Innovative Wide-Spectrum Mg and Ga-Codoped ZnO Transparent Conductive Films Grown via Reactive Plasma Deposition for Si Heterojunction Solar Cells
Zhongxin Zhou, Yunlong Zhang, Xinliang Chen, Shengzhe Li, Ying Zhao, Xiaodan Zhang
Abstract
In this work, wide-spectrum Mg and Ga-codoped ZnO (MGZO) transparent conductive films are developed via a reactive plasma deposition (RPD) technique with a soft thin-film growth process. MGZO film with a work function of ∼4.36 eV can be achieved within 12 min without any intentional substrate-heating treatment. The 480 nm-thickness MGZO film exhibits a low resistivity of ∼9.9 × 10–4 Ω cm and a high transmittance of ∼82.6% in the UV–vis–NIR region (λ approximately 400 nm–1200 nm). XRD spectra show that MGZO films exhibit (103) preferred orientation as the film thickness increases. A silicon heterojunction (SHJ) solar cell based on 480 nm-thick MGZO at the front side is completed. Excellent continuity of the MGZO film is proven by the cross-sectional SEM images, and there are no cracks and pinholes on the top or bottom of the c-Si pyramids. Further efficiency improvements are achieved using an ultrathin SnOx buffer layer with an ameliorated p-a-Si:H/TCO interface. Also, a silicon heterojunction (SHJ) solar cell using MGZO films on both sides is achieved with a conversion efficiency of 19.02%. These experimental results demonstrate that low-cost RPD-grown MGZO TCO materials could be commercially appropriate replacements for the conventional In2O3-based materials commonly used in SHJ solar cells and other optoelectronic devices.