Improved efficiency of n-ZnO/p-Si based photovoltaic cells by band offset engineering

Abstract The theoretical approach towards improving the photovoltaic response of n-ZnO/p-Si heterojunctions proposed by Knutsen et al. [Phys. Status Solidi A 210 (2013) 585–588] has been experimentally tested. AZO/n-Zn (1− x ) Mg x O layers were deposited at 160 °C on p-Si substrates by atomic layer deposition (ALD) with magnesium concentration in the 0–4 at% range. The examined devices showed a reduction of the conduction band offset from (0.63±0.03) eV to (0.48±0.03) eV. This decrease leads to a diminishing impact of recombination centers at the interface between zinc oxide based layers and silicon substrate, when the Mg content is below ~1.6 at%. In this range, the overall photovoltaic efficiency increased from ~3.7% to ~6.0%. As a next step, we tested solar cells with similar magnesium concentration in the Zn (1− x ) Mg x O layer, but deposited at 300 °C. Due to the higher deposition temperature, a further 1.1% increase in efficiency has been obtained. So far, this is the highest reported efficiency for a ZnO/Si heterojunction grown by ALD method, thus experimentally confirming the validity of the approache s here studied for raising the efficiency of heterojunctions solar cells based on n-ZnO/p-Si, while significantly reducing the fabrication complexity respect to conventional Si based devices as emphasized by Hussain et al. [Sol. Energy Mater. Sol. Cells 139 (2015) 95–100].