Photoluminescence and time‐resolved photoluminescence in Cu(In,Ga)Se₂ thin films and solar cells

Abstract

Photoluminescence (PL) and time‐resolved PL (TR‐PL) studies have been carried out on Cu(In,Ga)Se2 (CIGS) thin films and solar cells (ZnO/CdS/CIGS) to study the recombination of the photo‐excited carriers. The CIGS solar cells exhibited intense near‐band‐edge (NBE) PL compared with the CIGS films by two orders of magnitude. PL decay time of the cell is strongly dependent on the repetition frequency of the excitation light. PL decay time of the cell is longer than that of the corresponding CIGS thin film. The chemical bath deposition of the CdS buffer layer on CIGS leads to changes in PL intensity, defect‐related PL and the PL decay time. They are discussed with relation to the substitution of Cd atom at the Cu site at the Cu‐deficient surface of CIGS thin film. Under the open circuit condition, NBE‐PL is stronger and the decay time is longer compared with those under the short circuit condition. PL of the cell under the load was examined, and PL intensity and PL decay time are related to the photovoltage during PL measurements. Low temperature PL suggests that the Cd diffusion during the CBD process is pronounced for low Ga content CIGS. The authors demonstrate the effectiveness of PL as a powerful non‐destructive device and photovoltaic characterization methods of CIGS solar cells. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Influence of Flash Lamp Annealing on the Optical Properties of CIGS Layer

“…Figure 2a shows the room-temperature photoluminescence spectra obtained from virgin and ash lamp annealed samples. The PL spectrum of the virgin sample consists of broad band with a maximum intensity located at 1210 nm due to near-band-edge emission and free-to--bound (FB) transition at about 1250 nm [21,22]. The ash lamp annealing leads to an enhancement of the maximum NBE-PL intensity and shifts its position of about 10 nm to the longer wavelength (smaller band gap) and the separation between the two observed emissions (NBE and FB) is clearly visible.…”

Characterization of Cu(In,Ga)Se2 Solar Cell Fabrication Process by Photoluminescence

“…1 and 2, which is much smaller than the ratio of the PL intensity in the CIGS solar cell under the oc condition to that in the sc condition, which is approximately 10 2 . 6) Based on load resistance dependence of PL intensity in the CIGS solar cell, 5) the shunt resistance of the ZnO:Al/ZnO/CdS/CIGS film has been tentatively estimated to be less than 1 k.…”

“…In this stage, the heterojunction operates under the sc condition, which leads to the low PL yield, similar to PL intensity in the CIGS solar cell under the sc condition. [5][6][7]17,18) The low PL yield under the sc condition is due to the decrease in the radiative recombination of photo-excited electrons caused by the high charge separation field of the depletion layer. After the mechanical scribing for the cell isolation, PL intensity recovers up to the level of the as-grown CIGS films.…”

Modeling a monocrystalline Cu(In,Ga)Se2single junction solar cell grown on a GaAs substrate

“…The SRH lifetime was studied using two approaches: 1) a constant lifetime of 3 ns over the range of molar fractions [13], and 2) a lifetime which gives good agreement to the open circuit voltage as obtained in the literature. This latter approach can be hypothetically justified by a change in the trap energy level with respect to the conduction band located at a fixed energy of 0.8 eV from the valence band [2].…”