Preparation Of Perovskite Heterojunction Solar Cells Based On Graphene Materials And Their Photoelectric Properties

Perovskite is a kind of material with calcium titanate crystal structure,and its chemical formula can be expressed by ABX3.It has excellent photoelectric properties such as high absorption coefficient,appropriate band gap,long electron diffusion length,bipolar conductivity and high carrier mobility.Because of these unique characteristics,it has a good application prospect in the field of solar cell and photodetector.The most important method to prepare perovskite solar cells is to prepare perovskite absorber.And specific preparation process is through the PbI2(or PbC12,PbBr2)and MAI material mixed according to certain proportion,then dissolved in DMF solvent(DMSO,GBL,etc),the formation of perovskite precursor solution,and then through the uniform rubber suspension with the solution in the preparation of good electron transport layer(ETM)and hole transport layer(HTM),and annealing treatment,the film formation of perovskite crystal film.Although the preparation process of one-step method is simpler,but the preparation of the perovskite membrane is bad control,prone to film thickness is not uniform,caused by light absorption layer surface will appear more defect mode in the preparation of the electronic transport layer and hole transport layer will cause bigger exciton compound near the interface,is not conducive to promote the efficiency of solar cells.For perovskite solar cell performance,the influencing factors are mainly from two aspects.One is the crystallization inside the perovskite absorber and the surface condition,which will affect the generation of carriers and composite.Another important factor is the interface transport layer between the perovskite absorber and the electrode.As far as perovskite heterojunction solar cells are concerned,there are two kinds of interfacial modification:anode interfacial modification and cathode interfacial modification.In this paper,the main research is the anodic interface layer modification.There is a hole transport layer between the active layer of perovskite and the anode.At present,most devices use PEDOT:PSS as the hole transport material,and such materials can effectively transport the holes,and the device preparation process is simple.But the PEDOT:PSS as hole transport layer there is a problem,and PEDOT:PSS in the effective transmission of holes at the same time,they cannot be effective to the electronic shielding,this will lead to produce light raw electronic some through hole transport layer to the anode,compound with the hole,cause damage.This will have a great impact on the photoelectric current of the device,which will reduce the PCE of the battery.After the anode interface modification material GO is introduced,a potential barrier can be generated at the LOME end to prevent the electrons from moving towards the anode.First of all,in order to improve the surface problem of perovskite film prepared by one-step method,in the process of suspended coating film,ethyl acetate and other solvents were used instead of toluene as the extraction agent to rinse the film surface,extract the excess solvents in the solution of perovskite precursor,and prepare the perovskite film with smooth surface.In order to achieve the high photoelectric conversion efficiency of perovskite solar cells,it is necessary to prepare perovskite crystals with large grain size,uniform and no voids.In this preparation process,we carried out detailed optimization of the equipment's rotation speed,suspension coating time,addition of extractant and extraction of vacuum.Secondly,to solve the problem of carrier recombination at the anode interface,GO was introduced as the interface modification material to optimize the level matching of the device.In the subsequent experiments,we adjusted the thickness of GO by controlling the number of layers of the overcoat to find the best preparation parameters.In this process,the perovskite thin film was characterized by scanning electron microscope,X-ray diffractometer and other devices to ensure that the quality of the thin film was not greatly affected after the introduction of GO.Finally,we improved the photoelectric conversion efficiency of perovskite solar cells from 11.4%to 14.1%.We then transferred a monolayer of graphene onto the substrate and deposited a thin film of PbTe crystals on it using electrochemical atomic beam epitaxy.We used a 5mM Pb(CH3COO)2-10mMTeo2-200Mm NaOH system to control the deposited PbTe film by regulating the deposition potential during the growth process and the type of substrate.Then EDS,XRD and other characterization methods were used to compare the quality of films deposited under different conditions,and it was found that the film deposited at-0.8v voltage had the best quality.On this basis,we prepared graphene/PbTe/perovskite heterojunction solar cells and tested their photoelectric properties.Compared with devices without PbTe materials,the photoelectric conversion efficiency of the battery increased from 6.6%to 9.7%.