The Technology Research Of High-efficient Perovskite Solar Cells

Inorganic-organic halide perovskites have become of interest due to their excellent merits in optoelectronic properties,such as high absorption coefficient,adjustable direct band gap,ambipolar transportation and small exciton binding energy.In the past few years,perovskite solar cells have developed rapidly with its photoelectric conversion efficiency increased from 3.8%to 22.1%.This rapid increase of efficiency is attributed to the device structure development,fabrication process optimization,charge transport layer selection and the interface engineering.Thus,the interface optimization and the quality of active layer have been research hotspot in the field of perovskite solar cells.This article was based on the material system of CH3NH3PbI3,using the device structure of FTO/c-TiO2/m-TiO2/CH3NH3PbI3/spiro-OMeTAD.Firstly we have systematically studied the effects of mesoporous TiO2 layer interface optimization on the photoelectric properties of perovskite solar cells.Then we have optimized the preparation methods of CH3NH3PbI3 film.Finally,Cl was introduced into the perovskite by adding MAC1 to the MAI solution.The dependence of the Cl chemical state on the MACl concentration,the thermal annealing parameters and the location in the perovskite film were investigated.And we also researched the effects of Cl on the photoelectric properties of perovskite solar cells.The main experimental results were as follows:1.We have optimized the interface between mesoporous TiO2 and the perovskite film by the Li-treatment of mesoscopic TiO2.The experimental results showed that Li was doped into the TiO2 film,and the Li-treated mesoscopic TiO2 film had a better surface flatness.The research indicated that the mobility of electron was improved by the Li-treatment of mesoscopic TiO2.Therefore,the power conversion efficiency was enhanced from 9.3%to 12,7%,the Jsc and Voc and FF were significantly improved.2.Perovskite films were prepared using a two-step spin-coating method.We mainly optimized the preparation process of PbI2 and CH3NH3PbI3 film.(1)The effects of the PbI2 spin-coating speed on the PbI2 film quality was investigated.The experimental results showed that when the spin-coating speed was 3000 r/min,the solar cell efficiency was the highest.(2)A strongly coordinative solvent of dimethyl sulfoxide(DMSO)was introduced into the dimethylformamide(DMF)precursor solution of PbI2.The effects of DMF/DMSO combined solvent volume ratio(4:1,5:1,9:1)on the PbI2 film quality was investigated.The results revealed that when the solvent volume ratio of DMF and DMSO was 5:1,the good PbI2 architecture was formed on the basis of the higher crystallinity of PbI2,and the efficiency of perovskite solar cell was improved.(3)We studied the effects of MAI/IPA precursor solution concentration on the CH3NH3PbI3 film quality.We found that when the MAI/IPA precursor solution concentration was 50 mg/mL,the solar cell efficiency was the highest.(4)The residual amount of PbI2 can be regulated by changing the spin-coating speed of the MAI.Moderate residual PbI2 acted as a blocking layer between the TiO2 semiconductor and the perovskite,reducing the probability of electron transfer back and charge recombination,eventually improving the photoelectric properties of solar cells.The power conversion efficiency achieved 15.90%(measured under standard AM1.5G test conditions)with a Jsc of 19.74 mA/cm2,a Voc of 1.10 V,and an FF of 73.2%.3.Perovskite films on mesoporous TiO2 scaffolds were prepared using a two-step method,and chloride was introduced into the perovskite by adding MACl to the MAI solution.The dependence of the Cl chemical state on the MACl concentration,the thermal annealing parameters,and the location in the perovskite were investigated.At low MACl concentrations,the chloride ions were in the form of CH3NH3PbI3-xClx,while both CH3NH3PbI3-xClx and CH3NH3PbCl3 coexisted in the perovskite film following the use of high concentrations.Upon thermal annealing,chloride tended to leave the perovskite,since both CH3NH3PbI3-xClx and CH3NH3PbCl3 decompose,and the only product was CH3NH3PbI3 at annealing times longer than 50 min.Interestingly,the depth distribution of chloride in the perovskite as determined by XPS showed that chloride was present at the perovskite/TiO2 interface and also in the upper capping layer.However,the binding energy between Cl and Ti at the interface was strong,which tended to stabilize the chloride in the perovskite,while the chloride in the capping layer tended to escape upon thermal annealing.The introduction of MACl improved the perovskite crystallinity,the perovskite film surface coverage,the electron injection efficiency and the photoelectric conversion efficiency.A MACl concentration of 2 mg/mL gave the maximum efficiency of 18.98%,with a Jsc of 23.29 mA/cm2,a Voc of 1.10 V,and an FF of 74.3%.