In2Se3, In2Te3, and In2(Se,Te)3 Alloys as Photovoltaic Materials

In its lowest-energy three-dimensional (3D) hexagonal crystal structure (gamma phase), In2Se3 has a direct band gap of similar to 1.8 eV and displays high absorption coefficient, making it a promising semiconductor material for optoelectronics. Incorporation of Te allows for tuning the band gap, adding flexibility to device design and extending the application range. Here we report results of hybrid density functional theory calculations to assess the electronic and optical properties of gamma-In2Se3, gamma-In2Te3, and gamma-In2(Se1-xTex)3 alloys, and initial experiments on the growth and characterization of gamma-In2Se3 thin films. The predicted band gap of 1.84 eV for gamma-In2Se3 is in good agreement with the absorption onset derived from transmission and reflection spectra of thin films. We show that incorporation of Te gives gamma-In2(Se1-xTex)3 alloys with a band gap ranging from 1.84 eV down to 1.23 eV, thus covering the optimal band gap range for single-junction solar cells. In addition, the gamma-In2Se3/gamma-In2(Se1-xTex)3 bilayer could be employed in tandem solar-cell architectures absorbing at Eg approximate to 1.8 eV and at Eg <= 1.4 eV, toward overcoming the similar to 33% efficiency set by the Shockley-Queisser limit for single junction solar cells. We also discuss band gap bowing and mixing enthalpies, aiming at adding gamma-In2Se3, gamma-In2Te3, and gamma-In2(Se1-xTex)3 alloys to the available toolbox of materials for solar cells and other optoelectronic applications.

Automated summary

This study reports the electronic and optical properties of γ-In2Se3 and Te-doped γ-In2(Se1-xTex)3 alloys using hybrid density functional theory calculations and initial experiments on γ-In2Se3 thin film growth and characterization. The experimental results are consistent with the calculated predictions and demonstrate that Te doping can tune the band gap range of the alloys, making them suitable for single-junction solar cells.