The n‐Silicon/Thallium(III) Oxide Heterojunction Photoelectrochemical Solar Cell

Thallium(III) oxide is a degenerate n‐type semiconductor which can be electrochemically or photoelectrochemically deposited on conducting or semiconducting substrates. The material is highly conductive, transparent, and electrocatalytic. A photoelectrochemical cell consisting of the n‐silicon/thallium(III) oxide photoanode and a platinum cathode in an alkaline solution of the ferrocyanide/ferricyanide redox couple produced a 0.512V open‐circuit photovoltage, 33.5 mA/cm 2 short‐circuit photocurrent density, 0.643 fill factor, and 13.8% photovoltaic efficiency with 80 mW/cm 2 iR‐filtered xenon light. The efficiency was 11.0% with 75.3 mW/cm 2 natural sunlight, and 22.3% with 800 nm monochromatic light. The short‐circuit quantum efficiency at 800 nm was 97%. A xenon photovoltaic efficiency of 10.2% was observed with cast multicrystalline n‐silicon. Photocurrent‐voltage curves were computer simulated using values of the barrier height (0.96V), diode quality factor (1.2), and series resistance (200Ω) that were measured from dark current voltage and capacitance‐voltage curves. A solid‐state photovoltaic cell was fabricated by making a low‐pressure point contact to the front surface of a dry photoanode. The photovoltaic characteristics of the solid‐state cell were nearly identical with those of the photoelectrochemical cell. These results suggest that the photoelectrochemical cell functions like a Schottky‐barrier or SIS solid‐state photovoltaic cell in series with a highly reversible electrochemical cell.