Investigating the electronic properties of Al2O3/Cu(In, Ga)Se-2 interface

Abstract

Atomic layer deposited (ALD) Al2O3 films on Cu(In, Ga)Se-2 (CIGS) surfaces have been demonstrated to exhibit excellent surface passivation properties, which is advantageous in reducing recombination losses at the rear metal contact of CIGS thin-film solar cells. Here, we report, for the first time, experimentally extracted electronic parameters, i.e. fixed charge density (Q(f)) and interface-trap charge density (D-it), for as-deposited (AD) and post-deposition annealed (PDA) ALD Al2O3 films on CIGS surfaces using capacitance-voltage (C-V) and conductance-frequency (G-f) measurements. These results indicate that the AD films exhibit positive fixed charges Q(f) (approximately 10(12) cm(-2)), whereas the PDA films exhibit a very high density of negative fixed charges Q(f) (approximately 10(13) cm(-2)). The extracted D-it values, which reflect the extent of chemical passivation, were found to be in a similar range of order (approximately 10(12) cm(-2) eV(-1)) for both AD and PDA samples. The high density of negative Q(f) in the bulk of the PDA Al2O3 film exerts a strong Coulomb repulsive force on the underlying CIGS minority carriers (n(s)), preventing them to recombine at the CIGS/Al2O3 interface. Using experimentally extracted Q(f) and D-it values, SCAPS simulation results showed that the surface concentration of minority carriers (n(s)) in the PDA films was approximately eight-orders of magnitude lower than in the AD films. The electrical characterization and estimations presented in this letter construct a comprehensive picture of the interfacial physics involved at the Al2O3/CIGS interface. (C) 2015 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.