This work reports on a comparative study comprising three transition metal oxides, MoO3, WO3 and V2O5, acting as front p-type contacts for n-type crystalline silicon heterojunction solar cells. Owing to their high work functions (>5 eV) and wide energy band gaps, these oxides act as transparent hole-selective contacts with semiconductive properties that are determined by oxygen-vacancy defects (MoO3-x), as confirmed by X-ray photoelectron spectroscopy. In the fabricated hybrid structures, 15 nm thick transition metal oxide layers were deposited by vacuum thermal evaporation. Of all three devices, the V2O5/n-silicon heterojunction performed the best with a conversion efficiency of 15.7% and an open-circuit voltage of 606 mV, followed by MoO3 (13.6%) and WO3 (12.5%). These results bring into view a new silicon heterojunction solar cell concept with advantages such as the absence of toxic dopant gases and a simplified low-temperature fabrication process.Preprin

During the last decade, transition metal oxides have been actively investigated as hole- and electron-selective materials in organic electronics due to their low-cost processing. In this study, four transition metal oxides (V₂O₅, MoO₃, WO₃, and ReO₃) with high work functions (>5 eV) were thermally evaporated as front p-type contacts in planar n-type crystalline silicon heterojunction solar cells. The concentration of oxygen vacancies in MoO_3−x was found to be dependent on film thickness and redox conditions, as determined by X-ray Photoelectron Spectroscopy. Transfer length method measurements of oxide films deposited on glass yielded high sheet resistances (~10⁹ Ω/sq), although lower values (~10⁴ Ω/sq) were measured for oxides deposited on silicon, indicating the presence of an inversion (hole rich) layer. Of the four oxide/silicon solar cells, ReO₃ was found to be unstable upon air exposure, while V₂O₅ achieved the highest open-circuit voltage (593 mV) and conversion efficiency (12.7%), followed by MoO₃ (581 mV, 12.6%) and WO₃ (570 mV, 11.8%). A short-circuit current gain of ~0.5 mA/cm² was obtained when compared to a reference amorphous silicon contact, as expected from a wider energy bandgap. Overall, these results support the viability of a simplified solar cell design, processed at low temperature and without dopants.

Electronic properties of Au/V₂O₅/n-Si Schottky device have been investigated by temperature dependent current–voltage (I–V) and capacitance–voltage (C–V) measurements ranging from 300 K to 150 K. Ideality factor (n) and barrier height (ϕ) for the Schottky device were obtained from I–V characteristics as 2.04 and 0.83 eV at 300 K and 6.95 and 0.39 eV at 150 K respectively. It was observed that in presence of inhomogeneity at metal–semiconductor interface, the ideality factor increases and barrier height decreases with the decrease of temperature. The Richardson constant value was estimated as 137 A–cm⁻²–K⁻² from modified Richardson plot, which is closer to the known theoretical value of n-Si where mean value of barrier height $\left(\overline{{\mathrm{\varphi }}_{b0}}\right)$ , and its standard deviation (σ₀) were estimated using double Gaussian distribution (DGD) analysis. Different device parameters, namely, built-in potential, carrier concentration, image force lowering and depletion width were also obtained from the C–V–T measurements. First time use of V₂O₅ thin-film as an interfacial layer (IL) on Au/V₂O₅/n-Si Schottky diode was successfully explained by the thermionic emission (TE) theory. The interesting result obtained in this present work is the V₂O₅ thin-film reduced its conducting capability with decreasing temperature, while it shows a totally insulating behaviour below 150 K.