Study Of High Performance Perovskite Solar Cells Based On Planar P-i-n Structure

Because of their unique electrical and optical properties,including tunable energy bandgap,high absorption and long carrier diffusion,perovskite solar cells?PSCs?have attracted much attention from they were invented from 2009.In the past few years,the power conversion efficiency?PCE?of PSCs has been promptly from initial 3.8%to the highest 22.1%certified by National Renewable Energy Laboratory?NREL?.Due to their low cost and simple preparation process,the technology of PSCs shows tremendous commercial potential.However,there are some problems for PSCs,such as poor stability,hysteresis effect,to be solved.In view of these problems,we focus on the carries transport properties,perovskite film formation kinetics and stability issue through the interface modification,perovskite film formation control and composition engineering based on the planar p-i-n structure of PSCs with low hysteresis effect and low temperature process in this dissertation.And some important conclusions are achieved.The detailed research contents and main achievements of this dissertation are as follows:?1?The method of interface modification by polyelectrolyte PEIE for planar p-i-n structure PSCs is proposed.And it is shown that PEIE interface modification interlayer can effectively improve the photovoltaic properties of perovskite solar cells by the results of experiments.A large number of research results indication that the PCE of planar p-i-n structure PSCs can be increased from 11.01%to 13.99%by inserting 8 nm PEIE interface modification interlayer between the electron transport layer PC₆₁BM and the metal electrode Ag,and the PCE increased by 27%.We also optimize the solvent for PEIE.We chose isopropanol?IPA?with a relative low polarity index of 3.9 as the PEIE solvent,instead of the usually used 2-methoxyethanol or methanol.Through the stability test for 200 hours,it was found that the devices with PEIE interlayer enhanced their stability by more than 40%relative to the control devices.?2?The calculation results by result of UPS test show that the PEIE interlayer can decrease the energy offset between PC₆₁BM and Ag electrode.The mechanism of the improvement about the energy offset is been carefully analyzed.We also study the recombination mechanism with and without PEIE interlayer by measuring V_OC and J_SC at various sun light intensities from 100 to 0.1 mW/cm².It is shown that the PEIE interlayer can suppress the trap-assisted recombination and enhance the probability of the charge carries collection.?3?The process of preparation perovskite film by solvent engineering is optimized.A mixed solution of toluene and diethyl ether is innovatively proposed as anti-solvent to improve the crystal quality of the perovskite film and the photoelectric properties of the PSCs.The experimental results show that when the volume ratio of the mixed solution of toluene and diethyl ether is 1:1,the photoelectric performance of perovskite film is optimal.Through optimizing the ratio of the mixed anti-solvent,the PCE of the PSCs is improved by 11%relative to the control devices.The planar p-i-n PSCs with a structure of Glass/ITO/PEDOT:PSS/CH₃NH₃PbI₃/PC₆₁BM/BCP/Ag are prepared with the best PCE exceeding 15%.It is shown that the crystalline quality of the perovskite film and the film coverage is related to the volatility of anti-solvent.Therefore,the use of solvent engineering preparation of perovskite film should be carefully chosen anti-solvent type.?4?The composition engineering of perovskite is researched for the further enhancement of photoelectric properties and thermal stability of planar p-i-n PSCs.The annealing conditions of the MA_0.7FA_0.3Pb(I_0.9Br_0.1)₃ perovskite films are optimized at 100?for 30 minutes by the results of experiments and a series of characterization methods.The MA_0.7FA_0.3Pb(I_0.9Br_0.1)₃ perovskite films have the best quality of crystallization under this conditions.The corresponding mixed lead halide PSCs is prepared with a structure of Glass/ITO/PEDOT:PSS/MA_0.7FA_0.3Pb(I_0.9Br_0.1)₃/PC₆₁BM/BCP/Ag and the PCE of more than 16%.In addition,the thermal stability of the relevant perovskite film is also investigated.The experimental results show that the mixed perovskite films based on 30%CH?NH₂?₂⁺cation and 10%Br^-anion obviously increased the stability of the perovskite film at high temperature relative to the conventional MAPbI₃ films.The thermal stability of devices also significantly improved.The PCE of the MA_0.7FA_0.3Pb(I_0.9Br_0.1)₃ PSCs remain 70.0%of the original value,while the PCE of the MAPbI₃ PSCs significantly decreased to 46.5%of their original at 80?for 24 hours.?5?Taking the advantages of low temperature process for the planar p-i-n structure PSCs and using the previous research results in the composition engineering of perovskite,the flexible PSCswiththestructureofPEN/ITO/PEDOT:PSS/MA_0.7FA_0.3Pb(I_0.9Br_0.1)₃/PC₆₁BM/BCP/Ag are prepared on flexible PEN substrate.Through multiple cycles of bending tests with the bending radius of 8 mm,the flexible PSCs still maintain about 85%of their initial PCE after 1000 bending cycles.These results demonstrate that these mixed-lead halide(MA_0.7FA_0.3Pb(I_0.9Br_0.1)₃)possess excellent mechanical reliability.The high-performance planar p-i-n perovskite solar cells were prepared,and the relevant mechanism was analyzed in depth and conclusive results were obtained.The performance of perovskite solar cells prepared reached the international advanced level in the same period and made a certain contribution to the industrialization of perovskite solar cells.