Tuning the Optical Absorption Property of GeSe Thin Films by Annealing Treatment

As an emerging promising photovoltaic absorber material, GeSe has attracted significant interest recently due to its simple binary composition, attractive optical and electrical properties as well as earth‐abundant and low‐toxic constituents. However, no systematic study on the absorption property tuning of GeSe has been reported. Here, first it is shown that the crystallization temperature of amorphous GeSe is about 330 °C through differential thermal analysis and temperature‐dependent X‐ray diffraction. Next, GeSe films with tunable absorption property in the range of 1.79–1.14 eV are fabricated by annealing amorphous GeSe films at different temperatures. Finally, through the combined analysis of bandgaps measured by transmission spectroscopy and nanosheet thickness characterized by cross‐sectional high‐resolution transmission electron microscopy, the blue shift of bandgap with decreasing thickness of nanosheets has been attributed to the quantum confinement effect. Such continuously tunable absorption property of GeSe films makes it more useful for further optoelectronics.