The Research On The Key Materials For Stable Perovskite Solar Cells

Perovskite solar cells（PSCs）have got substantial attention as the next-generation commercial photovoltaic materials due to their simple structure,low fabrication cost and outstanding power conversion efficiency.In recent years,the development of the PSCs is very rapid,the power conversion efficiency（PCE）of PSCs have reached22.1%.However,due to the materials of the PSC and low stability of the perovskite solar cells,it is still not commercialized.Therefore,it is very important to improve the stability of perovskite solar cell devices with high power conversion efficiency.Traditional attempts had been made to improve the stability of perovskite solar cells,such as modification of the perovskite sensitizer as well as the application of dopant-free or additives-free hole-transporting materials.The two methods have been considered as one of the simple and effective ways to improve the power conversion efficiency and stability of perovskite solar cells.Therefore,this paper starts from the key material that affects the stability of perovskite solar cells:perovskite active layer and hole-transporting layer,as a result,the photovoltaic performance and stability of the PSCs had been greatly improved.The perovskite active layer was prepared by one-step anti-solvent method,Pb I₂and CH₃NH₃I were mixed in a molar ratio of 1:1,the mixture of DMF/DMSO were used as the solvent,and chlorobenzene was used as the anti-solvent to obtain uniform and dense perovskite film.The crystal size of the perovskite is about 300 nm.The perovskite solar cells based on the structure FTO/Ti O₂/CH₃NH₃Pb I₃/HTM/Au can achieve the power conversion efficiency 17.51%.The cells show the good reproducibility with the average conversion of 16.83%.2-pyridylthiourea was used as the additive in the fabrication of the PSCs to tune the crystal-growth of perovskite thin films.As a result,with the introduction of 2-pyridylthiourea,the larger crystal grains with smaller pinholes can be obtained,along with the increase of the surface coverage.The separation and transport of the charge carriers in the perovskite can be improved by passivating the interface at the grain boundaries.Compared to the control device,the PCE of devices with 2-pyridylthiourea additive is obviously improved from 15.5%to 18.2%.Moreover,the devices with 2-pyridylthiourea show relatively better stability compared to reference devices when aged under ambient air of 55±5%relative humidity in the dark and under 65 ^oC after30 days.The PCE dropped to about 91%and 93%of the original,respectively.The polymer material PVB as an additive of anti-solvent chlorobenzene was applied to one-step anti-solvent method to promote crystal growth process of perovskite.The results show that the introduction of PVB can increase the perovskite grain size to obtain the perovskite film with high quality,along with reducing the amount and defect of grain boundaries.The photovoltaic properties can be improved by reducing the recombination of electrons and holes.Compared to the control device,the PCE of devices with PVB is obviously improved from 15.02%to 17.2%.Moreover,the devices with PVB show relatively better stability compared to reference devices when aged under ambient air of 55±5%relative humidity in the dark and under 65 ^oC after30 days.The PCE dropped to about 87%and 89%of the original,respectively.A novel hole-transporting material XY1 with TPB as the core was synthesized through Witting reaction.The structure was characterized by MS and NMR.The HOMO energy level of XY1 can be confirm to be-5.28 e V,which match well with the valence band of MAPb I₃ and the work function of gold electrode.The hole mobility is7.7×10^-5 cm² V^-1 s^-1.The perovskite solar cells with the non-doped hole-transporting material can achieve the power conversion efficiency of 12.87%,the perovskite solar cells based on XY1 show excellent stability.The power conversion efficiency of the cells based on XY1 can remain almost constant after 600 h by storing the unsealed devices in the room temperature with air humidity of 40%,indicating that XY1 has a promising stability than spiro-OMe TAD.