Investigation Of The Perovskite Solar Cells Based On The Light Conversion And Structure Optimization

With the raipd development of the society and technology,the energy is consumed more and more by humans,and the energy demand is also growing.Therefore,it is urgent to seek renewable and environmentally friend and clean energy.The solar energy as the most abundant clean energy in the world,it is fully capable to satisfy the growing energy demand of the world.Hence,the solar cells based on photovoltaic effect have become a hotspot in this field.The power conversion efficiency?PCE?of solar cells based on the organic-inorganic hybrid perovskite materials have been improved from 3.8%to more than 23%in recent years,which is able to compete with the conmerical silicon-bansed soalr cells.The excellent performance of perovskite solar cells?PSCs?make them as the promising photovoltaic devices of next generation.Although the prospect of the PSCs is promising,but the stability of the PSCs still represents a major obstacle that must be overcome before practical applications of PSCs.Therefore,we mainly studied the stability of the PSCs in this work.The main results are:?1?TiO₂ is usually used as electron transfer material in PSCs.However,if TiO₂ is exposed to ultraviolet?UV?light for a long time,the oxygen vacancies at the surface of TiO₂ can react with I^-ions in CH₃NH₃Pb I₃,resulting in the degradation of of CH₃NH₃PbI₃ and decreased the device performance.As a new member of the carbon nanomateral family,fluorescent carbon dots?CDs?have good absorption in UV region,tunable optical and electronic properties.We introduced the CDs into the mesoporous TiO₂?m-TiO₂?,which could effectively convert the UV light into blue light and to be utilized by the perovskite layer.Using this effective approach,we observe that both stability and PCE can be considerably improved.Accordingly,PSCs with CDs can maintain nearly 70%of initial efficiency after 12 h full sunlight illumination compared to the devices without CDs?20%?,meanwhile the PCE improves from 14.6%to 16.4%as CDs are incorporated into PSCs.Our results indicate that incorporating an ideal luminescent down-shifting?LDS?material into PSCs would be a promising approach to enhance the photovoltaic performance and the UV light stability of the devices.?2?Beside the CDs,some rare earth doped phospohrs,such as YVO₄:Eu³⁺,Bi³⁺LDS material also has a high absorption coefficient in the 220-350 nm UV range.It can convert the UV light to an intense red light and to be utilized by the perovskite layer.We incorporated the YVO₄:Eu³⁺,Bi³⁺into the mesoporous TiO₂,which can suppressed effectively the damage of the perovskite film and enhanced the utilization of the sunlight.By controlling the YVO₄:Eu³⁺,Bi³⁺concentrations,an optimized PCE of 17.9%is obtained,which has an improvement of 9.8%compared to that of the control device.In addition,the device based on m-TiO₂/YVO₄:Eu³⁺,Bi³⁺layer has excellent stability under UV light irradiation,which can still maintain70%of the initial efficiency after 60 h UV irradiation.?3?The quality of perovskite layer is very critical to achieve high device performance.Here,we introduced the ZnCl₂ into the precursor solution of perovskite to improve the quality of perovskite film and explored its effects on perovskite morphological,optical properties,and the performance.By controlling the ZnCl₂ concentrations,we achieved a good perovskite film with large grain size and better morphology.Consequently,the device with ZnCl₂ shows greatly improvement in PCE from 16.4%to 18.2%compared to control device.More importantly,the device is more stable than the control device,with only 7%degradation after aging 30 days.These results are attributed to the increased grain size,improved film morphology and reduced recombination loss after the partial substitution of PbI₂ by ZnCl₂ in perovskite film.This work develops a new approach for morphology control through rational additives in the perovskite film,and paves the way toward further enhancing the device performances of PSCs including PCE and stability.?4?Ce-doped TiO2 was prepared through the e-beam evaporation method is examined the electron transport layer?ETL?for perovskite solar cell.In light of the existence of Ce ion,the transport ability of electron from perovskite layer to ETL is improving.Therefore,the corresponding PCE is increased form 17.98%to 19.36%.Furthermore,in order to improve the light stability of the device,the perovskite quantum dots?PQDs?were coated on the incident light of the device.Because of the PQDs have a high absorption in the UV region and convert the UV light to an intense green light through the luminescent down-shifting.By controlling the coated times,an optimized PCE of 20.02%is obtained and the device is more stable under UV light irradiation than the control device,which can still maintain 80%of the initial efficiency after 100 h UV irradiation.In addition,we used the Al₂O₃ to encapsulate the device which greatly improved the long-term stability.The PCE of device decreased only 7%after aging 1000 h.