Structure-Related Performance In Hybrid Solar Cells Of Planar Heterojunctions Based On TiO₂ Polycrystalline Films

Due to its nontoxicity,stability to environment,transparency to visible light,high electron mobility and ease availability at low temperature,TiO2 nanostructured film has been a commomly used electron acceptor and transport layer in solar cells.In this dissertation,with the hybrid perovskite and Sb2S3 as light-absorber,we mainly investigate the solution-processed in-situ growth of bulk light-absorber layers on TiO2 nanostructured films and the device performance in the related solar cells.The main contents and conclusions are as follows:(1)Preparation of CH3NH3PbI3 bulk layer on TiO2 film and structure-correlated device performance in its solar cell.We prepare the high-quality CH3NH3PbI3 bulk thin film by the two-step method at a low temperature(<80 ?),and investigate the effects of PbI2 crystallization on the formation of CH3NH3PbI3 thin film and the correlation between CH3NH3PbI3 film structure and solar cell performance.Results show that a better crystallized PbI2 film produces larger CH3NH3PbI3 grains with a higher crystallinity and a better performance and stability in the solar cells.It is found that the importance of the crystallization in PbI2 matrix lies in governing the transition from the(001)plane of trigonal PbI2 to the(002)plane of tetragonal CH3NH3PbI3 during spin-coating,which governs the morphology and the defect types in the final CH3NH3PbI3 film;the significantly improved photocurrent and higher open-circuit voltage in the solar cells derived from a better crystallized PbI2 film are,respectively,due to the increased hole mobility and the reduced vacancy defect density as the results of the higher crystallinity inside perovskite film?(2)Preparation of Sb2S3 bulk layer on TiO2 film and its solar cell.The monolayer of randomly orientated and closely packed Sb2S3cuboids is grown in-situ over the TiO2 polycrystalline film in a large area by a solution-processing method,offering a Sb2S3/TiO2 planar heterojunction.After studying the growth features of the Sb2S3 cuboids,an orientation-competing-epitaxial nucleation/growth mechanism is proposed for the in-situ growth of bulk single-crystals on polycrystalline surface.A novel and stable solar cell based on the Sb2S3/TiO2 plannar heterojunction is fabricated using an organic composite hole transporting layer,yielding the devices with a broad absorption in 300-900 nm nm and a best power conversion efficiency of 4.39%under standard test conditions(AM 1.5G,100 mW/cm2);for such solar cell,the principled functions of the materials are elucidated and it is revealed that the open-circuit voltage origin is determined by the quasi-Fermi levels of electrons in TiO2 and the holes in Sb2S3.