Investigation On Nickel Oxide Hole Transport Layer In High-efficiency Perovskite Solar Cells

Organic-inorganic hybrid perovskite materials have been widely concerned because of their high absorption coefficient,optimal band gap and high defect tolerance.In just a few years,the power conversion efficiency(PCE)of perovskite solar cells(PSC)increased from 3.8%to over 25.2%,and it has been considered as the most promising photovoltaic device.In perovskite solar cells,the choice of materials for the hole transport layer(HTL),the perovskite absorption layer,and the electron transport layer(ETL),as well as the defects and charge distribution in the interface between layers can significantly affect the carrier generation and recombination,and also affect the film formation of each other,thereby affecting the performance of perovskite solar cells.This work mainly studies the interface characteristics between the nickel oxide hole transport layer and the perovskite absorption layer.The methods of doping modification and adding a modification layer are used to optimize charge transport,passivate interface defects,adjust energy level arrangement,and increase the crystallinity of perovskite films,thereby improving the performance of perovskite solar cells.The main research contents and research results are as follows:1.The effect of lithium(Li)and cobalt(Co)co-doped NiOx hole transport layer on the performance of reverse planar heterojunction PSC devices was investigated.Compared with the undoped NiOx film and Li-doped NiOx HTL,the addition of a certain amount of Li and Co can further improve the conductivity and hole mobility of the NiOx film.Therefore,the PCE of PSC device based on NiOx HTL doped with 10%Li and 5%Co was greatly improved from 17.4%to 20.1%.In addition,the short-circuit current density(Jsc)increased from 22.7mA·cm-2 to 23.8mA·cm-2,the open circuit voltage(Voc)of increased from 1.05V to 1.09V,and the fill factor(FF)increased from 0.73 to 0.78.These results indicate that co-doping of Li and Co for NiOx HTL can be an effective strategy to improve PSC performance.2.Because the interface state in PSCs is the main factor affecting the stability and performance of the device,interface engineering including strain engineering is an effective method to solve this problem.In this work,by inserting a Cesium Bromide(CsBr)buffer layer between the NiOx HTL and the perovskite layer,the interfacial stress caused by lattice mismatch can be relieved and more regular perovskite crystal growth can be induced.Both experimental and theoretical results showed that the addition of the CsBr buffer layer optimizes the interface between the perovskite absorber layer and the NiOx HTL,reduces interface defects and traps,and enhances the hole extraction/transfer.The PCE of optimal device after optimization researches up to 19.7%which is significantly higher than the efficiency of the device without the CsBr buffer layer(17.7%).Meantime,the device stability is also improved.