1. Photoelectrochemical Systems

Overview

A photoelectrochemical (PEC) cell converts sunlight directly into chemical bonds, and the photoelectrode is where that conversion happens.

A photoelectrode is a layered structure built around a light absorbing semiconductor. Absorbed photons generate electron and hole pairs, a built in field separates them, and a catalyst layer on the surface transfers them to the reactant. Each layer carries its own requirement, from how much of the solar spectrum the absorber uses to how well the catalyst interface steers the reaction, and all of them have to hold at once in contact with electrolyte.

PEC Systems

A PEC system is classified by the sign of the carriers that reach the electrolyte. In a photoanode, photogenerated holes drive an oxidation reaction at the surface while electrons leave through the back contact. In a photocathode, electrons drive a reduction reaction instead. The choice follows from the doping type of the absorber and the direction of band bending at its junctions.

Either electrode is built as a stack. An ohmic contact layer collects the majority carriers at the back. A light absorption layer, the photoabsorber, converts photons into electron and hole pairs. A passivation layer or interlayer protects the absorber from the electrolyte and steers the minority carriers toward the surface. A catalyst layer then transfers them to the reactant.

This stack spans two disciplines. Semiconductor engineering sets how much light is absorbed and how well the carriers are separated and transported. Electrochemical engineering sets the rate and the selectivity of the reaction at the catalyst and electrolyte interface. We work on both, and on the interlayer that has to satisfy the two at once.

Photoabsorber Materials

Metal oxide semiconductors

Oxides are chemically robust in aqueous electrolytes but often show poor carrier transport. We grow epitaxial films by pulsed laser deposition to control crystallographic orientation, strain, and defect chemistry, and to build heterostructures that steer carrier separation. Orientation controlled BiVO₄ and ferroelectric BiFeO₃ layers are representative examples.

Halide perovskites

Halide perovskites offer long carrier diffusion lengths and tunable band gaps, but they decompose on contact with water. We combine charge selective contacts with encapsulation so that these absorbers can operate in aqueous and even seawater environments.

Organic semiconductors

Bulk heterojunction organic semiconductors absorb visible light strongly, and molecular design tunes their energy levels. This flexibility lets us match a photoelectrode to reactions that require mild conditions, such as oxidation in near neutral electrolyte.

Silicon and chalcogenides

Narrow band gap absorbers capture a wide portion of the solar spectrum and suit tandem configurations. We pair them with protective oxide layers and catalyst overlayers to keep the buried junction stable under operation.

Cathodic Reactions: Hydrogen Evolution (HER), Nitrate Reduction (NO₃RR)

Anodic Reactions: Oxygen Evolution (OER), Biomass Valorization (GOR, Lignin Oxidation)

Selected Publications

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