Elimination of trap density by NH 4 Cl passivation for high-performance perovskite solar cells

Different concentrations of NH 4 Cl are introduced to MAPbI 3 precursor solution, planar MAPbI 3 perovskite films, and solar cells’ performance with or without NH 4 Cl have been studied. The NH 4 Cl/MAPbI 3 films exhibit increased grain size and narrowed grain boundaries. The light absorption of perovskite films with different concentrations of NH 4 Cl was also evaluated. To understand the growth of perovskite films with NH 4 Cl added to perovskite precursor solutions, XRD and XPS spectroscopy were conducted on different perovskite film samples. By adding NH 4 Cl, the MAPbI 3 film shows good crystal quality and the shift of Pb peaks indicates that NH 4 Cl is not physically mixed but chemically incorporated into MAPbI 3 films. We attribute the effect to Cl ions of NH 4 Cl combining with free lead ions of MAPbI 3 so as to fill the vacancy of volatile I ions in the NH 4 Cl–MAPbI 3 films. The 20 mg NH 4 Cl-based device showed an enhanced performance of a PCE of 13.67% compared to the device without adding NH 4 Cl with a PCE of 10.24%. The introduction of 20 mg NH 4 Cl achieved the best passivation effect. Using a 20 mg NH 4 Cl device, the trap density can be reduced to 0.84 × 10 16 cm −3 , resulting in more efficient charge removal from the surface and improved performance.