EN11.04.02 : >10% Solar-to-Hydrogen Efficiency Unassisted Water Splitting with ALD Protected Silicon Solar Cells

5:00 PM–7:00 PM Apr 3, 2018 (America - Denver)

PCC North, 300 Level, Exhibit Hall C-E

Chor Seng Tan1 Kyle Kemp1 Chris Chidsey1 Paul McIntyre1

1, Stanford University, Stanford, California, United States

Solar driven photoelectrochemical water splitting is a promising method to directly convert renewable, abundant solar energy into hydrogen fuel. For this technology to be commercially viable, devices for water splitting must be efficient, cheap, and stable. Most of the top-performing devices for unassisted water splitting, however, utilize expensive III-V materials such as InGaP2 and GaAs as the absorber material, thus limiting their scalability. Additionally, most efficient semiconductor absorbers exhibit instability under water splitting conditions, leading many to employ a separated photovoltaic + electrolyzer system design which may incur higher balance of systems costs. We present an efficient, integrated solar water splitting device using silicon-only photovoltaic junctions. By connecting three silicon Heterojunction with Intrinsic Thin layer (HIT) solar cells in series and using an atomic layer deposited (ALD) TiO2 protection layer, we are able to demonstrate unassisted water splitting with over 10% solar-to-hydrogen efficiency in both concentrated acid and base electrolyte under one sun illumination. Enhanced (>60h) chemical stability is achieved by incorporating the ALD-TiO2 layer in these compact, integrated devices. The TiO2 is able to protect the underlying HIT cell because of its excellent stability over a range of pH and potentials, and does not limit the efficiency of the HIT cell due to good band alignment with the conduction band of silicon. The device design, in which the illumination occurs on the side of the solar cell opposite the electrochemical reaction, avoids both parasitic losses due to light absorption and reflection and the instability of silicon at anodic potentials. We use electron beam deposited Pt as the HER catalyst. Iridium oxide or NiFe prepared by chemical solution deposition or by electrodeposition, respectively, act as the OER catalyst. These layers are deposited on porous Ti or Ni substrates, achieving an OER overpotential of 270 mV at 10 mAcm-2.