Formation Of Artificial Pores In TiO₂Mesoporous Layer For High-efficiency Perovskite Solar Cells

The perovskite solar cell based on organic–inorganic hybrid perovskite materials(CH3NH3PbX3,X=I,Br,Cl) has attracted widely attention for its high light absorptioncoefficient, high photoelectric conversion efficiency and low cost. It becomes a star ofhope in photovoltaic power generation, because of its satisfactory photoelectricconversion efficiency. Mesoporous perovskite solar cell is an efficient devicestructure. This study finds that the mesoporous layer plays a very important role inperovskite solar cells, it is not only the electron transport layer, but also the supportframe of perovskite material. Pores in the mesoporous layer can guide the growth ofthe perovskite grain, which affects the crystallinity and morphology of the perovskite.The purpose of this study is to increase the size and amount of pores which improvethe coverage and the grain size of perovskite. In this way the diffusion can beenhanced and the recombination can be reduced.Unique method of the present paper is to add carbon nano-tube, nano-graphite andacetylene black in the spin coating solution of TiO2mesoporous layer, and removethese carbon materials by high temperature sintering. Additional pores can beproduced in the electron transport layer, which result in improved photoelectricconversion efficiency for perovskite solar cell. The experimental results are as follows:1、 We have optimized the amount of carbon material, the thickness of themesoporous layer, and the hole transport materials by a series of experiments. We setthe amount of carbon material is10wt%of TiO2, the ratio of TiO2slurry to ethanol is1:3, and the hole transport material is OMeTAD. The results not only determine theoperation of core experiment, but also provide reference for related research.2、 Comparing the pore-formation of the three carbon material, we find theacetylene black is superior to the others. SEM image shows that the grain size andcoverage of the perovskite based on the four different mesoporous structure is quietdifferent. This indicates that the mesoporous structure greatly affects the crystallinity and morphology of the perovskite for the devices. Based on the four mesoporouslayers of no carbon materials, carbon nano-tube, nano-graphite and acetylene black,the lifetime of photocurrent decay is0.102ms,0.098ms,0.037ms and0.027ms, thelifetime of photovoltage decay is1.36ms,1.85ms,2.71ms and5.29ms, respectively.The results indicate that the diffusion of the carrier is enhanced, while therecombination of electron-hole decreased. Short circuit current density of the fourkinds of device is11.5mA/cm2,13.6mA/cm2,14.4mA/cm2and16.6mA/cm2,respectively. Photoelectric conversion efficiency increases from the initial7.91%to9.35%,9.98%and11.6%. The improvement is significant.This work shows the importance of the porous structure in the mesoporous layers,and also provides a method to control the porous structure, which can improve thecrystallinity and morphology of perovskite, and increase the photoelectric conversionefficiency of the device.