Optimization of Si doping in ZnO thin films and fabrication of n-ZnO:Si/p-Si heterojunction solar cells

Si acts as efficient dopant of ZnO by providing two free-electrons to the conduction band via its Si4+ ionized state and ZnO:Si thin-films might perform as appropriate transparent-conducting-oxide (TCO) material for Si-based devices. Through optimum-doping of ZnO by similar to 1.53 at.% Si at substrate-temperature (T-S) similar to 150 degrees C, the electrical resistivity (rho) in ZnO:Si films reduced significantly to similar to 5.01 x 10(-3) Omega cm via increased concentration (n(e) similar to 0.65 x 10(20) cm(-3)) and elevated mobility (mu similar to 19.11 V-1 cm(2)s(-1)) of charge-carriers. On further increased doping, electronic configuration of dopants gradually changed from Si-4(+) to Si(4-n)+ (n = 1,2,3) ionized-states that could not generate equivalent charge-carriers and gradually reduced the carrier-concentration and drastically diminished the carrier-mobility. The optical band-gap (E-g) of ZnO:Si films widened spontaneously to similar to 3.588 eV via increased carrier-density, following Burstein-Moss relation. Above 80% visible transmission sharply reduced via resonance near-infrared-absorption at plasma wavelength corresponding to the increased density of doping-elicited charge-carriers. Significantly high 'Figure-of-Merit' (Phi(TC)) of the TCO characteristics similar to 4.15 x 10(-3) Omega(-1) was attained for ZnO:Si films grown via single-step processing at low T-S (150 degrees C), using RF magnetron-sputtering. The fabrication of n-ZnO:Si/p-Si heterojunction solar cells are being reported for the first-time with the major device characteristics adequately correlated to prime optoelectronic properties. (C) 2020 Elsevier B.V. All rights reserved.