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

An improved equivalent circuit for hydrogenated amorphous silicon (a-Si:H) solar cells and modules is presented. It is based on the classic combination of a diode with an exponential current-voltage characteristic, of a photocurrent source plus a new term representing additional recombination losses in the i-layer of the device. This model/equivalent circuit matches the I(V) curves of a-Si:H cells over an illumination range of six orders of magnitude. The model clearly separates effects related to the technology of the device (series and parallel resistance) and effects related to the physics of the p-i-n junction (recombination losses). It also allows an effective /spl mu//spl tau/ product in the i-layer of the device to be determined, characterizing its state of degradation.

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.