Research On Crystallization Kinetics Engineering To Improve The Efficiency Of Perovskite Solar Cells

Organic-inorganic hybrid perovskite as a light-absorbing material applied to photovoltaic devices has attracted widespread attention.The power conversion efficiency（PCE）of perovskite solar cells（PSCs）has increased from the initial 3.8%to 25.5%.However,its commercial application still faces many difficulties,such as the preparation of large-area perovskite films,the improvement of device stability（temperature and humidity stability）,and the improvement of the charge transport process.High crystallinity,low defectdensity of states perovskite film is the primary requirement of high-performance perovskite solar cells,and thecrystal growth kinetics regulation is one of the effective method to prepare perovskite films with high crystallinity and low density of trap states to improve the performance of PSCs.1.Functionalized carbon nanotubes facilitated perovskite crystallization.In this work,we used functionalized carbon nanotubes（f-CNTs）as an effective additive to improve the PCE of PSCs.We selected unfunctionalized carbon nanotubes（CNTs）and amino-functionalized carbon nanotubes（NH₂-CNTs）and carboxyl functionalized carbon nanotubes（COOH-CNTs）as additives.Although the PCE of PSCs with CNTs as additives（13.91%）is lower than that of original devices（16.56%）,the PCEs of PSCs with NH₂-CNTs and COOH-CNTs as additives are 17.47%and 17.75%,respectively.By optimizing the length and concentration of COOH-CNTs,the PCE of PSCs with short COOH-CNTs（2μm）as an additive was increased to 18.68%.Detailed studies have shown that COOH-CNTs as an additive can promote the crystallinity of the perovskite film.In addition,compared with the control sample,the hole mobility of the perovskite film with COOH-CNTs（2μm）as an additive increased by an order of magnitude,which is beneficial to the charge transfer in PSCs.At the same time,the stability of PSCs with COOH-CNTs（2μm）as an additive is also greatly enhanced.Our research provides a feasible strategy for the development of high-performance perovskite optoelectronic devices using functional one-dimensional carbon-based materials.2.Solvent engineering assisted perovskite crystallizationIn this work,we used solvent annealing to induce the secondary growth of MAPb Br₃perovskite crystals.Thermal annealing is performed in a solvent atmosphere of N,N-dimethylformamide（DMF）to obtain a perovskite light absorbing layer with uniform and compact crystal grains covering the substrate.The FF of PSCs has also been significantly improved.Compared with the 7.71%PCE of the control device,the PCE value of PSCs reached 8.84%after DMF solvent annealing.At the same time,because the film has better crystalline properties and reduced grain boundaries,it is not susceptible to corrosion and decomposition by water molecules in the air,and the stability of the device is also improved.