Evolution and role of vacancy clusters at grain boundaries of ZnO:Al during accelerated degradation of Cu(In, Ga)Se-2 solar cells revealed by positron annihilation

Evolution and role of vacancy clusters at grain boundaries of ZnO:Al during accelerated degradation of Cu(In, Ga)Se-2 solar cells revealed by positron annihilation

Shi, W. (TU Delft RST/Fundamental Aspects of Materials and Energy)
Theelen, Mirjam (TNO)
Illiberi, Andrea (TNO)
van der Sar, S.J. (TU Delft Applied Sciences)
Butterling, M. (TU Delft RST/Fundamental Aspects of Materials and Energy)
Schut, H. (TU Delft RST/Neutron and Positron Methods in Materials)
Zeman, M. (TU Delft Electrical Sustainable Energy)
Brück, E.H. (TU Delft RST/Fundamental Aspects of Materials and Energy)
Eijt, S.W.H. (TU Delft RST/Fundamental Aspects of Materials and Energy)

Applied Sciences

Electrical Sustainable Energy

2018

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

PhySH: Solar Cells
Positron Annihilation Spectroscopy
Grain Boundaries
Vacancies
Thin Films
Diffusion
Electrical Properties
Solid State Chemistry
Optoelectronics

http://resolver.tudelft.nl/uuid:3fbba0fd-9d2b-465d-b5f9-707cae10656b

https://doi.org/10.1103/PhysRevMaterials.2.105403

2475-9953

Physical Review Materials, 2 (10)

Institutional Repository

journal article

© 2018 W. Shi, Mirjam Theelen, Andrea Illiberi, S.J. van der Sar, M. Butterling, H. Schut, M. Zeman, E.H. Brück, S.W.H. Eijt, More Authors