Zn sub 3 P sub 2 as a New Low Cost High Efficiency Solar Cell Material. Second Quarterly Report, December 1, 1978-February 28, 1979

摘要

Developmental work has been performed on both the isostructural, n-(Cd/sub x/Zn/sub 1-x/) sub 3 P sub 2 /p-Zn sub 3 P sub 2 and non-isostructural, ZnS/Zn sub 3 P sub 2 heterojunction devices. Development of the isostructural alloy devices consisted of the fabrication, testing and analysis of epitaxial n-Cd sub 3 P sub 2 /p-Zn sub 3 P sub 2 devices and the experimental assessment of several methods for the vapor growth of alloy crystals. Analysis of the I-V characteristics of the Cd sub 3 P sub 2 /Zn sub 3 P sub 2 devices indicate a diffusion voltage which varies from 0.445 eV at 212 exp 0 K to 0.22 eV at 86 exp 0 K. The decrease in diffusion voltage on the temperature is consistent with the gradual increase in the distance of the Fermi level from the valence band in Zn sub 3 P sub 2 as carrier freeze-out occurs. The diode factor A also increases to 2.5 over the same temperature range indicating the increased role of interface over bulk recombination at the lower temperature. The value of 0.445 eV obtained for the Cd sub 3 P sub 2 /Zn sub 3 P sub 2 structure compares favorably with a simple band model of the device and indicates that heterojunctions of the alloy should yield devices with sufficiently large diffusion voltage and open circuit voltage to provide useful photovoltaic devices. ZnS/Zn sub 3 P sub 2 heterojunctions with ZnS resistivities between 10 exp 8 -1 omega -cm were fabricated and tested. The I-V characteristics were poor and were dominated by the series resistance of the Zn sub 3 P sub 2 . Analysis of the devices indicate a diffusion voltage of 0.67 eV, but few devices showed any photovoltaic effect. (ERA citation 06:008773)