Dye‐Controlled Interfacial Electron Transfer for High‐Current Indium Tin Oxide Photocathodes

Abstract

Efficient sensitized photocathodes are highly desired for solar fuels and tandem solar cells, yet the development is hindered by the scarcity of suitable p-type semiconductors. The generation of high cathodic photocurrents by sensitizing a degenerate n-type semiconductor (tin-doped indium oxide; ITO) is reported. The sensitized mesoporous ITO electrodes deliver cathodic photocurrents of up to 5.96±0.19 mA cm(-2), which are close to the highest record in conventional p-type sensitized photocathodes. This is realized by the rational selection of dyes with appropriate energy alignments with ITO. The energy level alignment between the highest occupied molecular orbital of the sensitizer and the conduction band of ITO is crucial for efficient hole injection. Transient absorption spectroscopy studies demonstrate that the cathodic photocurrent results from reduction of the photoexcited sensitizer by free electrons in ITO. Our results reveal a new perspective toward the selection of electrode materials for sensitized photocathodes.

Metal oxide nanoparticles and their applications in nanotechnology

“…Because of the complex structure of crystalline In 2 O 3 , it was thought that the factors that determine the high conductive mechanism and lead to a low resistivity were unclear [176]. Recently, it was found that ITO could both donate and accept electrons in dye-coated ITO films when photoinduced charge transfer occurred [177]. When ITO was modified with elements such as Mg, Ca, Yb, etc., the electrodes maintained their electrical characteristics but increased their ambient stability [178].…”

Kinetic pathway for interfacial electron transfer from a semiconductor to a molecule

“…The acute sensitivity of this reaction to the number of TiO 2 electrons present in the nanocrystallite 17 and the very weak driving-force dependence reported by most [19][20][21][22] , but not all 23 , has led many to conclude that observed rate constants report only on the diffusional encounters of the TiO 2 electrons with the molecular acceptors [24][25][26][27] . Clifford et al found that interfacial electron transfer was most easily understood when the physical location of the acceptor frontier molecular orbitals was taken into account 19 , which has been exploited to optimize interfacial electron transfer with highly doped degenerate semiconductors 28 . Collectively, the prior literature is in line with the viewpoint that electron transfer from a semiconductor to a molecular acceptor is sensitive to distance, which naturally raises the question of whether specific interfacial pathways exist.…”

Computational Approaches to Photoelectrode Design through Molecular Functionalization for Enhanced Photoelectrochemical Water Splitting

“… provide overviews of experimental investigations of photoelectrode/molecular catalyst systems. However, many questions remain about the various factors that affect the efficiency of the photoelectrode/molecular catalyst interface such as band‐edge alignment between the photoelectrode and molecular catalyst and between the molecular catalyst and the electrolyte, stable immobilization of the molecular catalyst to the photoelectrode surface, the absence of deleterious surface states, and facile interfacial charge transfer . Therefore, the systematic experimental search for photoelectrode/molecular catalyst systems for water splitting is still a relatively nascent field, even though there are a few comparative studies of experimental catalytic activities and mechanisms of commonly used molecular catalysts .…”

“…The significant computational cost of first‐principles MD, hybrid functional DFT, and MBPT calculations should prompt efforts to formulate widely applicable design rules or heuristics. This may be accelerated by the availability of experimental measurements on a wide variety of photoelectrode/molecular catalyst systems, allowing easy benchmarking and validation of computational methods.…”

“…The molecular catalyst overlayer may be modeled as a modification of the kinetic rate constant for charge transfer at the semiconductor/liquid interface or as a surface charge trap . This approach would likely need heuristics about the charge‐transfer mechanism between the photoelectrode and molecular catalyst and the catalyst and the electrolyte, which may be obtained from experimental studies of photoelectrode/molecular catalyst systems …”