Investigation On Scaffold Layer Of Carbon-based Perovskite Solar Cell

In modern society,the global energy crisis is growing due to the increasing demand for energy.It is imminent to study and develop new energy to solve the shortage of fossil energy.Solar energy is known as one of the most promising options because of the green environmental protection,rich reserves and low cost.Compared with traditional silicon-based solar cells,perovskite solar cells?PSCs?with high efficiency,low cost,simple preparation and advantage of flexible devices are attracting researchers.In particular,carbon-based PSCs without hole transport material?HTM?are advantageous for large-scale production and application due to their low cost,high efficiency and stability.Electron transport layer?ETL?and mesoporous insulating layer as scaffold are the main component of PSCs.It plays an important role in photoelectric conversion efficiency?PCE?and stability of devices.In this paper,the effect of different mesoporous insulating layers on permeability and crystallinity of perovskite is studied.The PCE of device is improved by increasing the crystallinity of perovskite and the formation of large grains.The effect of electron transport material morphology and ETL thickness on the performance of PSCs is also discussed.Moreover,reasonable electron transport paths were proposed to investigate the charge recombination mechanism in PSCs.Fast electron transfer and low charge recombination at interface improve PCE of devices.The work in our paper as follows:?1?TiO₂ nanosheets were prepared by hydrothermal method using tetrabutyl titanate?TBT?as titanium source.Then TiO₂ slurry can be obtained to prepare TiO₂ETL by screen printing technology.In the same way,Al₂O₃ or ZrO₂ paste were also prepared to print an insulating mesoporous layer.The prepared carbon paste was printed on the top of Al₂O₃ or ZrO₂ insulating mesoporous layer.After calcination,the perovskite precursor solution was dropped onto the surface of mesoporous carbon layer to obtain the entire device.It was found that PSCs based on mesoporous ZrO₂insulating layer obtain the short-circuit current density(J_sc)of 20.2 mA cm^–2 and PCE of 8.72%,which are 23.17%and 59.12%higher than that of PSCs based on mesoporous Al2O3 insulating layer,respectively.The results show that the larger particle size in ZrO₂ insulating layer results in the relatively smaller specific surface area and the larger pores.These larger voids are favorable for the infiltration and crystallization of perovskite precursor solution,generating large grains to reduce the crystal boundaries.Hence,the higher photocurrent and energy conversion efficiency will be achieved.?2?The single crystal anatase phase TiO₂ nanosheets?NSs?were synthesized by hydrothermal method by using tetrabutyl titanate?TBT?,hydrofluoric acid?HF?and deionized water as raw materials.The obtained anatase phase TiO₂ NSs has the length of 97 nm and the thickness of 13 nm.Then,the different concentrations of TiO₂pastes were prepared by TiO₂ NSs,which are acted as electron transport materials.Effect of TiO₂ NS layer thickness on the photo-generated electron transfer,charge recombination at interface and PCE of PSCs is studied.After optimization,perovskite solar cell with 1.0?m TiO₂ NS layer shows a superior efficiency of 8.11%.It is proposed that the?001?facet of TiO₂ NS is highly active,which will enhance the attachment of CH₃NH₃PbI₃ to the TiO₂ NS surface.It will facilitate the injection of electrons from CH₃NH₃PbI₃ into the TiO₂ NSs.The thicker TiO₂ NS layer will has the lower charge recombination at the interfaces because of the larger recombination resistance,which improves the performance of PSCs.