Electron Transport Layer Optimization And Structural Design Of Perovskite Solar Cells

Considering the outstanding advantages(e.g.high efficiency,low-cost,flexible application),the metal halide perovskite solar cells(PSCs)have been placed on high expectation to accelerating the process of achieving carbon peaking and carbon neutrality goals.It has become a consensus of researchers to consolidate the basic theory of PSCs technology for improving photovoltaic property and promoting its industrialization.Focusing on the physical mechanism and performance improvement strategy of PSCs,this thesis carried out researches around electron transport layer optimization,cell structure design,heterojunction interfacial structure and carrier transport regulation.The main research works are as follows:(1)Surface micro-structure regulation of SnO2 electron transport layer towards efficient PSCs.Based on the unique chemical properties of the amphoteric oxide,surface alkali-gas erosion(SAE)was proposed to regulate SnO2 surface micro-structure.SAE treatment can reshape the surface crystal morphology and reduce surface roughness,bringing an improved electron mobility and an excellent perovskite/SnO2 interface contact.Besides,-NH2 group absorbed chemically on SnO2 surface during the SAE process can reduce perovskite/SnO2 interface defects.By employing the SAE treatment,the planar PSCs can achieve a PCE over 21%with distinctly improved device stability.This SAE treatment provides a new potential post-treatment method to optimize electron transport layer,such as SnO2,TiO2,ZnO,providing a technical reference for the preparation of efficient PSCs.(2)Effects of TiO2 surface terminal atoms on the heterojunction interface structure and carrier transport.The mechanism of how TiO2 surface oxygen vacancy causes TiO2/MAPbI3 heterojunction interface defect migration and carrier non-radiative recombination was clarified.On the one hand,TiO2 surface oxygen can capture photo-generated electrons as defect states.On the other hand,surface oxygen can induce interfacial perovakite lattice distortion and defect generation through impacting the interface bonding.The surface fluorine passivation was proposed to eliminate TiO2 surface oxygen vacancy,which blocks interface defect migration and reduces interfacial carrier non-radiative recombination loss,leading to MAPI3 based PSCs achieving a PCE of 20.43%.The clarified influence mechanism of TiO2 surface oxygen vacancy on interface structure and carrier transport helps to understand the complex heterojunction interfacial structure and enrich the micro-physical mechanism of PSCs.(3)High-efficiency PSCs via ligand-engineered deposition of TiO2 electron transport layer.In order to simultaneously regulate the properties and surface structure of TiO2 films,a ligand-engineered deposition strategy(LD)based on the coordination ability of ligands was proposed to precisely regulate TiO2 film deposition.Owing to inhibited particle aggregation,decreased interface contact impedance and enhanced electron extraction,the planar PSCs with LD obtain a PCE of 24.81%(certificated 24.5%),the highest value among TiO2-based planar PSCs reported so far.In addition,both the UV and humidity stability of TiO2-based planar PSCs have been distinctly enhanced.Through the LD extension research,the key factors of the ligand materials on the device photovoltaic performance were clarified,which provides a new approach to promote the rapid development of PSCs.(4)Research on efficient planar PSCs with n+/n/n-gradient homojunction.In order to promote the directional carriers transport in perovskite film and reduce the carriers recombination loss,a novel n+/n/n-gradient homojunction and planar PSCs with n+/n/n-gradient homojunction were designed and fabricated.On the basis of maintaining the approached n-type in the middle region of perovskite film,we achieved the perovskite buried surface n+regulation through Li+doping and the perovskite surface n-regulation through involving VD2 into MEO-PEAI,resulting in a perovskite film with n+/n/n-gradient homojunction.Due to the promoted directional carrier transport by n+/n/n-gradient homojunction,planar PSCs with n+/n/n-gradient homojunction achieved a PCE of 24.78%.This novel PSCs with n+/n/n-gradient homojunction provides a new approach to explore the correlation between cell structure and efficiency,and to improve device performance.