Study On Defect Passivation Of The Light-absorbing Layer And Performance Of Carbon-based Perovskite Solar Cells

Recently,the certification power conversion efficiency(PCE)of the state of art perovskite solar cells(PSCs)has already been raised up to 25.5%,approaching the commercial monocrystalline silicon solar cell,which arouses widespread attention in the world.However,the structures of most high-efficiency PSCs are still adopting traditional planar heterojunction structure with expensive organic hole-transport materials(HTM)and metal counter electrodes.As we all known,high-price organic HTM shows strong hygroscopicity and precious metal counter electrode evaporated by energy-consuming thermal evaporation in vacuum not only increase the cost but also adversely affect the device stability.Fortunately,HTM-free Carbon-based PSCs(C-PSCs)have been reported to be an alternative owing to ambipolar property of perovskite and similar work function of carbon to Au(～5.0 eV).But there still remains two serious problems:Firstly,poor-matched energy level between perovskite and low-work-function carbon electrode restricts the improvement of the corresponding open-circuit voltage(VOC)and efficiency.Secondly,the rapid crystallization of perovskite prepared at high temperatures,which is commonly used,will directly lead to a variety of undesirable defects in grain boundaries and interior.The resulting trap-assisted non-radiative recombination centers will hinder charge transfer,further destroy the performance and stability of the devices.Therefore,it is imperative to simultaneously improve both efficiency and stability of PSCs by passivating the defects of light-absorbing layer and optimizing the energy levels of carbon electrode.In this thesis,the hole-free transport-layer PSCs based on carbon electrode are fabricated,which are dedicated to passivate the defects of perovskite,so as to modulate the quality of the perovskite film,enhance the photoelectric performance,and also reduce the hysteresis effect of the device.Besides,the inorganic hole transport materials CuPc are added into the carbon layer as to assist efficient extraction and transmission of holes.The specific research is as follows:(1)A defect-healing method based on treatment of MAPbI3 film using phenethylammonium iodide(PEAI)as surface passivator and coating highly conductive CuPc on carbon(CuPc-C)paste was combined to improve the photoelectric conversion efficiency of PSCs with the structure of FTO/c-TiO2/m-TiO2/MAPbI3/PEAI/CuPc-C,Firstly,the effect of the different concentrations of isopropanol solution of PEAI on the MAPbI3 perovskite membrane was investigated.It was found that the PEAI treatment effectively passivates the perovskite surface and simultaneously lowers the surface roughness.PEAI behaves as a hydrophobic organic capping layer to avoid the moisture invasion pathway and compensate for the lower absorption and charge-carrier transport interruption of low-dimensional materials,which in turn markedly suppresses surface charge recombination and enhance the contact of perovskite with carbon electrode.Additionally,a more cheap and simple approach was merged to overcome the issues of insufficient hole extraction and the poor transfer dynamics,by mixing CuPc directly into the paintable carbon paste to form an accessible Schottky junction at the MAPbI3/Carbon interface.The VOC and fill factor(FF)of the device were also improved.The experimental results show that the PSCs treated with 10 mM PEAI on MAPbI3 film and 1.0 wt%CuPc modified carbon electrode exhibit the best performance.The overall device acquire the champion PCE of 13.41%,which constitutes an～21.9%enhancement compared with that of the control device and 14%over that of the PEAI-passivated device.It also exhibits excellent moisture tolerance and stable stability.Especially,the current density-voltage(J-V)response curve of the device shows minimal hysteresis effect to some extent.(2)A high-cry stall inity inorganic CsPbBr3 film was fabricated by a modified multistep spin-coating technique,and then was post treated by phenyltrimethylammonium chloride(PTACl)/Isopropanol solution,achieving the bi-functional stabilization by chloride ion(Cl-)doping and PTA+ cation surface passivation.As expected,all-inorganic PSCs with the constructure of FTO/c-TiO2/m-TiO2/CsPbBr3/PTACl/CuPc-C are high stability and photoelectric efficiency is improved.Furthermore,the mode of PTACl post-treatment,including spin coating and soaking was investigated.In addition,the effect of PTACl concentration of isopropanol solution on the performance of CsPbBr3 was explored.It was observed that the grain size of perovskite did not change basically and the surface morphology was relatively smoother after 1mg/mL PTACl/Isopropanol spin-coating treatment.The Cl-doped into CsPbBr3 perovskite lattice lead to the contraction of the lattice and improved crystallinity,while the hydrophobic organic cation PTA+ can passivate the surface,thus reducing the defect state density as well as improving the moisture resistance of the CsPbBr3 film.In conclusion,the photoelectric properties of CsPbBr3 films can be improved by spin-coating and short-time soaking,but soaking treatment can not be well controlled.It was also found that the crystal structure was destroyed when soaked over 30 min.Besides,the light absorption performance of all inorganic PSCs devices spin-coated with 1 mg/mL PTACl was significantly enhanced,corresponding to a better current density(Jsc),the VOC and FF,even the photoelectric conversion efficiency was increased from 5.76%to 6.38%with long-term stability.