Surface modification of semiconductor photoelectrodes

Abstract

Photoelectrochemical (PEC) cells have emerged as promising devices that afford the direct conversion of solar energy into electric power and/or chemical fuels. Apart from the obvious importance of the bulk properties of semiconductor materials employed as photoelectrodes, the semiconductor-liquid interface has proven to strongly govern surface-related processes, i.e. the stability, charge separation/recombination and catalytic activity. Because of this, numerous surface treatments have been reported in an effort to tailor the physicochemical properties of the semiconductor-liquid interface, and in turn, the overall PEC response. In this Perspective article we provide a brief conceptual overview of these surface engineering treatments, connecting the particular effects on the interfacial energetics with the respective consequences on the performance. The beneficial effects that arise from surface treatment are categorized as (i) the protection of the surface against photocorrosion, (ii) the passivation of deleterious surface states, (iii) the modification of the band edge positions or band bending, and (iv) the selective extraction of carriers and improved catalytic activity. State-of-the-art surface treatments such as the adsorption of organic molecules or ions, the deposition of semiconductor overlayers and metal nanoparticles or etching procedures are exemplified and described with respect to the observed beneficial effects. A common emerging theme from recent work is that one single surface treatment can lead to multiple distinct effects. Overall, we suggest that surface engineering holds the key for effectively managing the intrinsic common defects of native semiconductor photoelectrodes regardless of their nature, leading to improved light harvesting efficiency.

Computational insights into charge transfer across functionalized semiconductor surfaces

“…Surface modification is commonly used in PEC cells [31,32] as well as a variety of additional applications such as electronic devices [16][17][18][19][20][21], data storage [22], chemical sensing [23][24][25], molecular nanopatterning [26], and bioengineering [27][28][29][30]. In PEC applications, chemical attachment of organic molecules is a versatile technique used to enhance the stability of low-gap semiconductors while controlling the physiochemical properties of the surface [33].…”

Dual Protection Layer Strategy to Increase Photoelectrode–Catalyst Interfacial Stability: A Case Study on Black Silicon Photoelectrodes

“…[19][20][21][24][25][26]32] The surface morphology of bSi/TiO 2 /Pt electrodes is further investigated in Figure S3 in the Supporting Information. [19][20][21][24][25][26]32] The surface morphology of bSi/TiO 2 /Pt electrodes is further investigated in Figure S3 in the Supporting Information.…”

“…Compared with planar Si, nanoporous black Si exhibits many attractive properties, such as low reflectance and high surface area. [19][20][21][22][23][24][25][26] However, these efforts lack evidence of stability under electrolysis for more than 12 h and nanoporous black Sibased photocathodes continue to suffer from degradation under prolonged electrolysis (Table S1, Supporting Information). [16][17][18][19] Unfortunately, Sibased photoelectrodes often suffer from poor stability due to spontaneous silicon oxide (SiO 2 ) forma tion upon exposure to air.…”

EFFECT OF pH ON PHOTOVOLTAGE BEHAVIOR OF TIO2 PHOTOANODES

“…According to [18], [19] variation of pH of an electrolyte shift the energy positions of bands of the semiconductor at a rate of 59 meV per unit of pH. All these represent chemical reactions, which are accompanied by the transfer of an electric charge across the interface; this in aftermath allows finely tuning the driving force of the processes occurring in the system [20].…”