In Situ Oxidative Polymerization of PEDOT, Reducing the TBP Dosage, and Synergizing with Spiro-OMeTAD to Enhance the Efficiency and Stability of Perovskite Solar Cells

Although the efficiency of perovskite solar cells (PSCs) keeps breaking new records, their stability and cost are still limited by using the conventional hole transport material of 2,2',7,7'-tetrakis(N,N-di-p-methoxyphenylamine)-9,9'-spirobifluorene (Spiro-OMeTAD). Herein, we use 3,4-ethylenedioxythiophene (EDOT) as a solubilizer to enhance the dissolution of lithium bis(trifluoromethane)sulfonylimide (Li-TFSI) and reduce the 4-tert-bultypyridine (TBP) dosage. Then, EDOT undergoes in situ oxidative polymerization to generate PEDOT by an oxidizing agent of iodine (I₂). Moreover, I₂ can also accelerate the oxidation of Spiro-OMeTAD. Therefore, the generated PEDOT can synergistically enhance hole transport capability with the oxidized Spiro-OMeTAD, and the generated I^- ions can compensate for the I vacancies and inhibit the migration of I^- in the perovskite film, resulting in an enhanced stability and efficiency of PSCs. A PSC based on the composite hole transport system achieves a power conversion efficiency (PCE) of 24.79%. Moreover, the PSC retains 92% of its initial PCE for over 2000 h under ambient conditions of 25 °C and 35% relative humidity. Furthermore, the quantities of Spiro-OMeTAD and TBP have, respectively, decreased by 24.9 and 37.5% in the composite hole transport system, thereby lowering the production cost of the PSC and facilitating its industrialization development.