Study On Interface And Working Mechanism Of High-efficiency And Stable Perovskite Solar Cell Devices

Solar energy is an economic and clean renewable energy source with the great development potential.Making full use of the solar energy can alleviate the environmental pollution and energy crisis caused by fossil energy.The organic/inorganic halide perovskite material is a crystal material self-assembled by hydrogen bonding of an organic component and an inorganic framework,which has the advantages of both organic and inorganic component materials.The organic/inorganic halide perovskite exhibits excellent performances in the fields of optics,electricity,and magnetism,and has bcome a research hotspot in the field of photovoltaics currently.The photovoltaic conversion efficiency?PCE?of photovoltaic devices with the organic/inorganic halide perovskite active layer can be up to²3.7%,comparable to crystalline silicon cells.The efficient interface charge transfer process and high quality perovskite film are crucial for the fabrication of high-efficiency devices.However,beyond the improvement of the efficiency,the long-term stability under moisture and continuous illumination is still remains a challenge for commercial application.To address the above issues,this thesis is therefore mainly focused on the optimization of the transport layer material,the interface modification of organic/inorganic halide perovskite devices as well as the utilization of two-dimensional perovskite.With various techniques including transient absorption,transient photocurrent/photovoltage,electrochemical impedance spectroscopy and multi-light intensity experiment,the charge transfer,recombination process and performance of PSC are studied systermatically,aiming to achieve a high efficiency,stable,and reproducible devices and clarify the charge transport mechanism of PSC interface,and thus promote the commercialization of PSC.Firstly,to improve the hole transporting capacity of the mesoporous structure?TiO₂/Al₂O₃/C?,the single-walled carbon nanotube?SWCNTs?was used to prepare a novel SWCNTs-doped graphite/carbon black counter electrode?CE?.Device with this kind of CE has a more smooth energy level align due to the improved work function of the counter electrode accompany with a faster hole transport process,the final device efficiency reaches 14.7%.Secondly,we utilizes the carbon quantum dot/TiO₂ composite material as the transport layer in the planar n-i-p structure device,this new transport layer shows high transmittance,uniform and smooth surface,high electron mobility and well-matched energy levers,finally a device efficiencies up to¹9%was achieved.Thirdly,due to the surface defects of perovskite materials,we synthesized functionalized reduced graphene oxide?rGO-4FPH?material as interface modification layer.The density functional theory?DFT?calculations and other experiments proved that rGO-4FPH passivate the surface defects of lead vacancy,the device open circuit voltage and PCE are greatly improved.Throough the above-mentioned transport layer material optimization and interface modification,high-efficiency PSC devices have been successfully fabricated.The faster interface transport process and relatively lower surface defect state are the key to preparing high-efficiency devices.At the same time,these provides a feasible idea for the application of new materials in perovskite devices.To develop the stability,the application of two-dimensional?2D?perovskite materials in devices is explored.It's well known that the 2D perovskite has the superior stability,but suffered low device efficiency.The 2D perovskite material growth is a critical issue for the preparing of high-efficiency devices.Firstly,the cation-induced crystallization method was used to form a highly uniform orientation characteristic 2D perovskite,and the defect state caused by uneven crystal growth is also suppressed.Combined with TiO₂/Al₂O₃/NiO/C mesoporous devices,the device achieves a stability of up to 4000h.Our work make the PSC more stable and efficiency for further commercialization.Another problem that needs to be addressed which limits the photovoltaic efficiency of 2D material devices is the excessive exciton binding energy and lower charge mobility problems caused by quantum and dielectric confinement effects.In response to this critical problem,we fabricated lithium-ion?Li⁺?-doped 2D perovskite materials to fabricate a device based on the planar p-i-n structure,achieving a device efficiency of¹5%.DFT calculations show that the difference in dielectric constant between the organic spacer cations and the inorganic framework is reduced,there by reducing the Coulomb force effect between electron-hole pairs and the dielectric confinement effect inside the film.The reduction of exciton binding energy was confirmed by the fitting of the temperature dependent steady-state fluorescence,and the charge mobility was also improved.This work highlights the promising ionic doping engineering for further improvement of the layered perovskite materials.