Efficient Defect Passivation for Perovskite Solar Cells by Controlling the Electron Density Distribution of Donor-π-Acceptor Molecules

Organic-inorganic hybrid perovskite solar cells (PSCs) are a promising photovoltaic technology that has rapidly developed in recent years. Nevertheless, a large number of ionic defects within perovskite absorber can serve as non-radiative recombination center to limit the performance of PSCs. Here, organic donor--acceptor (D--A) molecules with different electron density distributions are employed to efficiently passivate the defects in the perovskite films. The X-ray photoelectron spectroscopy (XPS) analysis shows that the strong electron donating N,N-dibutylaminophenyl unit in a molecule causes an increase in the electron density of the passivation site that is a carboxylate group, resulting in better binding with the defects of under-coordinated Pb2+ cations. Carrier lifetime in the perovskite films measured by the time-resolved photoluminescence spectrum is also prolonged by an increase in donation ability of the D--A molecules. As a consequence, these benefits contribute to an increase of 80 mV in the open circuit voltage of the devices, enabling a maximum power conversion efficiency (PCE) of 20.43%, in comparison with PCE of 18.52% for the control device. The authors' findings provide a novel strategy for efficient defect passivation in the perovskite solar cells based on controlling the electronic configuration of passivation molecules.