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.

Key Laboratory of Polar Materials and Devices(MOE)and Department of Electronics,East China Normal University,Shanghai 200241,China;State Key Laboratory of ASIC and System,School of Microelectronics,Fudan University,Shanghai 200433,China

[1]Saichao Yan;Jinchen Wei;Shanshan Wang;Menglin Huang;Yu-Ning Wu;Shiyou Chen-.Defect physics of the quasi-two-dimensional photovoltaic semiconductor GeSe)[J].中国物理B（英文版）,2022(11):67-73

TFSCs,VGe,Sei,Gei

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