Weiss Thomas Paul, Carron Romain, Wolter Max H, Löckinger Johannes, Avancini Enrico, Siebentritt Susanne, Buecheler Stephan, Tiwari Ayodhya N
Laboratory for Thin Films and Photovoltaics, Empa - Swiss Federal Laboratories for Materials Science and Technology, Dübendorf, Switzerland.
Laboratory for Photovoltaics, Physics and Materials Science Research Unit, University of Luxembourg, Belvaux, Luxembourg.
Sci Technol Adv Mater. 2019 Apr 9;20(1):313-323. doi: 10.1080/14686996.2019.1586583. eCollection 2019.
Time-resolved photoluminescence (TRPL) is applied to determine an effective lifetime of minority charge carriers in semiconductors. Such effective lifetimes include recombination channels in the bulk as well as at the surfaces and interfaces of the device. In the case of Cu(In,Ga)Se absorbers used for solar cell applications, trapping of minority carriers has also been reported to impact the effective minority carrier lifetime. Trapping can be indicated by an increased temperature dependence of the experimentally determined photoluminescence decay time when compared to the temperature dependence of Shockley-Read-Hall (SRH) recombination alone and can lead to an overestimation of the minority carrier lifetime. Here, it is shown by technology computer-aided design (TCAD) simulations and by experiment that the intentional double-graded bandgap profile of high efficiency Cu(In,Ga)Se absorbers causes a temperature dependence of the PL decay time similar to trapping in case of a recombinative front surface. It is demonstrated that a passivated front surface results in a temperature dependence of the decay time that can be explained without minority carrier trapping and thus enables the assessment of the absorber quality by means of the minority carrier lifetime. Comparison with the absolute PL yield and the quasi-Fermi-level splitting (QFLS) corroborate the conclusion that the measured decay time corresponds to the bulk minority carrier lifetime of 250 ns for the double-graded CIGS absorber under investigation.
时间分辨光致发光（TRPL）被用于确定半导体中少数载流子的有效寿命。这种有效寿命包括体内以及器件表面和界面处的复合通道。在用于太阳能电池应用的Cu(In,Ga)Se吸收体的情况下，据报道少数载流子的俘获也会影响少数载流子的有效寿命。与仅由肖克利-里德-霍尔（SRH）复合的温度依赖性相比，实验测定的光致发光衰减时间的温度依赖性增加可表明俘获的存在，并且这可能导致少数载流子寿命的高估。在此，通过技术计算机辅助设计（TCAD）模拟和实验表明，高效Cu(In,Ga)Se吸收体的有意双梯度带隙分布导致PL衰减时间的温度依赖性类似于复合性前表面情况下的俘获。结果表明，钝化的前表面导致衰减时间的温度依赖性，这可以在没有少数载流子俘获的情况下得到解释，因此能够通过少数载流子寿命来评估吸收体的质量。与绝对PL产率和准费米能级分裂（QFLS）的比较证实了以下结论：对于所研究的双梯度CIGS吸收体，测量的衰减时间对应于250 ns的体内少数载流子寿命。
