Influence of the AlInN thickness on the photovoltaic characteristics of AlInN on Si solar cells deposited by RF sputtering

The influence of the AlInN thickness (65-145 nm) on the photovoltaic characteristics of In-rich n-Al_xIn_1-xN (x ∼0.38-0.42) on p-Si(111) heterojunctions deposited by radio frequency sputtering has been reported. All samples show a closely packed columnar morphology with a root mean-squared surface roughness below 3.7 nm and an apparent optical bandgap energy of ∼2.0 eV. Dark current density-voltage curves of the solar cell devices based on the developed AlInN/Si(111) heterojunction reveal shunt and series resistances in the range of 1.3-5.0 kΩ and 7.7-16.2 Ω depending on the AlInN thickness, respectively. Their photovoltaic performance shows an enhancement with the AlInN thickness, with an increase of the short circuit current and conversion efficiency from 16 to 19 mA cm^-2 and from 1.8 to 2.5% under one-sun AM1.5G illumination. At the same time, the open circuit voltage and the fill factor remain at ∼0.34-0.40 V and ∼30-37%, respectively. These effects are due to the enhanced optical transmittance of the AlInN layer in the wavelength range in which the maximum of the Si spectral photoresponse occurs, in agreement with the increased responsivity of the devices at 950 nm of 450 mA W^-1. These results demonstrate the feasibility of using In-rich AlInN alloys deposited by radio frequency sputtering as n-type layer of AlInN/p-type Si heterojunction solar cells. (copyright 2018 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)