FT-PL Analysis of CIGS/CdS/ZnO Interfaces

High-quality copper indium gallium diselenide (CIGS) films were subjected to a variety of surface treatments attendant to and including deposition of CdS and/or ZnO junctions or buffer layers. The reuslting devices were analyzed at 87 K using Fourier transform photoluminescence (FT-PL) spectroscopy as part of a battery of analytical procedures, including surface analysis, ellipsometry, and I-Vmeasurements, designed to elucidate the influences of the several interfaces on device performance. Our FT-PL system was upgraded with a miniature Joule-Thomson cryostat and a helium-neon laser excitation source to enable collection of highly-resolved, continuous PL spectra from 95-1750 nm. The PL intensity enhancements measured with the upgraded FT-PL system for devices fabricated usingchemical bath deposition (CBD) of CdS, with or without a ZnO electrode, are much greater than for devices incorporating physical vapor deposited (PVD) CdS or ZnO/CIGS interfaces. Exposure of the CIGS films to components of the CBD solution alone, wihtout deposition of CdS, also increases PL intensity, implying a reduction in the rate of non-radiative recombination in the films. Application ofCBD CdS or CBD background solution to the CIGS shifted its PL spectrum to shorter wavelengths, while application of PVD CdS or ZnO to the CIGS broadened its PL spectrum at longer wavelengths.