Advancing CO2-to-Fuel Conversion: Synthesizing Tellurium-Based Semiconductors

Converting CO₂ into energy-dense liquid fuels through the use of renewable energy sources is considered as an important component of addressing ongoing and future energy crises. The most elegant method for this conversion is the photoelectrochemical (PEC) reduction of CO₂, but the key challenge in realizing this process effectively lies in the development of highly efficient photoelectrode materials. In particular, operationally stable p-type photocathodes that can provide electrons to facilitate the required CO₂ reduction processes are required.<br/><br/>In this study, we synthesized new semiconductor thin film absorber material, Zn_x(GaTe₂)_y, via combinatorial sputtering approaches. The material was prepared using a 2-step process wherein room-temperature growth was followed with flash lamp annealing from 300 °C – 550 °C. Our X-ray diffraction study shows that Zn_x(GaTe₂)_y goes through a phase transition from cubic (F-43m) to tetragonal (I-42m) upon increasing Ga content, indicating a nearly complete ordering of atoms and vacancies on the zincblende lattice. Upon changing the cation ratio, a new peak observed in the X-ray diffraction pattern at an angle of ~35° with cubic structured Zn_x(GaTe₂)_y alloy, suggesting an intermediate amount of order can be achieved. At an optimal ratio of Zn:Ga:Te, Raman scattering reveals longitudinal optical (LO) peaks up to the third order when excited with a wavelength of 532 nm and displays superior photo luminescent properties, suggesting its potential to enhance CO₂ reduction capabilities. In the room temperature photoluminescence (PL) spectra, a defect emission is observed at 1.6 eV for all ratio of Zn_x(GaTe₂)_y. Time-resolved photoluminescence (TRPL) data indicates a shift in lifetime during the transition from an ordered to a disordered state.