Research On Defect Passivation And Regulation Of Flexible Perovskite Solar Cells

Perovskite solar cells(PSCs)have attracted attention from both researchers and market participants owing to their high power conversion efficiency(PCE),easy fabrication,low costs,potential to be utilized in the form of flexible solar cells and many other advantages.Among them,flexible perovskite solar cells(FPSCs)are especially more widely studied attributing to their unique properties,including being lightweight and wearable,which meet the requirements of future electronic devices.However,the PCE of FPSCs is apparently lower than that of rigid perovskite solar cells(RPSCs),due to the low light transmittance,poor high-temperature resistance,and poor acid resistance of flexible substrates,as well as various defects induced by the low-temperature fabrication process and bending stress on the device during fabrication and testing.In this dissertation,through passivating the defects in functional layers and their interfaces in FPSCs devices based on PEN/ITO flexible substrate and n-i-p structure,strategies for defect passivation and regulation at interfaces and grain boundaries are presented,in order to fabricate efficient and stable FPSCs and further promote the development of FPSCs.The following research on defect passivation of functional layers and their interfaces in FPSCs devices has been carried out.(1)HCl is added in the colloidal aqueous solution of commercial SnO2 quantum dots.There are defects on SnO2 quantum dots due to their small size,large specific surface area and unpaired dangling bond on the surface.Chloride ion(Cl-)effectively passivates oxygen vacancy sites and hydroxyl defects by being absorbed on the oxygen vacancy sites on the surface of SnO2 quantum dots,so as to improve the VOC and FF of devices.XRD shows that the addition of HCl will not affect the crystallization and grain size of the original SnO2 quantum dots.In addition,the testing results based on Raman,FTIR,PL,SCLC,EIS confirmed that the defects on the surface of SnO2 quantum dots have been passivated effectively with the addition of HC1.After adding HC1,the SnO2 quantum dots film can be prepared at a low temperature of 60℃.As a result,VOC=1.097 V,JSC=23.11 mA/cm2,FF=79.54%,and PCE=20.17%were obtained for the FPSCs in the experimental group,while VOC=1.113 V,Jsc=23.06 mA/cm2,FF=79.06%,and PCE=20.29%were achieved for the FPSCs prepared by ETL annealed at 120℃ for 30 min.Through the addition of HC1,the application of commercial SnO2 in FPSCs is further optimized.(2)Fluorographene quantum dots(FGQDs)with particle sizes ranging from 2 to 8 nm,are exfoliated from graphite fluoride with the aid of stirring and sonication.Then,FGQDs are added into the perovskite precursor solutions for the preparation of perovskite polycrystalline films to passivate perovskite crystal defects.The FGQDs possess a high content of fluorine,which is favorable to passivating the grain boundaries and film surface and suppressing the ion migration through the interaction between the F atoms and the exposed ions and groups of the perovskite films.The perovskite film with the FGQDs shows lower carrier trap densities and enhanced hole mobility,which lead to significant improved VOC and FF.As a result,a champion PCE of FPSCs as high as 20.40%,and VOC=1.106 V,JSC=22.87 mA/cm2,FF=80.67%.With the addition of FGQDs,the hydrophobicity of the perovskite film is increased and the environmental stability is enhanced.(3)Artemisinin molecules were added into the perovskite precursor solution,for the preparation of perovskite polycrystalline films with lower defect concentrations.The experimental results showed that artemisinin has a good passivation effect on perovskite films.The mechanism is that the artemisinin molecule,as a Lewis base,passivates the defects of perovskite polycrystalline films via the interaction between the carbonyl groups and uncoordinated Pb ions.Theoretical calculations also indicated the binding energy between artemisinin molecules and uncoordinated Pb ions can reach 42.9 KJ/mol,which can effectively suppress the formation of deep-level defect traps and effectively suppress non-radiative recombination in perovskite polycrystalline films.As a result,FPSCs incorporating artemisinin(0.22 mol%)demonstrated an outstanding PCE of 21.10%,and VOC=1.126 V,JSC=23.32 mA/cm2,FF=80.35%.In addition,artemisinin-doped FPSCs exhibited enhanced long-term stabilities under different conditions.The incorporation of artemisinin was found to improve the environmental stability of perovskite films significantly.The passivation of defects could suppress ion migration and significantly improve the thermal and optical stability of FPSCs.(4)There are more defects on ITO surface on flexible polymer substrate due to low-temperature fabrication process and substrate flexibility.Therefore,the defect passivation on ITO/ETL interface also plays an important role in FPSCs defect passivation.A molecular layer of polyether amine(D-230)is modified at the ITO/SnO2 interface of the PEN substrate to form an ultra-thin tunneling passivation layer.The lone pair electrons in the ether bond of D-230 molecule interact with the positive charges(such as dangling bonds of Sn4+and In3+)on the ITO surface to effectively passivate ITO surface defects through the Lewis acid-base mechanism.Conductive AFM shows that D-230 with a concentration of 0.175 mg/mL can basically cover the ITO surface.The SEM cross section of the device shows that the D-230 molecular layer is an ultra-thin insulating layer.Characterization testing based on SCLC,TPV,EIS,M-S and PL shows that D-230 passivates the defects at ITO/SnO2 interface,reduces the non-radiative recombination of carriers at this interface,promotes the effective extraction of carriers,and improves VOC and FF of FPSCs.As a result,VOC=1.148 V,Jsc=22.98 mA/cm2,FF=80.40%,and PCE=21.21%were obtained for the high-efficiency FPSCs.