Study On Morphology And Crystallization Control For Enhancing Device Performances Of Solution-Processed Perovskite Solar Cells

Solar cells based on mixed organic-inorganic halide perovskites are promising photovoltaic technologies with low-cost and fantastic photoelectric power conversion efficiency?PCE?.Since perovskite semiconductors were incorporated into photovoltaic devices in 2009,the PCE above 22% have already been reported and authenticated in only a few years.A key to this success is the development of various solution-synthesis and film-deposition techniques for controlling the morphology and composition of hybrid perovskites.Hence,at present study of perovskite solar cells?PSCs?have been focused on solvent engineering,interfacial engineering and optimizing morphology and crystallinity of perovskite layer.In this thesis,we focused on the performance improvement of planar heterojunction?PHJ?PSCs via controlling morphology and regulating the nucleation and crystallization of perovskite crystals,and carried out the following works:?1?Pure chlorobenzene?CBZ?and 2-propanol?IPA?or mixed-solvent assisted spin-coating have been applied to one-step fabricate CH₃NH₃PbI₃ and CH₃NH₃PbI_3-xCl_x perovskite films,respectively.However,with the treatment of pure-or mixed solvent,there are obvious differences in the formation of CH₃NH₃PbI₃ and CH₃NH₃PbI_<sub>3-xCl_x perovskite films with full coverage and large crystal grain size,as well as the role in the photovoltaic performance.Furthermore,the nucleation and growth dynamics of perovskite crystals have been taken into consideration with the activation energy of transporting crystallizing segments across the crystal interface and the formation free energy of a critical-sized nucleus.PHJ PSCs based on CH₃NH₃PbI₃ by mixed-solvent treatment exhibit a poor PCE owing to the formation little amount of perovskite crystals with low crystallinity.While pure CBZ treatment renders the corresponding device get efficiency of 8.1%,which is due to the formation of uniform CH₃NH₃PbI₃ thin film with higher surface coverage and crystallinity.Inversely,PSCs based on CH₃NH₃PbI_3-xCl_x with mixed-solvent shows the highest PCE of 9.2%,shortcircuit current density?Jsc?of 16.06 m A/cm² and fill factor?FF?of 63.6% with high device reproducibility and low photocurrent hysteresis,by reason of possessing higher light absorption ascribed from bigger crystal size and better surface morphology with no pin-holes.These results will provide significant guidance for CH₃NH₃PbI₃ and CH₃NH₃PbI_3-xCl_x perovskite device performance optimization and large-scale application by pure-and mixed-solvent treatment.?2?Enhancing nucleation and regulating crystallization rate of the perovskite films are crucial to the photovoltaic performance of PSCs.Here,we introduce a simple approach to fabricate perovskite films with full coverage and larger crystalline size by incorporating polyurethane?PU?into the perovskite precursor solution to control nucleation and retard the crystallization rate.We obtain shiny smooth perovskite films with compact micron-sized crystalline grain,which exhibit excellent photoelectric performance.Furthermore,the PU additive can balance and stable the uniform distribution of charge in perovskite,and inhibit iodine ion migration.The PSCs fabricated by PU incorporating in the perovskite precursor offer an impressive PCE of 18.7% with almost no photocurrent hysteresis and excellent stability in ambient air.