Approach toward high efficiency CdTe/CdS heterojunction solar cells
Approach toward high efficiency CdTe/CdS heterojunction solar cells
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DOI：
10.1016/0254-0584(95)01626-6
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发表时间：
1996-02-01
影响因子：
4.6
通讯作者：
Levi, DH
中科院分区：
文献类型：
--
作者：
Chou, HC;Rohatgi, A;Levi, DH
通过在CdS/SnO 2/玻璃衬底上沉积不同Te：Cd摩尔比的MOCVD生长CdTe薄膜制备了CdTe太阳电池。在富Te环境中生长的电池显示在CdS/CdTe界面处的原子相互扩散增加，并且产生具有780 mV的开路电压（V-oc）的高效率电池（11.9%）。富镉细胞的效率< 6%。载流子输运分析表明，在富镉电池的隧道/界面复合开关耗尽区复合限制运输富碲电池的传输机制。这表明增强的相互扩散对这些电池是有益的，并导致晶格失配减少或从CdS逐渐过渡到CdTe，具有更少的界面态。为了理解与多晶CdTe电池中的晶界相关的损耗机制，尝试使用外延剥离（ELO）工艺制造薄膜CdTe/CdS器件结构。单晶CdTe和CdTe/CdS外延层通过选择性蚀刻从GaAs衬底分离，然后转移并结合到SnO 2/玻璃衬底。西姆斯分析的CdTe/CdS电池，与Au/Cu欧姆接触的CdTe，表明少得多的铜扩散的单晶CdTe薄膜，由于没有晶界。X射线衍射测量结果表明，CdTe/CdS的晶格结构和质量不发生明显的变化后，剥离过程。开发了一种新的方法，使用XRD和剥离技术，以评估在异质结界面处的晶格失配引起的应变和缺陷。在与GaAs的界面处的CdTe的晶格常数为6.317埃，其小于CdTe块体的理想晶格常数6.481埃。
CdTe solar cells were fabricated by depositing MOCVD grown CdTe films on CdS/SnO2/glass substrates with varying Te:Cd mole ratios in the growth ambient. Cells grown in Te-rich ambient showed increased atomic interdiffusion at the CdS/CdTe interface and produced high-efficiency cells (11.9%) with an open-circuit voltage (V-oc) of 780 mV. Cd-rich cells were < 6% efficient. Carrier transport analysis showed that the transport mechanism switches from tunneling/interface recombination in the Cd-rich cells to depletion region recombination limited transport in the Te-rich cells. This suggests that the enhanced interdiffusion is beneficial for these cells and leads to reduced lattice mismatch or gradual transition from CdS to CdTe with fewer interface states. In order to understand the loss mechanisms associated with grain boundaries in polycrystalline CdTe cells, an attempt was made to fabricate thin film CdTe/CdS device structures using an epitaxial lift-off (ELO) process. Single crystal CdTe and CdTe/CdS epitaxial layers were separated from the GaAs substrate by selective etching and were then transferred and bonded to a SnO2/glass substrate. SIMS analysis of CdTe/CdS cells, with Au/Cu ohmic contacts to CdTe, showed much less Cu diffusion in the single crystal CdTe films due to the absence of grain boundaries. X-ray diffraction measurements showed that the CdTe/CdS lattice structure and quality does not change appreciably after the lift-off process. A new methodology was developed, using XRD and the lift-off technique, to assess the lattice mismatch induced strain and defects at the heterojunction interface. The lattice constant of CdTe at the interface with GaAs was 6.317 Angstrom, which is smaller than the ideal lattice constant of 6.481 Angstrom for the CdTe bulk.