Studies On The Fabrication And Interface Modification Of Organolead-halide Perovskites Photovoltaic Devices

Recently,one emerging photovoltaic technology called perovskite solar cells,which are based on CH₃NH₃PbI3 and its analogues,have received increasing attention.In the eight years since 2009,the highest photovoltaic conversion efficiency of these perovskite solar cells has been increased from 3.8% to 22.1%.This efficiency does not only exceed the record value of the other emerging photovoltaic technologies like dye-sensitized solar cells,but also is no less than some well-developed industrialized photovoltaic technology like polycrystalline silicon solar cell.During the rapid development of perovskite solar cells,the improvement of the fabrication process of the perovskite materials to a better film and the modification of the related interface have been proved effectively to improve the device efficiency.In this dissertation,the fabrication process of the perovskite film by two-step spin coating method and the modification of the interfaces related to the perovskite film has been investigated.The main works of this paper are following:?1?A thin wide band gap organic semiconductor N,N,N',N'-tetraphenyl-benzidine layer has been introduced by spin-coating to engineer the metal-semiconductor interface in the hole-conductor-free perovskite solar cells.The average cell power conversion efficiency?PCE?has been enhanced from 5.26% to 6.26% after the modification and a highest PCE of 6.71% has been achieved.By the analysis of electrochemical impedance spectroscopy?EIS?and dark current data,it is revealed that this modification can increase interfacial resistance of CH₃NH₃PbI3/Au interface and retard electron recombination process in the metal-semiconductor interface.?2?A morphology-controlled CH₃NH₃PbI3-xClx film is synthesized via two-step solution deposition by spin-coating a mixture solution of CH₃NH₃ Cl and CH₃NH₃ I onto the TiO2/PbI2 film for the first time.It is revealed that the existence of CH₃NH₃ Cl is supposed to result in a preferential growth along [110] direction of perovskite,which can improve both of the crystallinity,surface coverage of perovskite and reduces the pinholes.13.12% of power conversion efficiency has been achieved for the mesoscopic cell,higher than 12.08% of power conversion efficiency of the devices fabricated without CH₃NH₃ Cl via the same process.The improvement mainly lies in the increasing open-circuit photovoltage which is ascribed to the reduction of reverse saturation current density.Furthermore,the formation process of CH₃NH₃PbI3-xClx perovskite is explored,in which one intermediate containing chlorine that changes the reaction mechanism are suggested to exist by controlled experiment.?3?The influence of moisture existing during the fabrication process of perovskite in two-step spin coating method is investigated.It is found that moisture can activate the reaction of PbI2 and CH₃NH₃X(X=I?Cl,which totally can turn the reactants into final perovskite without heating.It is found by XRD analysis that there is a precursor complex is formed with H2 O during the rapid reaction process.Moreover,this precursor complex has a great number of defect leading to heavy surface charge recombination of the perovskite film,thus reducing the efficiency of the device.However,this precursor complex with H2 O can be removed after annealing and the performance of the devices fabricated under 40% RH can be significantly enhanced to 13.63% and over 12% in steady state for CH₃NH₃PbI3 while 15.50% and over 14% in steady state for CH₃NH₃PbI3-xClx,respectively.