Strain Relaxation and Light Management in Tin-Lead Perovskite Solar Cells to Achieve High Efficiencies

Tin-lead (Sn-Pb)-based perovskite solar cells (PSCs) still exhibit inferior power conversion efficiency (PCE) compared to their pure Pb counterparts because of high voltage loss (V-L) and high photocurrent loss in the infrared region. This study explores that a small amount of cesium ion (Cs+) incorporation in the lattice of Sn-Pb perovskite can reduce the relative lattice strain, which in turn decreases the V-L less than 0.50 V. Moreover, surface and bulk trap densities also seem to be reduced by Cs+ addition, as concluded by thermally stimulated current measurements and increased carrier lifetime by photoluminescence study. It was discovered that a small amount of Cs+ lowered the Urbach energy, which can be used as a signature to optimize the optoelectronic and the photovoltaic properties of multication perovskite materials. This study further demonstrates that a high external quantum efficiency (similar to 80% at 900 nm) can be obtained with fluorine-doped tin oxide (FTO) glass rather than frequently used indium tin oxide (ITO) glass. The strategies employed in the work improved the open-circuit voltage to 0.81 V and gave a photocurrent density of >30 mA/cm(2) and a PCE of >20% using a band gap of 1.27 eV.