Silver-Doped Cu2SnS3Absorber Layers for Solar Cells Application

The p-type semiconductor Cu2SnS3 is alloyed with Ag to investigate its effect on absorber layer and solar cell properties. Ag replaces the Cu in (Cu1‐ x Ag x )2SnS3 (ACTS) up to x ≤ 6% at 550 °C. Above this percentage, Ag forms secondary phases. We find a significant increase in grain size, from hundreds of nanometers to several microns, and increased photoluminescence yield with increasing Ag concentration. Low-temperature photoluminescence measurements show that compensation is increased for the ACTS absorber layers, which could be beneficial for CTS, but also that the electrostatic band gap fluctuations are increased. The external quantum efficiency of the solar cells made from ACTS shows an increased carrier collection length from 320 nm for CTS to 700 nm and a thicker buffer layer. We attribute the increase in collection length to both increased depletion width (increased compensation) and diffusion length (larger grains). Overall the ACTS solar cells have a lower power conversion efficiency due to lower shunt resistance and open-circuit voltage, which are attributed to increase in pinholes, electrostatic fluctuation, and changes at the CdS/ACTS interface.