Sputtered Ultrathin TiO2 as Electron Transport Layer in Silicon Heterojunction Solar Cell Technology

Abstract

This work presents the implementation of ultrathin TiO2 films, deposited at room temperature

by radio-frequency magnetron sputtering, as electron-selective contacts in silicon heterojunction

solar cells. The effect of the working pressure on the properties of the TiO2 layers and its subsequent

impact on the main parameters of the device are studied. The material characterization revealed

an amorphous structure regardless of the working pressure; a rougher surface; and a blue shift in

bandgap in the TiO2 layer deposited at the highest-pressure value of 0.89 Pa. When incorporated

as part of the passivated full-area electron contact in silicon heterojunction solar cell, the chemical

passivation provided by the intrinsic a-Si:H rapidly deteriorates upon the sputtering of the ultra-thin

TiO2 films, although a short anneal is shown to restore much of the passivation lost. The deposition

pressure and film thicknesses proved to be critical for the efficiency of the devices. The film

thicknesses below 2 nm are necessary to reach open-circuit values above 660 mV, regardless of the

deposition pressure. More so, the fill-factor showed a strong dependence on deposition pressure,

with the best values obtained for the highest deposition pressure, which we correlated to the porosity

of the films. Overall, these results show the potential to fabricate silicon solar cells with a simple

implementation of electron-selective TiO2 contact deposited by magnetron sputtering. These results

show the potential to fabricate silicon solar cells with a simple implementation of electron-selective

TiO2 contact.