Solvent Engineering In High Efficiency Perovskite Solar Cells And The Device Research

Organic-inorganic perovskite solar cells(PSCs)have achieved great prograss during the past few years,and the power conversion efficiency has improved a lot in a short period of time.To date,the highest certified efficiency has excess 20%and has attracted even more attention around the world.However,there still exists problems that hinder the development of PSCs.For example,the MAPb I₃ perovskite films will not crystalized completely immediately after the deposition,they need thermal annealing.There exist hysteresis phenomenon during the current to voltage measurement.Besides,most researches are focusing on achieving high efficiency perovskite solar cells and investigations on the device encapsulating and the stability are very rare.In this dissertation,we firstly demonstrated a new instant-crystallization technique for deposition of perovskite films without the need for thermal annealing.The use of ethyl acetate(EA)induced instant and complete perovskite films crystallization at room temperature.This solvent engineering method could get instant crystallization of perovskite films without the need for thermal annealing.EA-perovskite films showed a larger crystal grain size,a longer photoluminescence lifetime,and low charge carrier recombination.We prepared PSCs with annealing and annealing-free EA-and toluene-perovskite films and evaluated the performance of the PSCs.The device based on the EA-perovskite film showed superior efficiency.Moreover,PSCs fabricated with annealing-free EA-perovskite films showed a high power conversion efficiency of 15.58%.The PSC based on the annealing-free EA-perovskite film exhibited high cell performance comparable to that of a PSC based on an annealed film;the power conversion efficiency of the former was 92%of that of the latter.This new instant-crystallization technique offers a way to shorten device-fabrication time,which will reduce the cost of manufacturing efficient PSCs.From the perspective of global photovoltaic commercialization,this instant-crystallization approach to deposition of annealing-free perovskite film can facilitate the fabrication of efficient and low-cost photovoltaics.We had a deeper insight into PSCs devices,and proposed a fast,effective and accurate evaluation strategy for PSCs with smallest hysteresis by facile controllable of the measurement parameters.We investigate the IV measurements hysteresis by changing the applied voltage step and the delay time,and observed that reducing the voltage step when measure the PSCs can effectively decrease IV measurement hysteresis compared to increasing the measurement delay time.A recommendation for how to measure highly effective and accurate IV characteristics for PSCs was given based on the above observations,which is beneficial for accurate evaluation of PSCs.We believe this measurement strategy will be of great useful in achieving precise and credible PSCs data.We further studied the encapsulation of PSCs.We studied two encapsulation process for large-are PSCs:thermal encapsulation and UV encapsulation,and improved the encapsulating process.We compared photovoltaic performance of the encapsulation and un-encapsulated devices,and got the influence rule of store time on PSCs.We investigated the store environment and atmosphere and found the UV encapsulation can effectively protect PSCs in a long time and ensure device stability in the open air.Based on the above investigations,we conclude that:the use of EA in solvent engineering method could get instant and complete crystallization of perovskite films without the need for thermal annealing and high efficiency PSCs.We could get accurate IV characteristics for PSCs by applying a smaller voltage step.Lastly,the UV encapsulation can effectively protect PSCs.We believe the above investigations on high efficiency PSCs could promote the commercial development of PSCs.