Preparation And Optimization Of All-perovskite Tandem Solar Cells

In recent years,the photoelectric conversion efficiency(PCE)of perovskite solar cells(PSCs)has exceeded 25%.However,According to Shockley-Queisser's limitations,the room for efficiency improvement of single-junction perovskite solar cells is very limited..Therefore,the development of tandem solar cells is an important way to break the limit and further improve the efficiency of PSCs.Tandem solar cells are generally composed of two or more sub-cells.We broaden the absorption range of the solar energy spectrum by using semiconductor materials with different band gaps in the sub-cells,and finally achieve the effect of improving the conversion efficiency of the battery.Compared with other tandem cells,all perovskite tandem solar cells have unique advantages,including the perovskite material band gap can be adjusted in a wide range,and the absorption coefficient and mobility are high;based on the same band gap light-absorbing material Among the sub-cells,the perovskite cell has higher photoelectric conversion efficiency,can be prepared at low temperature,and has a lower manufacturing cost.In this paper,Sn-doped Pb narrow-bandgap perovskite material and Br-doped wide-bandgap perovskite material are used as light-absorbing materials for the bottom cell and top cell of the tandem cell,respectively.Four-terminal all perovskite solar cells are prepared by mechanical stacking.The main research contents are as follows:(1)Preparation of the bottom cell of the laminated cell.By replacing Pb with Sn,The ratio of Sn and Pb is 1:1,and the(FASn I₃)_0.5(MAPb I₃)_0.5perovskite light-absorbing layer with a band gap of 1.23e V is prepared.10%Sn F₂ and metal Sn powder are used as additives to inhibit the oxidation of Sn²⁺and reduce Sn⁴⁺to Sn²⁺.On this basis,by optimizing the precursor solution concentration,cation doping and annealing temperature,a light-absorbing layer with a thickness of 800 nm was prepared.The final prepared single-junction narrow band gap(1.23 e V)perovskite battery ITO/PEDOT:PSS/(FASn I₃)_0.5(MAPb I₃)_0.5/C₆₀/BCP/Ag V_oc is 0.68 V,J_sc is 32.36 m A/cm²,FF is63.53%,PCE is 13.96%.(2)Preparation of semi-transparent top cell of laminated cell.By replacing I with Br,The ratio of Br to I is 0.8:2.2,and a perovskite light-absorbing layer of MAPb Br_0.8I_2.2 with a band gap of 1.74e V is prepared.The preparation conditions of the hole transport layer(Ni O_x)were optimized.Based on this,the source of Br in the precursor solution,the concentration of the precursor solution and the solvent ratio were optimized.Finally,a battery ITO/Ni O_x/MAPb Br_0.8I_2.2/C₆₀/BCP/Ag with V_oc of 1.09V,J_sc of 18.49 m A/cm²,FF of 65.07%,and PCE of 13.08%was obtained.On the basis of this opaque top cell,a translucent perovskite top cell ITO/Ni O_x/MAPb Br_0.8I_2.2/C₆₀/BCP was prepared by introducing a high transmittance Ag/Mo O₃ interface buffer layer and using ITO as a transparent top electrode.Its V_oc is 1.07 V,J_sc is 13.23 m A/cm²,FF is 69.95%,and the final PCE is 9.86%.In addition,a comparative cell was prepared,namely MAPb Cl_0.1I_2.9 opaque cell ITO/Ni O_x/MAPb Cl_0.1I_2.9/C₆₀/BCP/Ag based on low band gap(1.56 e V)and translucent cell ITO/Ni O_x/MAPb Cl_0.1I_2.9/C₆₀/BCP/Ag(1 nm)/Mo O₃(3 nm)/ITO/Ag achieved efficiencies of 18.41%and 8.49%,respectively.(3)The assembly of tandem all perovskite solar cells.Two 4-T tandem cells were prepared by mechanically stacking the bottom cell and semi-transparent top cell obtained in steps 1 and 2 with ITO/PEDOT:PSS/(FASn I₃)_0.5(MAPb I₃)_0.5/C₆₀/BCP/Ag As the bottom cell,ITO/Ni O_x/MAPb Br_0.8I_2.2/C₆₀/BCP/Ag(1 nm)/Mo O₃(3 nm)/ITO/Ag and ITO/Ni O_x/MAPb Cl_0.1I_2.9/C₆₀/BCP/Ag(1 nm)/Mo O₃(3nm)/ITO/Ag as the top cell,obtained efficiencies of 15.56%and 13.39%,respectively.