Impact of target power on the properties of sputtered intrinsic zinc oxide (i-ZnO) thin films and its thickness dependence performance on CISe solar cells

Highly resistive intrinsic zinc oxide (i-ZnO) thin films were deposited via radio frequency (RF) magnetron sputtering with varying the target power (80 W–140 W) at constant sputtering gas pressure (10 mTorr), and the structural, morphological, and optical properties were investigated. The i-ZnO thin film crystallized in Wurtzite hexagonal with a preferential orientation along (002) reflection plane. The variation in morphology from partitioned nano-walls to spherical grains pursued the impact of target power on the growth mechanism of i-ZnO thin films. The optical band gap was increased from 3.16 eV (80 W) to 3.28 eV (120 W) with increasing target power. Additionally, CuInSe2 (CISe) solar cells were fabricated from modified sequentially evaporated metallic precursors by adopting different thicknesses of i-ZnO ranges from 40 nm to 120 nm. The formation of smooth and densely packed grains pursued the effective intermediate layer for the elemental interdiffusion from adjacent layers and protected against the shunt path. 80 nm was the optimum thickness of the i-ZnO film, which yielded 9.23% of conversion efficiency. A further increase of thickness from 80 nm reduced the photovoltaic performance, especially fill factor and elevated value of series resistance. These results explore experimentally the correlation between the i-ZnO thickness and its photovoltaic performance.