Photoelectrochemical (PEC) hydrogen production by utilizing solar energy has been considered as an ideal and renewable pathway for the energy crisis. However, the large band gap of semiconductors severely limit the available sunlight that can be harvested — typically in ultraviolet and visible region with wavelength below 700 nm. Extending light absorption into the infrared region can promote the efficiency of these devices towards the Shockley-Queisser efficiency limit.

Although the Narrow bandgap (NBG) semiconductor are an ideal platform for high-efficiency  NIR-active photoelectrodes, it is difficult to improve the incident photon-to-current conversion efficiency (IPCE) efficiency of NIR-active photoanodes due to the electron-phonon interactions and non-radiative recombination at defects. 

Recently, Prof. YU Shuhong from University of Science and Technology of China of the Chinese Academy of Sciences and the collaborators prepared an efficient NIR-active photoanode by engineering a BiSeTe ternary alloy in the form of lattice-matched morphological heterojunctions (BST-MHs). This BST-MHs photoanode could utilize near-infrared (NIR) light more efficiently and enhance the energy conversion efficiency of photoanodes. Result was published in Nature Communications.

The researchers first grew epitaxial thin nanosheets onto nanotubes to absorb NIR radiation up to 1100 nm. Lattice-matched morphological heterojunctions reduce carrier-trapping interfacial defects arising from the mismatch between two distinct semiconductors.  

They then confirmed the existence of a lattice-matched type-II heterojunction and the ultrafast charge transfer process which enhances electron-hole separation.  

The IPCE of BST-MH photoanode is 36% at 800 nm and the photocurrent density is 3.7 mA·cm^-2 at 0.75 V_RHE under NIR light in an electrolyte solution containing hole scavengers. 

This study established NIR-MHs as a class of new photoanode materials with a wide light-harvesting spectral range and efficient charge separation, which offers new possibilities for the design of efficient NIR-active PEC devices by integrating the advantages of NBG semiconductors into a lattice-matched morphological heterojunction configuration.