Sputtered ZnTe:N and ZnO:Al for Solar Cell Electrodes and Recombination Junctions

Abstract

AbstractWe have used sputtered ZnTe:N and ZnO:Al as transparent electrodes for CdTe based solar cells. ZnTe:N is reactively sputtered with 3% N2 in the sputter gas. The ZnTe:N films typically have transmission near 85% above 750 nm and resistivity as low as 10 ohm-cm with fine grains of approximately 30 nm diameter. ZnO:Al is sputtered from a ZnO:Al2O3 (2%) target. The ZnO:Al films have resistivity as low as 4 × 10-4 ohm-cm with 80-95% transmission over the visible spectrum. To test the stability of the films, ZnTe:N films were annealed in argon, dry air and nitrogen at a range of temperatures from 200°C to 500°C. Annealing decreased the resistivity for temperatures up to 350°C and increased for temperatures greater than 350°C. ZnO:Al films were annealed in dry air at temperatures from 300°C to 550°C. Though the resistivity increased at higher annealing temperatures, there was no change in the transmission. Important to the function of a tandem solar cell is a transparent contact, like ZnTe:N/ZnO:Al, to replace the traditional metal contact to the CdS/CdTe solar cell. We investigate the ZnTe:N/ ZnO:Al bilayer as a possible recombination junction. The rf sputtered ZnTe:N and ZnO:Al films were characterized by AFM, STM, XRD, transmission, 4-point probe, and Hall measurements.