Defect physics of the quasi-two-dimensional photovoltaic semiconductor GeSe |
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Affiliation: | 1.Key Laboratory of Polar Materials and Devices(MOE) and Department of Electronics, East China Normal University, Shanghai 200241, China;2.State Key Laboratory of ASIC and System, School of Microelectronics, Fudan University, Shanghai 200433, China |
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Abstract: | GeSe has recently emerged as a photovoltaic absorber material due to its attractive optical and electrical properties as well as earth abundancy and low toxicity. However, the efficiency of GeSe thin-film solar cells (TFSCs) is still low compared to the Shockley-Queisser limit. Point defects are believed to play important roles in the electrical and optical properties of GeSe thin films. Here, we perform first-principles calculations to study the defect characteristics of GeSe. Our results demonstrate that no matter under the Ge-rich or Se-rich condition, the Fermi level is always located near the valence band edge, leading to the p-type conductivity of undoped samples. Under Se-rich condition, the Ge vacancy (VGe) has the lowest formation energy, with a (0/2-) charge-state transition level at 0.22 eV above the valence band edge. The high density (above 1017 cm-3) and shallow level of VGe imply that it is the p-type origin of GeSe. Under Se-rich growth condition, Sei has a low formation energy in the neutral state, but it does not introduce any defect level in the band gap, suggesting that it neither contributes to electrical conductivity nor induces non-radiative recombination. In addition, Gei introduces a deep charge-state transition level, making it a possible recombination center. Therefore, we propose that the Se-rich condition should be adopted to fabricate high-efficiency GeSe solar cells. |
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Keywords: | GeSe bulk point defect concentration photovoltaic |
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