Abstract
AbstractSolar fuels are a promising way to store solar energy seasonally. This paper proposes an earth‐abundant heterostructure to split water using a photovoltaic‐electrochemical device (PV‐EC). The heterostructure is based on a hybrid architecture of a thin‐film (TF) silicon tandem on top of a c‐Si wafer (W) heterojunction solar cell (a‐Si:H (TF)/nc‐Si:H (TF)/c‐Si(W)) The multijunction approach allows to reach enough photovoltage for water splitting, while maximizing the spectrum utilization. However, this unique approach also poses challenges, including the design of effective tunneling recombination junctions (TRJ) and the light management of the cell. Regarding the TRJs, the solar cell performance is improved by increasing the n‐layer doping of the middle cell. The light management can be improved by using hydrogenated indium oxide (IOH) as transparent conductive oxide (TCO). Finally, other light management techniques such as substrate texturing or absorber bandgap engineering were applied to enhance the current density. A correlation was observed between improvements in light management by conventional surface texturing and a reduced nc‐Si:H absorber material quality. The final cell developed in this work is a flat structure, using a top absorber layer consisting of a high bandgap a‐Si:H. This triple junction cell achieved a PV efficiency of 10.57%, with a fill factor of 0.60, an open‐circuit voltage of 2.03 V and a short‐circuit current density of 8.65 mA/cm2. When this cell was connected to an IrOx/Pt electrolyser, a stable solar‐to‐hydrogen (STH) efficiency of 8.3% was achieved and maintained for 10 hours.
Highlights
Because of the intermittent solar radiation availability, energy storage is a key factor for the implementation of solar energy
This might be caused by a difference in reflection and absorbance at the cell front surface due to instabilities associated with the quality and thickness of the indium‐doped tin oxide (ITO) deposition
Since the highly doped n‐layer samples show the best fill factor (FF) and open‐circuit voltage (Voc) without a major detrimental effect on the short‐circuit current (Jsc), it is assumed to be the best choice for this tunneling recombination junctions (TRJ), and it would be used further in the triple junction configuration
Summary
Because of the intermittent solar radiation availability, energy storage is a key factor for the implementation of solar energy. A possible approach to achieve the high voltages needed using silicon could be a novel multijunction consisting of a hybrid device that combines wafer (W) and thin‐film (TF) silicon technologies. This concept has already been proven to be able to achieve high open circuit voltages and short circuit current densities in double junctions.[4] In the case of water splitting, an a‐Si:H (TF)/nc‐Si:H (TF)/c‐Si(W) triple junction device has been proposed for solar water splitting, with a potential to achieve solar‐to‐hydrogen (STH) efficiencies[5] of about 9%.
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