Na-Diffusion Enhanced p-type Conductivity in Cu(In,Ga)Se_2
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- 英文论文题名：Na-Diffusion Enhanced p-type Conductivity in Cu(In,Ga)Se_2
- 论文作者：陈时友 ; 袁振坤 ; 龚新高 ; 魏苏淮
- 年：2017
- 作者机构：华东师范大学极化材料与器件教育部重点实验室;复旦大学计算物质科学教育部重点实验室;北京计算科学研究中心;
- 英文论文关键词：Cu(In ; Ga)Se2 ; Cu2ZnSn(S ; Se)4 ; Na and K doping
- 会议召开时间：2017-05-27
- 会议录名称：第四届新型太阳能电池学术研讨会论文集
- 英文会议录名称：Abstract Book of the 4th Conference on New Generation Solar Cells
- 语种：英文
- 分类号：TM914.42
- 学会代码：ZKYQ
- 会议名称：第四届新型太阳能电池学术研讨会
- 会议地点：中国北京
- 主办单位：中国可再生能源学会光化学专业委员会
- 学会名称：中国科学院物理研究所清洁能源实验室
- 页数：1
- 文件大小：679k
- 原文格式：D
- 会议级别：全国
摘要
Incorporation of Na(K) is now a standard process in the fabrication of the chalcopyrite Cu(In,Ga)Se2(CIGS) and kesterite Cu2ZnSn(S,Se)4(CZTSSe) thin film solar cells and was found very important for achieving high efficiency.It is believed that its beneficial effect results partially from the increase of the hole concentration after Na(K) doping.However, how the Na(K) doping increases the hole concentration is not clear, although this problem has been intensively studied in the past 15 years.To further improve the efficiency of the CIGS solar cells(to over 25%), there is an urgent need to unveil the mechanism of the hole concentration increase in the Na(K) doped CIGS.Using first-principles calculations, we find that the Na dopant is most likely to take place of Cu(forming NaCu) and is electrically inactive in CIGS, so the observed increase of hole concentration can not be understood according to the traditional doping theory.Here we propose a new mechanism.A high concentration of NaCu are formed in CIGS(Na diffuses into the CIGS grains) at a Na-rich and high-temperature growth environment.However, during cooling, the equilibrium concentration(solubility) of Na in the bulk of CIGS becomes lower, and NaCu is not thermodynamically stable any more in the CIGS grains at low temperature, so Na tends to diffuse out of the CIGS grains.Since Na is a fast diffusor in bulk CIGS with a small migration energy, Na can diffuse out of the CIGS grains and leaves the Cu sites unoccupied, then a high concentration of Cu vacancies(VCu) are formed within the grains.The subsequent rinsing in water can further facilitate the formation of VCu.Because the water rinsing can significantly dissolve Na at the CIGS surface and decrease the chemical potential of Na(the environment becomes more and more Na-poor, so the formation energy of Na dopants in CIGS lattice increases), the out-diffusion of Na from the CIGS grain interiors is enhanced.Since the surfaces and grain boundaries of CIGS films are usually Cu-depleted(more Cu poor than in the grains), so less Cu can diffuse back from the surfaces or grain boundaries into the CIGS grains, then a higher concentration of VCu and hole carriers are formed within the grains.Compared to Na, K has a lower solubility in the bulk of CIGS.Besides, after K doping a K-enriched layer is formed on the CIGS surface, which hinders K diffusion out of the CIGS grains, so less VCu can be formed and the increase of the hole concentration is smaller, in good agreement with the experiments.Based on this dopant-diffusion mechanism, we can also understand the p-type conductivity enhancement in Na-doped CZTSSe, and may design new strategies for achieving efficient p-type or n-type bipolar doping in wide-gap semiconductors.
