Laboratory for Photovoltaics, Physics and Materials Science Research Unit , University of Luxembourg , Rue du Brill 41 , L-4422 Belvaux , Luxembourg.
ACS Appl Mater Interfaces. 2018 Aug 29;10(34):28553-28565. doi: 10.1021/acsami.8b08076. Epub 2018 Aug 16.
An accurate determination of the net dopant concentration in photovoltaic absorbers is critical for understanding and optimizing solar cell performance. The complex device structure of multilayered thin-film solar cells poses challenges to determine the dopant concentration. Capacitance-voltage ( C- V) measurements of Cu(In,Ga)Se thin-film solar cells typically yield depth-dependent apparent doping profiles and are not consistent with Hall measurements of bare absorbers. We show that deep defects cannot fully explain these discrepancies. We instead find that the space charge region capacitance follows the model of a linearly graded junction in devices containing a CdS or Zn(O,S) buffer layer, indicating that elemental intermixing at the absorber/buffer interface alters the dopant concentration within the absorber. For absorbers covered with MgF, C- V measurements indeed agree well with Hall measurements. Photoluminescence measurements of Cu(In,Ga)Se absorbers before and after deposition of a CdS layer provide further evidence for a significant reduction of the near-surface net dopant concentration in the presence of CdS. We thus demonstrate that interdiffusion at the absorber/buffer interface is a critical factor to consider in the correct interpretation of doping profiles obtained from C- V analysis in any multilayered solar cell and that the true bulk dopant concentration in thin-film devices might be considerably different.
准确确定光伏吸收体中的净掺杂浓度对于理解和优化太阳能电池性能至关重要。多层薄膜太阳能电池的复杂器件结构给确定掺杂浓度带来了挑战。Cu(In,Ga)Se 薄膜太阳能电池的电容-电压 (C-V) 测量通常会产生深度相关的表观掺杂分布，并且与裸吸收体的霍尔测量不一致。我们表明，深缺陷不能完全解释这些差异。相反，我们发现空间电荷区电容符合含有 CdS 或 Zn(O,S)缓冲层的器件中线性梯度结的模型，这表明在吸收体/缓冲层界面处的元素互混改变了吸收体内的掺杂浓度。对于覆盖有 MgF2 的吸收体，C-V 测量确实与霍尔测量非常吻合。在沉积 CdS 层之前和之后对 Cu(In,Ga)Se 吸收体进行的光致发光测量提供了进一步的证据，表明在 CdS 存在的情况下，近表面净掺杂浓度显著降低。因此，我们证明了在任何多层太阳能电池中，从 C-V 分析获得的掺杂分布的正确解释中，吸收体/缓冲层界面的互扩散是一个关键因素，并且薄膜器件中的真实体掺杂浓度可能会有很大的不同。
