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

Transition metal oxides (TMOs) have recently been proved to efficiently serve as hole-selective contacts in crystalline silicon (c-Si) heterojunction solar cells. In the present work, two TMO/c-Si heterojunctions are explored using MoO3 (reference) and V2O5 as an alternative candidate. It has been found that V2O5 devices present larger (16% improvement) power conversion efficiency mainly due to their higher open-circuit voltage. While V2O5/c-Si devices with textured front surfaces exhibit larger short-circuit currents, it is also observed that flat solar cell architectures allow for passivation of the V2O5/n-Si interface, giving significant carrier lifetimes of 200 µs (equivalent to a surface recombination velocity of Seff ~140 cm s-1) as derived from impedance analysis. As a consequence, a significant open-circuit voltage of 662 mV is achieved. It is found that, at the TMO/c-Si contact, a TMO work function enhancement ¿FTMO occurs during the heterojunction formation with the consequent dipole layer enlargement ¿’=¿+¿FTMO. Our results provide new insights into the TMO/c-Si contact energetics, carrier transport across the interface and surface recombination allowing for further understanding of the nature of TMO/c-Si heterojunctions.Peer ReviewedPostprint (published version

Bias-free syngas production from solar CO ₂ conversion employing a Cu foam cathode coated with Zn nanoflakes as catalyst and integrated in a scalable solar flow-cell reactor.

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.

Ni/V ₂ O _x stacks applied to an interdigitated back-contacted n-type c-Si solar cell structure are explored, reaching cell efficiencies up to 19.7%.