Defect passivation by alcohol-soluble small molecules for efficient p–i–n planar perovskite solar cells with high open-circuit voltage

Abstract

Solution-processed perovskite films inevitably have a number of ionic defects, regarded as non-radiative recombination centers, which limit the overall efficiency and the stability of perovskite solar cells (Pero-SCs). Passivation of these defects has been proven to be an efficient strategy to suppress the charge recombination and thus improve the performance of Pero-SCs. Herein, for the first time, a π-conjugated and alcohol-soluble small molecule with bilateral carboxyl and thiophene groups, namely 2,5-di(thiophen-2-yl)terephthalic acid (DTA), was introduced into the MAPbI_3−xCl_x (MA = CH₃NH₃) film to passivate the defects and enhance the performance of the corresponding planar p–i–n Pero-SCs. With high electron density, the symmetric carboxyl groups on both sides of DTA can effectively coordinate with unsaturated Pb²⁺ cations to passivate the defects in the perovskite. This efficient defect passivation can reduce the charge trap density and increase the carrier lifetime, which leads to a significant enhancement of the open-circuit voltage from 1.07 V for the control Pero-SC to 1.17 V for the passivated one, resulting in a power conversion efficiency (PCE) of 21.45%. The highest achieved V_oc reaches 1.19 V, with a PCE of 21.40%, and the corresponding loss of V_oc is only 0.38 V. In addition, the DTA passivated devices exhibit a photovoltaic performance with high reproducibility, as well as a significant improvement in environmental stability and thermal stability. This work demonstrates the great potential of DTA as an effective and promising additive to passivate the perovskite defects for the high performance of Pero-SCs.