Low Temperature Fabrication Of Metal Oxide Charge Transport Layers And Heir Application In Perovskite Solar Cells

Perovskite solar cells（PSCs）grab the attention from all over the world because of its high efficiency,composition tunable,easy process and low cost.The highest efficiency has exceeded 23%,showing great commercial prospect.In regular device,metal oxide is commonly used to collect and transport light induced carriers.However,the fabrication of these metal oxides usually requires high temperature,and the high-temperature sintering process can damage the flexible substrate,which limits their application in flexible devices.Although the low temperature technique has get progress to some extent,most of works focused on small-area cells.In addition,the stability of these cells is poorer than the traditional high-temperature method.Therefore,this thesis mainly focuses on the low-temperature large-area preparation technology of metal oxide charge transport layer and the improvement of device stability in the current study of perovskite solar cells.（1）A simple soft-cover assisted hydrolysis deposition method has been proposed to fabricate high-quality TiO₂ layer at low temperature in order to develop low-temperature preparation techniques for the widely used TiO₂metal oxide electron transport layer.This method is based on the theory of TiCl₄ hydrolysis.A high wettable soft cover is used to spread a small amount of hydrolysate into uniform liquid layer,which greatly enhances the utilization of precursors.A relatively enclosed environment will be formed and prevents the solvents from evaporation,which can provide enough time for the hydrolysis process.By carefully selecting soft cover,optimizing the concentration of hydrolysate and the investigation of film formation,a uniform,compact and nanoneedle structured TiO₂ film is fabricated with rutile phase.Thanks to the pinhole-free TiO₂ film with appropriate thickness and the formation of an intimate junction between the nanocrystalline rutile TiO₂ and the perovskite layer,which could be effective in extracting photogenerated electrons,the device achieves a maximum conversion efficiency of 17.09%.（2）To obtain the perovskite solar module device,the scalable advantages of the soft-cover assisted hydrolytic deposition method were used to prepare a highly uniform large-area TiO₂ thin film at low temperature.The module is assembled through the sophisticated structure design and laser cutting technology based on TiO₂ thin film as an electron transport layer,a high PCE of 14.01%was obtained,which lays a strong basis for the low-temperature fabrication of perovskite modules.（3）In view of the low stability of NiO_x hole transport layer devices prepared by low temperature solution method,a facile organic solvent method was used to synthesize NiO_x nanocrystals with less hydroxyl functional groups and H₂O molecules which degrade perovskite,and the nanocrystals can be stably dispersed in various solvents.Moreover,the NiO_xthin films with high transmittance,good electrical conductivity,strong hole extraction ability,and good energy level matching with the perovskite layer were prepared by a low temperature spin coating technique.An inverted planar perovskite device with NiO_x as the hole transport material exhibited a PCE of 18.49%and 15.94%on a rigid and flexible substrate,respectively.More importantly,the NiO_x-based devices retained 90%of their initial performance at 500 hours in a damp-heat test（85°C and 85%relative humidity）.（4）To avoid the disadvantage of low device stability caused by the use of organic charge transport layers,the PSCs with all-metal oxide charge transport layer has been successfully assembled by using the above-mentioned TiO₂ electron transport layer preparation process and high stability NiO_x nanocrystals.And a PCE of 12.35%could be achieved.Compared with the stability of the device based on organic hole transport layer,the all-metal oxide device shows obvious advantages in improving stability,which points out a new sight for constructing highly efficient and stable perovskite solar cells...