Incorporation of Na(K) is now a standard process in the fabrication of the chalcopyrite Cu(In,Ga)Se2(CIGS) and kesterite Cu2ZnSn(S,Se)4(CZTSSe) thin film solar cells and was found very important for achieving high efficiency.It is believed that its beneficial effect results partially from the increase of the hole concentration after Na(K) doping.However, how the Na(K) doping increases the hole concentration is not clear, although this problem has been intensively studied in the past 15 years.To further improve the efficiency of the CIGS solar cells(to over 25%), there is an urgent need to unveil the mechanism of the hole concentration increase in the Na(K) doped CIGS.Using first-principles calculations, we find that the Na dopant is most likely to take place of Cu(forming NaCu) and is electrically inactive in CIGS, so the observed increase of hole concentration can not be understood according to the traditional doping theory.Here we propose a new mechanism.A high concentration of NaCu are formed in CIGS(Na diffuses into the CIGS grains) at a Na-rich and high-temperature growth environment.However, during cooling, the equilibrium concentration(solubility) of Na in the bulk of CIGS becomes lower, and NaCu is not thermodynamically stable any more in the CIGS grains at low temperature, so Na tends to diffuse out of the CIGS grains.Since Na is a fast diffusor in bulk CIGS with a small migration energy, Na can diffuse out of the CIGS grains and leaves the Cu sites unoccupied, then a high concentration of Cu vacancies(VCu) are formed within the grains.The subsequent rinsing in water can further facilitate the formation of VCu.Because the water rinsing can significantly dissolve Na at the CIGS surface and decrease the chemical potential of Na(the environment becomes more and more Na-poor, so the formation energy of Na dopants in CIGS lattice increases), the out-diffusion of Na from the CIGS grain interiors is enhanced.Since the surfaces and grain boundaries of CIGS films are usually Cu-depleted(more Cu poor than in the grains), so less Cu can diffuse back from the surfaces or grain boundaries into the CIGS grains, then a higher concentration of VCu and hole carriers are formed within the grains.Compared to Na, K has a lower solubility in the bulk of CIGS.Besides, after K doping a K-enriched layer is formed on the CIGS surface, which hinders K diffusion out of the CIGS grains, so less VCu can be formed and the increase of the hole concentration is smaller, in good agreement with the experiments.Based on this dopant-diffusion mechanism, we can also understand the p-type conductivity enhancement in Na-doped CZTSSe, and may design new strategies for achieving efficient p-type or n-type bipolar doping in wide-gap semiconductors.
Incorporation of Na(K) is now a standard process in the fabrication of the chalcopyrite Cu(In,Ga)Se2(CIGS) and kesterite Cu2ZnSn(S,Se)4(CZTSSe) thin film solar cells and was found very important for achieving high efficiency.It is believed that its beneficial effect results partially from the increase of the hole concentration after Na(K) doping.However, how the Na(K) doping increases the hole concentration is not clear, although this problem has been intensively studied in the past 15 years.To further improve the efficiency of the CIGS solar cells(to over 25%), there is an urgent need to unveil the mechanism of the hole concentration increase in the Na(K) doped CIGS.Using first-principles calculations, we find that the Na dopant is most likely to take place of Cu(forming NaCu) and is electrically inactive in CIGS, so the observed increase of hole concentration can not be understood according to the traditional doping theory.Here we propose a new mechanism.A high concentration of NaCu are formed in CIGS(Na diffuses into the CIGS grains) at a Na-rich and high-temperature growth environment.However, during cooling, the equilibrium concentration(solubility) of Na in the bulk of CIGS becomes lower, and NaCu is not thermodynamically stable any more in the CIGS grains at low temperature, so Na tends to diffuse out of the CIGS grains.Since Na is a fast diffusor in bulk CIGS with a small migration energy, Na can diffuse out of the CIGS grains and leaves the Cu sites unoccupied, then a high concentration of Cu vacancies(VCu) are formed within the grains.The subsequent rinsing in water can further facilitate the formation of VCu.Because the water rinsing can significantly dissolve Na at the CIGS surface and decrease the chemical potential of Na(the environment becomes more and more Na-poor, so the formation energy of Na dopants in CIGS lattice increases), the out-diffusion of Na from the CIGS grain interiors is enhanced.Since the surfaces and grain boundaries of CIGS films are usually Cu-depleted(more Cu poor than in the grains), so less Cu can diffuse back from the surfaces or grain boundaries into the CIGS grains, then a higher concentration of VCu and hole carriers are formed within the grains.Compared to Na, K has a lower solubility in the bulk of CIGS.Besides, after K doping a K-enriched layer is formed on the CIGS surface, which hinders K diffusion out of the CIGS grains, so less VCu can be formed and the increase of the hole concentration is smaller, in good agreement with the experiments.Based on this dopant-diffusion mechanism, we can also understand the p-type conductivity enhancement in Na-doped CZTSSe, and may design new strategies for achieving efficient p-type or n-type bipolar doping in wide-gap semiconductors.
引文
[1]Z.-K.Yuan,S.Chen*,Y.Xie,J.S.Park,H.Xiang,X.-G.Gong,and S.-H.Wei,Adv.Energy Mater.,2016,6,1601191.
[2]C.-Y.Liu,Z.-M.Li,H.-Y.Gu,S.-Y.Chen,H.Xiang,X.-G.Gong*,Adv.Energy Mater.2016,1601457.
[2]C.-Y.Liu,Z.-M.Li,H.-Y.Gu,S.-Y.Chen,H.Xiang,X.-G.Gong*,Adv.Energy Mater.2016,1601457.