Studies on DC Magnetron Sputtered AZO Thin Films for HIT Solar Cell Application

Abstract

Aluminum doped zinc oxide (AZO) is becoming an important and alternative transparent conducting oxide (TCO) material for solar photovoltaic applications due to its good electrical and optical characteristics, lower cost and more abundance, non-toxicity and stability in hydrogen plasma when compared to the popular indium tin oxide (ITO). In this work, AZO films are deposited on glass and silicon substrates with direct current (DC) magnetron sputtering using 5N pure Zinc Oxide target doped with 2 wt% Al2O3.The effect of deposition conditions on the structural, electrical and optical properties of the AZO films are investigated. The results demonstrated that the measured thickness of the deposited films are in the range 135- 490 nm. The X-ray diffraction studies reveal that the AZO films exhibit hexagaonal-wurtzite structure with the preferred orientation of grains along the (002) planes and an average crystal size of ~42 nm. At optimized sputter deposition parameters of an electrode distance of ~ 60 mm, substrate temperature of ~ 200 °C, target DC power of ~150 W and working pressure of ~2∙10¯³ mbar; the AZO films have shown an electrical resistivity of 1.27∙10¯³ Ω∙cm and an average optical transmittance value of 83.76% in the visible range for an optimal film thickness of ~265 nm. Finally HIT Solar Cells with AZO/p-a-Si:H/i-Si:H/n-c-Si/na-Si:H/Al structure have been fabricated by applying the optimized AZO films as front transparent electrodes. It is observed from the preliminary experiments that the fabricated cells have shown an initial photo conversion efficiency of 10.18% with an open circuit voltage (Voc) of 890 mV, short circuit current density (Jsc) of 15.68 mA/cm2 and a fill factor (FF) of ~ 73%.