carrier recombination within the device,thereby improving device efficiency.The high PbI₂ purity guarantees a high efficiency of the devices fabricated by the two-step spin-coating method,but the extent of reducing efficiency is relatively less when reduing the PbI₂ purity.This manifests the importance of a high PbI₂ purity in fabricating perovskite solar cells by employing a large-scale fabrication method,e.g.spray coating.（2）1,3-2 aminoguanidine hydrochloride（DAGCl）was introduced as an additive during the two-step solution-casting of MAPbI₃.The appropriate amount of DAGCl in the perovskite precursor could increase the grain size of the perovskite film,prolong carrier lifetime and reduce carrier recombination,thereby improve device efficiency.The device made with the addition of DAGCl in the perovskite layer,using the structure of ITO/PolyTPD/MAPbI₃/PC₆₁BM/ZrAcac/Ag,achieved the highest power conversion efficiency of 20.3%compared to 19.1%from the reference device.The positive effect of DAGCl additive to tune the morphology and efficiency is also met in perovskite solar cells prepared by ultrasonic spray coating,and suggests the universal effect of DAGCl additive to improve device performance via different solution casting approaches.