Stabilizing inorganic photoelectrodes for efficient solar-to-chemical energy conversion

An efficient, inexpensive and stable photosynthetic material system that absorbs sunlight and uses the absorbed energy to electrochemically produce chemical and fuel products including hydrogen requires photoelectrode assemblies that are stable in electrolytes. Here we report a photoelectrochemical/photosynthetic cell based on inorganic semiconductor photoelectrodes that shows the long-term operational stability necessary for the production of solar fuels and chemicals. The cell's stability is achieved by forming an active device using an inexpensive spin casted (20 nm) transparent conducting polymer coating (poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS)). PEDOT: PSS protects the photoelectrodes from photoelectrochemical corrosion and functionally serve as either a Schottky contact or as an efficient hole transport layer depending upon the choice and design of the underlying semiconductor heterostructure. Coated semiconductors were assessed both as photoelectrochemical and as freestanding, autonomous photosynthetic units and found to be stable for over 12 hours (for wired configuration) in corrosive electrolytes. The solar-to-chemical conversion efficiencies match or exceed devices with more expensive metal-based coatings. Furthermore, the PEDOT: PSS was found to have high electrocatalytic activity, thus no additional electrocatalyst was required. The results suggest a pathway to large scale, inexpensive, hybrid organic-inorganic solar-to-chemical energy conversion systems.