Modulating titanium dioxide electron transport layer by self-doping for high-efficiency carbon-based perovskite solar cells

In perovskite solar cells (PSCs), it is important to construct electron transport layer (ETL) with ideal surface morphology and advantageous electron transport dynamics. In this work, a functional TiO₂ ETL is designed and constructed based on a novel Ti³⁺ self-doping strategy. Experimental results indicate that Ti³⁺ dopant can optimize TiO₂ film crystallization process by facilitating the assembly of precursor particles, reducing the content of pore-forming reagent, and enhancing the adhesion of precursors to glass substrate in film formation process. Therefore, the modified surface morphology inhibits the formation of undesired hole structure. Besides, self-doping moderately generates oxygen vacancies on TiO₂ surface and a shallower TiO₂ Fermi energy level. These not only result in a stronger interfacial electronic coupling, but also establish an advantageous energy band alignment. These merits optimize interfacial electron transfer dynamics by inhibiting recombination loss and facilitating electron extraction. Benefiting from the optimized TiO₂ ETL, hole transport layer (HTL)-free carbon electrode based CsPbI₃ PSCs deliver a high efficiency of 18.62%, representing one of the highest levels in this field.