The Absorber Layer Preparation And Interface Modulation For Efficient And Stable Perovskite Solar Cells

The perovskite solar cell is one of the most promising next-generation photovoltaic devices,in which has the advantages in high efficiency,low cost and easy processing.However,the abominable current density-voltage hysteresis-and bad long-term stability are lagging behind its application and commercialization.Thus,suppressing the hysteresis and improving device stability are most important problems to be solved.The aim of this thesis focuses on preparing high efficient and stable perovskite solar cells.Firstly,the high-quality perovskite absorber layer with high absorption and crystallization were prepared in the two-step method,and the additive were introduced in the perovskite precursor to further improve the perovskite layer morphology and crystalline properties.Then,element doping were employed to modulate the energy level alignment between the perovskite layer and electron transfer layer to improve carrier transfer and suppress hysteresis behavior.On this basis,the hydrophobic layer was inserted between the perovskite layer and hole transfer layer to improve the device stability.The detailed descriptions are summarized briefly as follows:1.In the two-step method.the anti-solvent(chlorobenzene)treatment induces the compact PhI2 layer to mesoporous structure.The absorption spectroscopy and x-ray diffraction measurements were employed to investigate the effects of different PbI2 morphology on the perovskite phase transformation.The anti-solvent treatment leads to compact,uniform and pinhole-free perovskite films,and improve the perovskite absorption and crystallization significantly.This results from that the anti-solvent treatment generates amount of voids in the whole PbI2 film,which are beneficial for effective penetration of the methylammonium halide solution into the deep PbI2 layer.By fabricating the solar cell using this anti-solvent treatment,the device per-formance increased from 12.05%to 16.09%(the best PCE of 17.11%)with less hysteresis.And the PCE of the perovskite solar cell with treatment remains over 90%of the initial PCE after 30 days in ambient air stored in the dark.2.For further improving the perovskite crystalline properties,the lead acetate additive is introduced into the stoichiometric lewis acid-base perovskite precursor.By combining the SEM images and x-ray diffraction measurements,the perovskite grain size grows from 206 nm to 291 nm,and the perovskite crystallization improves strikingly.With steady-state and time-resolved photoluminescence spectroscopy measurements,it can be found that the non-radiative recombination decreases and the carrier lifetime increases,which is related to defect or trap passivation by the PbI2 byproduct at the grain boundary.The fabricated perovskite solar cells with lead acetate can achieve an average power conversion efficiency of about 18.06%(the best efficiency of 18.86%)with a stabilized power output of 18.28%.3.The Yttrium element was successfully doped in the TiO2 electron transfer layer by adding the YCl3 into the compact TiO2 precursor,and the influences on the transmittance,conductivity and energy level distribution were investigated systematically.It can be found that the Y doping enhances the film transmittance and conductivity,and induces an upward shift of the bottom position of conduction band in the TiO2 layer.This results in decreased charge accumulation and weak interface capacitance,which is better for suppressing hysteresis.With the optimized YCl3 concentration,the perovskite solar cells achieve a best power conversion efficiency(PCE)of about 19.99%(19.29%at forward scan)and with a steady-state power output of about 19.6%.4.The hydrophobic polystyrene layer was introduced between the perovskite layer and hole transfer layer.By analyzing the steady-state and time-resolved photoluminescence spectroscopy measurements,the polystyrene layer can significantly passivate the traps and defects at the interface of perovskite film and spiro-OMeTAD layer nd decrease the non-radiative recombination.which is responsible for the enhanced photoluminescence intensity and carrier lifetime.With polystyrene layer,the perovskite contact angle increases from 75.1° to 92.5° to impede the moisture penetration into the perovskite absorber layer.The fabricated perovskite solar cells with the polystyrene layer achieve an enhanced average power conversion efficiency of 19.61%(20.46%of the best efficiency)from 17.63%,and with a negligible hysteresis.Moreover,the optimized perovskite solar cells with the hydrophobic polystyrene layer,can maintain about 85%initial efficiency after two months storage in open air conditions without encapsulation.