Research On Additives And Interface Layer Materials In Methylamine-formamidine-based Perovskite Solar Cells

At present,the laboratory certified energy conversion efficiency of perovskite solar cells has reached to 23.7%.In order to improve the performance of perovskite solar cells,we can improve the quality of perovskite absorbers and design or modify the interface transport layers.In this thesis,the performance of perovskite solar cells is improved using the high quality of perovskite absorbers with dopants and the excellent electron transport materials.At the same time,we also study the functional mechanism of additives and the recombination mechanism of carriers at the interface in perovskite solar cells.The main contents and results of the thesis are summarized as following.(1)Although the PbCl2 has been exploited to improve the performance of perovskite solar cells,the mechanism of enhancement by the introducing PbC12 is not fully understudied.We used the PbC12 as a dopant to improve the quality of perovskite film,we found the crystallinity and grain size of perovskite film both increased with 10%molar ratio of PbC12.The in situ time-resolved grazing incidence wide-angle X-ray scattering measurements revealed that more pre-nucleated suspended in the solution when employed the PbCl2 dopant,leading to high crystallinity of perovskite film.We uncover the function of PbC12 in reduced trap density,decreased charge recombination and enhanced carrier lifetime.As a result,the efficiency of planar-structure perovskite solar cells based on PbC12 enhanced to as high as 19.79%with reduced hysteresis,increased by?23%compared to the device without PbCl2(16.05%).(2)Conjugated polymer materials have been brought together with PCBM to form a bulk homojunc-film(BHJ),which possesses high electron mobility and suitable energy level.The BHJ film can completely cover the perovskite surface.More importantly,the BHJ film exhibits the larger permittivity compared to pristine PCBM,resulting in smaller electron capture region.We have employed the BHJ films as the electron transport layers(ETLs)to fabricate the inverted PSCs,the efficiency amazingly exceeds 20.6%with the record fill factor of 0.82,increased by about 20%compared to the control device with pristine PCBM.The stability of the devices is meaningfully improved due to the more hydrophobic ETLs.Under the ambient air condition in the dark for 45 days,the efficiency of inverted PSCs based on BHJ remains 80%of the initial value,which is increased by 16.6%than that of the control cells.(3)TiO2 doped with the metal Mg element is used as the ETL,which is fabricated by chemical bath deposition at low temperature.The experimental results reveal that the 1 mg/ml Mg-doped TiO2 film displays a good optical transparency property,leading to large photocurrent in perovskite solar cells.It is found that the ETL also has high electronic mobility and conductivity.These excellent properties would effectively suppress the electrons accumulation at the interface and passivate the electrons defect state density in perovskite film.As a result the devices with TiO2:Mg(1 mg/ml)ETLs exhibite the reduced hysteresis.The energy conversion efficiency of methylammonium-based(MAPbI3)perovskite solar cells reached to 18.02%,and the mixed methylammonium and formamidine-based(FA0.85MA0.15PbI3)perovskite solar cells is up to as high as 20.53%.