Efficient And Stable Perovskite Solar Cells Based On Carbon-Based Hole-Transport-Layer-Free Perovskite Solar Cells

In recent years,perovskite solar cells（PSCs）have attracted wide attention because of their low production cost,simple preparation method and great industrialization potential.Although the efficiency of PSCs has been improved to 25.8%,its stability is very poor,which seriously hinders its industrialization development.To solve this problem,previous researchers have developed hole-transport-layer-free perovskite solar cells with carbon electrodes with high stability.Although the devices have high stability,its efficiency is much lower than that of conventional devices.The main reason is that the hole extraction ability of the carbon electrode is poor,and the interface contact between the carbon electrode and the perovskite is also poor,which leads to serious charge recombination.Based on this problem,this paper starts with the charge recombination at the interface,and improves the performance of the device by reducing the charge recombination.The specific research work is as follows:（1）MAPbI₃ perovskite film was prepared by one-step method,and the pre-crystallized perovskite film was treated by hot pressing,and the influence of different hot-pressing temperatures on the film efficiency and charge recombination was deeply explored.In order to reduce the grain boundary density and improve the crystalline quality of the chalcogenide films,we have hot-pressed the pre-crystallised perovskite films,allowing the grains to grow in the direction of the horizontal under hot-pressing,obtaining large-sized grains and improving the crystallinity of the films.Through measurements,we found that the film with large grain size,smooth and compact without pinhole can be obtained by hot pressing treatment.We fabricated the hole-free carbon electrode PSCs by this method.Through J-V test,it was found that when the hot-press temperature is 80℃,the efficiency of 14.27%is realized,which was significantly improved compared with the device fabricated by the original method.The electrochemical test results also show that the fabricated thin films with fewer grain boundaries and larger grain size are helpful to reduce charge recombination in the device.（2）A solid-state heat-pressure method is proposed for the preparation of 2D/3D perovskite thin films with distinct layer sides,and the energy band of the thin films can be adjusted.We overlaid the pre-crystalline 2D perovskite film on the annealed 3D perovskite film,and grew a layer of 2D perovskite（Ph DMA）MA₃Pb₄I₁₃ on the 3D layer by heating and pressurizing it.By PL and TRPL measurements,we found that the 2D perovskite layer inhibited the non-radiative recombination and promoted the separation of electrons and holes.When exploring the growth mechanism of solid-state heat-pressure,we found that the pressure and heat had a great influence on the morphology of the 2D layer grown by solid-state heat-pressure.When the hot-pressing temperature was 60℃,we obtained the best quality of the carbon electrode PSCs device without holes,with an efficiency of 15.63%,which was higher than that of the device treated by hot pressing.This is because the typeⅡenergy band was formed and the hole extraction ability of the carbon electrode was improved.Moreover,the high stability and hydrophobicity of 2D perovskite improve the moisture resistance and long-term stability of the device.