New Fullerene Derivatives Electron Transport Layer And Interfacce Modification Layer For Perovskite Solar Cells

Organic-inorganic hybrid perovskite solar cells(PSCs)have shown great potential in the field of photovoltaic power generation and rapid development in photovoltaic performance.The highest efficiency of PSC has reached 23.7%,surpassing the top efficiency of CdTe and CIGS solar cells in just about a decade,which is close to the efficiency of monocrystalline silicon solar cells.Perovskite light-absorbing materials can be prepared by simple and inexpensive solution processes,which demonstrate the immense potential of this thin-film solar cell technology to become a low-cost alternative to the commercially available photovoltaic technologies.Although PSCs have the potential for commercialization,several key issues must be addressed for the true industrialization of PSCs,including the preparation of large-area PSC devices,device stability,hysteresis,and the preparation of flexible devices.At present,the one-step preparation process can produce a high-quality perovskite film,but this process shows poor repeatability and is not suitable for large-area PSC devices fabrication.Among the most high-efficiency perovskite solar cells,TiO2 is still the most commonly used electron transport layer.However,the preparation of TiO2 requires high-temperature sintering process,which not only increases the preparation cost and makes the process complicated,but also limits its application on flexible substrates.Besides,the low electron mobility of TiO2 and its instability under ultraviolet light can cause serious hysteresis and poor stability of the fabricated device.In order to solve the drawbacks of TiO2,novel fullerene derivatives were used as electron transport layer and interface modification layer for PSCs.The main contents of this thesis are as follows:(1)A novel pyridine-functionalized fullerene derivative[6,6]-(4-pyridinyl)-C61-ethyl acid ethyl ester(PyCEE)was synthesized and applied as electron transport layer(ETL)to replace TiO2 in regular n-i-p perovskite solar cells.The PyCEE-based devices achieved champion power conversion efficiency(PCE)of 18.27%with significantly suppressed hysteresis,which is superior to that of TiO2-based devices.PyCEE has suitable energy levels and high electron mobility,which facilitates electron extraction and transport.Besides,the pyridine moiety within PyCEE affords coordination interactions with Pb2+ ion within CH3NH3PbI3,passivating the trap states of perovskite layer and jointly contributing to the improved PCE and dramatically suppressed hysteresis.Moreover,the use of the low-temperature solution-processed PyCEE ETL enabled fabrication of an efficient,flexible solar cell with a PCE of 15.25%,demonstrating its applicability in flexible devices and providing new opportunity for large-scale production and commercialization of perovskite solar cells.(2)New carboxyl-functionalized fullerene derivatives(CEBA,CEPA)were synthesized and used as interface modification materials between TiO2 and perovskite layers in PSCs.It was found that the surface of TiO2 modified by the fullerene derivatives was significantly improved,and the roughness was decreased.As a result,the crystallinity and the quality of the perovskite film grown on modified TiO2 surface were improved.At the same time,the electron mobility of the modified TiO2 film is also greatly enhanced.Moreover,the carboxyl group of CEBA or CEPA has a certain coordination effect with Pb2+ within CH3NH3PbI3,passivating the trap states of perovskite layer.As a result,hysteresis of the CEBA/CEPA-based devices has been obviously suppressed and the device performance was also improved in the same time.Our research provides useful guidance for the design and synthesis of novel fullerene interface modification materials for perovskite solar cells.