Criteria for improving the properties of ZnGeAs₂ solar cells

We explore the potential utility of the II-IV-V semiconductor ZnGeAs ₂ as the absorber material in solar cells. As-deposited ZnGeAs ₂ films prepared by pulsed laser deposition are amorphous because of the limited substrate temperature that can be used without the rapid loss of volatile Zn and As. Thermal processing above 450°C results in crystallization and improved electrical properties with hole mobilities as high as 58 cm²/V s. The annealed films were used to fabricate p-type ZnGeAs₂: n-type CdS cells on SnO₂-buffered borosilicate glass substrates in the so-called superstrate geometry. Light-induced currents of up to ~2 mA/cm² and open-circuit voltages of up to 470 mV were observed using backside illumination, indicating that these nascent devices hold potential for realizing high performance solar cells from earth-abundant elements. The performance of the devices fabricated to-date is degraded by conduction through shorts resulting from the presence of micron-sized pinholes in the absorber layer.