CIGS J-V distortion in the absence of blue photons

Common buffer materials used with CulnGaSe(2) (CIGS) absorbers produce conduction-band barriers that may significantly distort the current-voltage (J-V) curves, especially when short-wavelength photons are excluded from the illumination spectrum. Earlier work documented this effect for CuInSe2 (CIS) absorbers (band gap near 1.0 eV) with CdS buffers. Higher band-gap (similar to 1.15 eV) CIGS absorbers show little or no distortion with CdS buffer layers. However, wider band gap (lower electron affinity) ZnS(O,OH) or InS(O,OH) buffers, prepared by chemical-bath deposition (CBD), clearly show the J-V distortion. The distortions have a turn-on time constant the order of a minute and turn-off time constant the order of a day, and they correlate with major variations in apparent quantum efficiency (QE) measured with varying intensity and spectral content of bias light. The results are consistent with a conduction-band spike barrier that increases with buffer band gap and is larger when the electron concentration in the buffer is small. (c) 2004 Elsevier B.V. All rights reserved.