A polycrystalline Cu(In,Ga)Se₂ (CIGS) single junction solar cell model is developed with dependencies on the molar fraction of In and Ga with a 0.8 eV Shockley-Read-Hall (SRH) trap level above the valence band. The simulated performance of this solar cell over molar fraction compares well to data published in the literature using the SRH minority carrier lifetime to fit the trend in open circuit voltage. The material parameters are then used as a foundation for a numerical model of a monocrystalline CIGS solar cell grown on a GaAs substrate with an emphasis on modeling the CIGS/GaAs interface where a molar fraction gradient in CIGS forms due to lattice mismatch induced inter-diffusion of Ga and In from the substrate and CIGS layers. Without strain effects due to the lattice mismatch, the CIGS monocrystalline solar cell has an efficiency of 18.6% under the AM1.5G spectrum (1000 W/m²) with a short circuit current density of 36.5 mA/cm², an open circuit voltage of 0.66 V and a fill factor of 77.4%. However, when reasonable strain effects are considered, such as the formation of strained induced interface defects and threading dislocation densities (TDD), the efficiency degrades to 6% for TDD < 1x10⁷ cm^-2. The models are able to reproduce a similar structure’s measured performance using a TDD of 1.5×10⁷ cm^-2 and a surface recombination velocity of 10⁸ cm/s at the CdS/CIGS interface.

Date Published: 11 October 2013
PDF: 7 pages
Proc. SPIE 8915, Photonics North 2013, 891507 (11 October 2013); doi: 10.1117/12.2036189

Published in SPIE Proceedings Vol. 8915:
Photonics North 2013
Pavel Cheben; Jens Schmid; Caroline Boudoux; Lawrence R. Chen; André Delâge; Siegfried Janz; Raman Kashyap; David J. Lockwood; Hans-Peter Loock; Zetian Mi, Editor(s)