Studies Of Single-junction And Tandem Perovskite Solar Cells Based On Polymer Electrode

Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate)(PEDOT:PSS)is a novel conducting polymer with excellent environmental stability,high conductivity and transparency.This thesis focuses on fabricating efficient single-junction and tandem perovskite solar cells via developing PEDOT:PSS electrode.Details are as follows:Firstly,developing vacuum-free,solution-processible low-cost electrode to replace traditional metal electrode is of great significance to lower the threshold of commercial applications of perovskite solar cells.In this study,we use solution-processible conductive polymer PEDOT:PSS to replace traditional metal electrode.The PEDOT:PSS electrode is prepared via film transfer technique,which circumvents the incompatibility between aqueous PEDOT:PSS solution and water-sensitive perovskites.With CH₃NH₃Pb I₃ perovskite as the light-absorbing layer,we fabricate perovskite solar cells that are vacuum-free and all-solution-processed.The as-prepared solar cells,with device structure of glass/FTO/c-Ti O₂/m-Ti O₂/MAPb I₃/spiro-OMe TAD/PEDOT:PSS,yield an optimal power conversion efficiency of 11.29%.Secondly,to improve the efficiency of perovskite solar cells with PEDOT:PSS top electrode,we prepare high-quality perovskite films by introducing the synergistic effect of excess Pb I₂ and Cl incorporation in the precursor solutions,which significantly boosts the open-circuit voltage of perovskite solar cells.For Ti O₂ electron transporting layer and spiro-OMe TAD hole transporting layer based n-i-p solar cells,the optimal open-circuit voltage increases from 1.08 V to 1.15 V(an increase of 70 m V);for PEDOT:PSS hole transporting layer and PCBM electron transporting layer based p-i-n solar cells,the optimum open-circuit voltage increases from 1 V to 1.16 V(an increase of 160 m V).Further characterizations show that the synergistic effect of excess Pb I₂and Cl incorporation effectively enhances the photoluminescence intensity and carrier lifetime,while benefits the growth of perovskite crystals.Based on these high-quality perovskite films,the efficiency of MAPb I₃(Cl)perovskite solar cell with PEDOT:PSS top electrode increased from?11%to over 16%.Thirdly,owing to the aforementioned film-transfer technique to prepare PEDOT:PSS film and it's high transparency,we develop a novel charge recombination layer(CRL)consisting of spiro-OMe TAD/PEDOT:PSS/PEI/PCBM:PEI to fabricate two-terminal perovskite/perovskite tandem solar cells.The CRL satisfies four basic requirements:(1)large work function contrast between the bottom and the top surfaces for hole and electron-collection;(2)low-temperature processing;(3)orthogonal solvents;(4)robust enough to prevent solvent penetration.Eventually,we fabricate two-terminal bottom-up solution-processed perovskite/perovskite tandem solar cells with open-circuit voltage of?1.9 V,almost equals to the sum of the two sub-cells(?1V).We also fabricate two-terminal bottom-up organic/perovskite tandem solar cells with CRL comprising PEDOT:PSS/PEI/PCBM:PEI.The open-circuit voltage of the as-fabricated devices reaches?1.84 V,also almost equals to the sum of the two sub-cells.Finally,we find that Cl incorporation not only improves the film quality of Pb-based perovskites,but also induces the phase transformation of Sb-based Pb-free MA₃Sb₂Cl _XI_9-X perovskites from zero-dimensional dimer phase to two-dimensional layered phase.The critical point for the phase transformation occurs when the atom ratio of Cl/I in the precursor solution is in the range of 0.22-0.25.Further analysis on the bandgap,electronic structure and film morphology of zero-dimensional and two-dimensional MA₃Sb₂Cl _XI_9-X suggests that two-dimensional MA₃Sb₂Cl _XI_9-X is more suitable for photovoltaic application.Perovskite solar cells(device structure:glass/FTO/c-Ti O₂/m-Ti O₂/MA₃Sb₂Cl _XI_9-X/spiro-OMe TAD/PEDOT:PSS)based on the two-dimensional MA₃Sb₂Cl _XI_9-X perovskites achieve an optimal power conversion efficiency of?2.19%,which is the record efficiency of Sb and Bi based perovskite solar cells.More importantly,the solar cell devices exhibit very good air stability and almost no hysteresis behavior can be observed.