| The solution-processable metal halide perovskite solar cells（PSCs）developed rapidly in recent years and have been widely recognized as the typical representative of low-cost solar cell technology.The printable mesoscopic perovskite solar cells（p-MPSCs）based on the porous triple layers of Ti O2/Zr O2/carbon could further reduce the material cost and process cost of PSCs.The challenge faced by p-MPSCs is that their power conversion efficiency（PCE）still lags behind that of conventional PSCs,which is mainly due to the recombination loss of carriers in the Zr O2 spacer and at the perovskite/carbon electrode interface.In this thesis,efforts were made to optimize the carrier dynamics process in p-MPSCs,reduce the recombination loss,and improve the device performance,through the development of spacer materials and the regulation of perovskite/carbon electrode interface.The main contents include:（1）A new spacer based on barium titanate（BTO）ferroelectric material was developed.Through the ameliorated solvothermal synthesis method,controllable preparation of ferroelectric BTO nanoparticles with proper size,good dispersion and regular morphology were achieved.Through the adjustment of the ingredients,a well-dispersed BTO paste was obtained.Smooth and uniform BTO porous films were thus prepared and successfully applied as the spacer in p-MPSCs.The experiment results showed that BTO had excellent insulation property and can effectively reduce the recombination loss in the spacer layer.The open circuit voltage(VOC)of 1μm-thick-BTO spacer based p-MPSCs is comparable to that of 3μm-thick-Zr O2 spacer based p-MPSCs.An average PCE of 12.92%was obtained with 1μm-thick-BTO spacer consisting of 30 nm nanoparticles.（2）The influence of ferroelectric polarization of BTO spacer on the performance of p-MPSCs was investigated.The polarization characteristics of the prepared BTO porous films were verified by electrical tests.Different remnant polarization in the BTO layer could be obtained via tuning the direction,strength and period of the external bias voltage applied to it.It was found that negative polarization improved the performance of p-MPSCs,while positive polarization reduced it.Through transient photovoltage and transient photocurrent measurements,it was analyzed that polarization can induce the formation of dipoles between at the perovskite/carbon and the perovskite/Ti O2interfaces,thus affecting the carrier dynamics process.The appropriate polarization can promote the carrier transport and inhibit carrier recombination.This work exhibited the significance of functionalizing the spacer with ferroelectric polarization.Based on negative polarization,the average PCE of BTO-based p-MPSCs was increased from 12.92%to 14.05%.（3）The interface modification technology based on halogen bond interaction was developed.The 2-bromo-6-fluoronaphthalene（BFN）was introduced into p-MPSCs by post-treatment engineering,which interacted with undercoordinated iodine ion in perovskite through the bromine atom via halogen bond.The electron withdrawing ability of fluorine atom and the conjugation property of naphthalene enhanced the reaction between Br and I-,achieving effective defect passivation.The analysis showed that the introduction of BFN promoted the extraction of holes near the interface between perovskite and carbon electrode,reduced the recombination,and thus improved the PCE of p-MPSCs from 15.50%to16.77%.（4）The Fermi level（EF）of perovskite adjacent to carbon electrode was effectively regulated.The EF of halide perovskite was down-shifted by introducing thiol-containing cysteamine hydrochloride（CSA-Cl）into p-MPSCs.The ultra-violet photoelectron spectroscopy results showed that,combined with the strong interaction between Pb and S and the thiol oxidation process,CSA-Cl significantly reduced the EF of perovskite from-4.53 e V to-5.22 e V.An optimized energy level alignment in p-MPSCs was achieved,which enhanced the selectivity of charge extraction at the interface between perovskite and carbon electrode,and realized the improvement of PCE from 17.20%to 17.74%.This work provided a feasible technical scheme for energy level regulation of halide perovskites. |
