Surface n-doping for perovskite solar cells with simultaneously enhanced efficiency and oxygen stability

Introducing moderate iodide vacancies in halide perovskites has been frequently observed to form n-type doping effect and optimize the power conversion efficiency (PCE) of perovskite solar cells (PSCs). However, it has been widely recognized that iodide vacancies are mobile and photochemically detrimental. Herein, tris(2-aminoethyl)amine (TAEA), a branched molecule containing three primary amino groups and one tertiary amino group, is reported to passivate the undercoordinated Pb²⁺ ions and meanwhile n-dope the perovskite surface with its multiple amino groups. After TAEA post-treatment, the PSCs show robustly improved fill factor (FF) from 76.2% to 82.9%, improved open-circuit voltage (V_OC) from 1.08 to 1.16 V, and enhanced PCE from 19.4% to 23.4%. Moreover, the oxygen stability of the TAEA treated perovskite film has been substantially improved simultaneously, which is essentially different from the decreased oxygen stability in the case of using iodide vacancy as the n-dopant. Benefited from the iodide vacancies filling effect by TAEA, the activation energy (E_a) of ions migration in perovskites also increased from 0.43 to 0.67 eV.