The Study On The Stability Of Formamidinium-based Perovskite Solar Cell

Driven by the advance of materials science,the field of perovskite photovoltaics has developed rapidly.Recently,the power conversion efficiency of single-junction perovskite solar has achieved 25.2%.Although the highest efficiency of formamidinium based perovskite solar cells(PSCs)have reached 75%of the Shockley-Queisser limit efficiency,which showed a potential to compete with silicon cells,its commercialization is still hindered by the device stability.How to suppress the phase instability of formamidinium based perovskite is a key strategy to improve the stability of PSCs on the on hand,on the other hand,finding a solution to avoid the stability problem induced by charge transporting layer is also a crucial issue for whole device stability.In order to fabricate efficient and stable formamidinium based PSCs,improving the perovskite intrinsic phase instability and substitution with stable charge transporting layer have been taken into consideration.In this thesis,achievements about improved operational stability of formamidinium based PSCs have been obtained:(1)Based on sequential deposition method,cesium iodide has been incorporated with Pb I₂precursor to enhance the FAPb I₃ perovskite film quality and stability.SEM mappings and XRD results have revealed that the FAPb I₃ perovskite with CsI additive showed better crystallinity,enlarged grain sizes and fewer grain boundaries as well.Furthermore,the photoelectric property tests suggested the carrier life time of CsI induced perovskite was prolonged over 1?s,which proved decreased defects density of perovskite.Via optimal decent CsI induced and promoted deposition process,the fill factor of device was significantly improved,and the champion device with a steady 22.2%efficiency was obtained.Moreover,the stability of perovskite itself was enhanced greatly as well.The best device without encapsulation has still delivered a steady output of 22%after a storage of 37 days in a controlled 26%relative humid environment.(2)Spiro-OMe TAD,which has functioned as hole transporting material in many highly efficient normal structure PSCs,is limited for its poor thermal stability and also potential degradation of perovskite caused by its additives.In inverted structure,due to hydrophobic property and organic nature of PTAA,the PTAA based inverted PSCs also suffer from stability perovskite deposition problem.Nickel oxide(NiOx)as a transparent p-type metal oxide semiconductor with excellent thermal,photo and chemical stability,is one of the promising hole transporting materials applied in inverted PSCs.For the purpose of improving the hole extraction ability of NiOx film by solution process,polyvinyl pyrrolidone(PVP)has been incorporated into the NiOx precursor.The results suggested the NiOx with PVP additive showed more uniform surface and decreased charge trap density,which was beneficial to the extraction efficiency at the interface of NiOx/perovskite.With the assisting NiOx film forming by the PVP polymer,the open-circuit voltage of NiOx based device has been improved.Finally,the efficiency of inverted device was boosted to 20%based on modified NiOx with respect to that on pristine NiOx.