Evolution and role of vacancy clusters at grain boundaries of ZnO:Al during accelerated degradation of Cu(In,Ga)Se2 solar cells revealed by positron annihilation
| Autor: | Christoph Hugenschmidt, Wenqin Shi, Ekkes Brück, Miro Zeman, Marcel Dickmann, Stephan W. H. Eijt, Stefan J. van der Sar, H. Schut, Mirjam Theelen, Andrea Illiberi, Werner Egger, Maik Butterling, Nicolas Barreau |
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| Rok vydání: | 2018 |
| Předmět: |
Materials science
Physics and Astronomy (miscellaneous) 02 engineering and technology 021001 nanoscience & nanotechnology 01 natural sciences Copper indium gallium selenide solar cells Positron annihilation spectroscopy Condensed Matter::Materials Science Positron Chemical physics Vacancy defect 0103 physical sciences General Materials Science Grain boundary Charge carrier Thin film 010306 general physics 0210 nano-technology Transparent conducting film |
| Zdroj: | Physical Review Materials. 2 |
| ISSN: | 2475-9953 |
| Popis: | Positron annihilation lifetime spectroscopy (PALS) and Doppler broadening positron annihilation spectroscopy DB-PAS) depth profiling demonstrate pronounced growth of vacancy clusters at the grain boundaries of as-deposited Al-doped ZnO films deposited as transparent conductive oxide (TCO) on Cu(In, Ga)Se2 (CIGS) solar cells upon accelerated degradation at 85 ◦C/85% relative humidity. Quantitative fractions of positrons trapped either in the vacancy clusters at the grain boundaries or in Zn monovacancies inside the grains of ZnO:Al were obtained by detailed analysis of the PALS data using a positron trapping model. The time and depth dependence of the positron Doppler depth profiles can be accurately described using a planar diffusion model, with an extracted diffusion coefficient of 35 nm2/hour characteristic for in-diffusion of molecules such as H2O andCO2 into ZnO:Al TCO films via the grain boundaries, where they react with the ZnO:Al. This leads to increased open volume at the grain boundaries that imposes additional transport barriers and may lead to charge carrier trapping and nonradiative recombination. Simultaneously, a pronounced increase in series resistance and a strong reduction in efficiency of the ZnO:Al capped CIGS solar cells is observed on a remarkably similar timescale. This strongly indicates that these atomic-scale processes of molecular in-diffusion and creation of open volume at the grain boundaries play a key role in the degradation of the solar cells. PhySH: Solar Cells, Positron Annihilation Spectroscopy, Grain Boundaries, Vacancies, Thin Films, Diffusion, Electrical Properties, Solid State Chemistry, Optoelectronics |
| Databáze: | OpenAIRE |
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