Dual-purpose tunnel oxide passivated contact on silicon photoelectrodes with high photovoltages for tandem photoelectrochemical devices enabling unassisted water splitting

Abstract

A tandem photoelectrochemical (PEC) water-splitting device for solar hydrogen production consists of two light absorbers with different bandgaps. It is important to enhance the performance of both cells to achieve...

Monolithically Integrated BiVO4/Si Tandem Devices Enabling Unbiased Photoelectrochemical Water Splitting

“…TTO deposition accounts for the 40 mV difference in photovoltage compared to the value obtained in our earlier study (Pt/Ti/TOPCon Si, 640 mV). [ 10 ] The same structure illuminated with light filtered by a blank BVO (the red curve in Figure S2, Supporting Information) produced an onset potential of 598 mV, which should be the maximum value of photovoltage attainable by TOPCon Si when integrated with BVO. This high photovoltage can be mainly attributed to the insertion of the SiO 2 passivation layer, which decouples the c‐Si absorber from the highly doped poly‐Si charge selective contacts and suppresses Auger‐recombination at the surface of c‐Si.…”

“…[ 11,12 ] The SiO 2 passivating layer also improves the thermal stability by acting as a diffusion barrier, preventing the thermal diffusion of elements from other contacting materials into c‐Si. Our prior study showed the superior thermal stability of TOPCon Si in a temperature range up to 600 °C, [ 10 ] which is sufficient for the high‐temperature processes for SnO 2 and BVO.…”

“…Thanks to recent advances in c-Si photovoltaic (PV) technology, c-Si PEC devices have achieved photovoltages exceeding 0.6 V by introducing a surface passivation layer that reduces surface recombination loss. [8] Wang et al employed a silicon heterojunction with an intrinsic thin-layer (HIT) to passivate the surface of c-Si with hydrogenated amorphous Si (a-Si:H); its HIT photocathode for hydrogen evolution reaction (HER) and photoanode for oxygen evolution reaction (OER) achieved photovoltages of 0.64 V. [9] We also reported a state-of-the-art c-Si photocathode and photoanode based on tunnel-oxide-passivated contact (TOPCon) structure; this structure applies an SiO 2 passivation layer and provides photovoltages of 0.64-0.65 V. [10] Because these surfacepassivated Si photoelectrodes have excellent performance, coupling them with a large bandgap top cell can be a promising way to realize a highly efficient tandem PEC device. [11,12] On the other hand, significant effort is still needed to develop a large bandgap top cell with an appropriate bandgap of ≈1.8 eV, excellent electronic properties, and no use of expensive elements.…”

“…In this work, we applied various novel approaches to enhance the performance of a monolithic tandem device comprised of a BVO top cell and a c-Si bottom cell. To achieve the best performance from a c-Si bottom cell even after high-temperature deposition process (400-500 °C) of BVO/SnO 2 heterojunction and Ta:SnO 2 (TTO) recombination layers, we used a TOPCon Si photoelectrode investigated in our previous study, [10] which was found able to endure high processing temperatures up to 600 °C without losing its high photovoltage of 0.64-0.65 V. This range of photovoltages is among the highest values from any silicon photoelectrodes. Other c-Si cells, such as those with an HIT structure, may provide comparable photovoltage; [9,41] however, they would hardly be applicable to a monolithic tandem PEC because its a-Si:H passivation layer is thermally diffusive and unstable.…”

Metal–insulator–semiconductor photoelectrodes for enhanced photoelectrochemical water splitting

“…Moon et al proposed a passivation solution using a tunnel oxide passivated contact (TOPCon) structure. 327 The ultrathin SiO 2 tunnel layer significantly reduces surface carrier recombination rates, while the doped polycrystalline silicon layer forms an ohmic contact between SiO 2 and the metal, resulting in excellent carrier collection efficiency. Additionally, the SiO 2 layer and polycrystalline silicon layer serve as effective diffusion barrier layers and impurity absorption layers, greatly enhancing the thermal stability of the device during high-temperature fabrication processes and preventing the diffusion of metals into Si.…”