Research On The Performance Optimization And Stability Of Perovskite Solar Cells

Since 2009,the photoelectric conversion efficiency(PCE)of perovskite solar cells has developed rapidly,but the device stability is not satisfactory.Perovskite materials are easily decomposed under the effect of water,oxygen,heat,light and electricity,which seriously affect the stability of the device and hinder its further development.This paper is aimed to find a way to improve the stability of PSCs,the high-quality electron transport layer was firstly obtained,then the properties of the perovskite layers and the interfaces between the perovskite layer and the hole transport layer were further improved,the relationship between the optical and electrical properties of all the functional layers and the stability of the PSCs were investigated.Finally,the carrier recombination and transportion mechanism were deeply understood.It provided a simple way to achieve the coordination optimization of the efficiency and stability of PSCs.(1)In view of the poor conductivity,low electron mobility,and many defects of tin oxide electron transport materials.The water-soluble carbon nano-dots(CNDs)was synthesized through hydrothermal method,the synthesized CNDs were mixed with SnO2 to prepare the SnO2:CNDs electron transport layer.The optical properties,Fermi level,conductivity,defect states density,carrier concentration and mobility of SnO2 thin films were improved with the introduction of CNDs,in addition,the interfacial contact and carrier transport were further enhanced in the perovskite device with SnO2:CNDs electron transport layer.The device with SnO2:CNDs reached a high PCE of 20.03%and a steady-state PCE of 19.83%with negligible hysteresis.The UV light stability,thermal stability and storage stability of the perovskite device were significantly improved.(2)In view of the disadvantages of small grain,many grain boundaries and uncontrollable thin film growth for the one-step preparation method of perovskite film,thiourea(TU)was introduced into perovskite precursor solution to fabricate the MAPI3 perovskite thin films,the coordination behavior between TU and PbI2 was discovered in crystallizing nucleation process of perovskite films.With the incorporation of TU,the perovskite films were obtained with large grain size,high crystallinity and optimization growth orientation,the grain size of perovskite films was increased from 200nm to 1.5?m.The optimal PCE of the perovskite device was 19.80%and the stable output efficiency was 18.60%,and the storage stability of perovskite device was significantly improved.(3)In view of the disadvantages of many grain boundaries and defects in perovskite film,guanidine(Gua)was used to treat the surface of perovskite film.Gua cation could exchange with MA cation on surface of MAPbI3 and insert into the perovskite lattice structure through secondary annealing process,then the secondary growth of perovskite films and passivation of surface defects could be realized with the formation of(Guai-xMAx)PbI3 perovskite on the surface of MAPbI3 perovskite.Finally,with the treatment of GuaI solution,the PCE of PSCs increased from 15.98%to 18.54%,the stable output efficiency of the device reached 18.10%with negligible hysteresis,the humidity stability and storage stability of the perovskite device were significantly improved.(4)In view of the disadvantages of many dangling bond,a large number of defects,hydrophilic state exposed on the surface of perovskite films,cetyl-trimethyl ammonium bromide(CTAB)was used to treat the surface of the perovskite films.On one hand,the long carbon chain in the CTAB could improve the hydrophobicity of perovskite films and protect perovskite films from moisture,on the other hand,with the interfacial modification of CTAB,the defects and non-radiative recombination could be reduced,and the carrier transport could be enhanced.In addition,the diffusion behavior of Br-in perovskite films was also analyzed.Based on the interfacial modification of CTAB,The PCE of 18.95%and the steady-state output efficiency of 18.11%were reached,the high humidity stability and storage stability of the device were significantly improved.