| Title |
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 |
| ID_Doc |
65079 |
| Authors |
Shi, WQ; Theelen, M; Illiberi, A; Barreau, N; van der Sar, SJ; Butterling, M; Schut, H; Egger, W; Dickmann, M; Hugenschmidt, C; Zeman, M; Brück, E; Eijt, SWH |
| Title |
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 |
| Year |
2018 |
| Published |
Physical Review Materials, 2.0, 10 |
| Abstract |
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)Se-2 (CIGS) solar cells upon accelerated degradation at 85 degrees 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 nm(2)/hour characteristic for in-diffusion of molecules such as H2O and CO2 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. |
| PDF |
https://repository.tudelft.nl/islandora/object/uuid%3A3fbba0fd-9d2b-465d-b5f9-707cae10656b/datastream/OBJ/download
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