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Selective doping of a Zn impurity at the group III site in a Cu(In, Ga)Se2 (CIGS) film was performed by the doping of Zn at the first stage of the three-stage method. The p-type CIGS:Zn film was obtained, which is in contrast to the n-type CIGS:Zn film obtained by the Zn impurity doping at the second and third-stages. Based on excitation intensity dependence of photoluminescence (PL) at low-temperature, the change in the acceptor level was observed. The enhancement of carrier concentration as a result of Zn-doping in the p-type CIGS:Zn film was observed. The CIGS:Zn solar cells exhibited η of 14.5% and Voc of 0.658 V, which are higher than that of the corresponding solar cells using the undoped CIGS films [ABSTRACT FROM AUTHOR]

Photoluminescence (PL) has been reviewed for the characterization of Cu(In,Ga)Se2 (CIGS) solar cells with emphasis on PL intensity and lifetime in the photovoltaic heterojunction, characterization of photovoltage by PL mapping, PL in CIGS solar process, and degradation of CIGS surface in air. [ABSTRACT FROM AUTHOR]

The photo-acoustic spectroscopy (PAS) using a transparent piezoelectric photo-thermal (Tr-PPT) method was carried out on Cu(In,Ga)Se2 (CIGS) thin films (both CIGS/Mo/SLG and CdS/CIGS/Mo/SLG) and solar cells (ZnO/CdS/CIGS/Mo/SLG). Using the Tr-PPT method, the high background absorption in the below gap region observed in both a microphone and a conventional transducer PAS spectra was strongly reduced. This high background absorption came from the CIGS/Mo interface. This result proves that the Tr-PPT PAS is the surface sensitive method. In the below-band region, a bell-shape deep absorption band has been observed at 0.76 eV, in which a full-width at the half-maximum value was 70-120 meV. This deep absorption band was observed for both CdS/CIGS/Mo/SLG and ZnO/CdS/CIGS/Mo/SLG structures. The peak energy of the absorption band was independent of the alloy composition for 0.25≤Ga/III≤0.58. Intensity of the PA signal was negatively correlated to the Na concentration at the CIGS film surface. The origin of the 0.76 eV peak is discussed with relation to native defects such as a Cu-vacancy-related defect (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

A series of studies on photoluminescence (PL) and time-resolved PL in Cu(In,Ga)Se2 (CIGS) solar cells is presented with emphasis on the photovoltaic effect in the ZnO/CdS/CIGS heterostructure. The photovoltage created by an excitation light increases PL yield and PL decay time of the near-band-edge PL of the CIGS absorber layer in the CIGS solar cell. Under the open circuit condition, the photovoltage reduces the carrier separation field in the space charge region. This reduces the collection of photoexcited carriers, which results in the high PL yield and long PL decay time. The two-dimensional PL intensity mapping of the CIGS solar cell reflects the photovoltage distribution, and the results are compared with the light-beam-induced current image. PL characterization of the CIGS solar cell process has been studied. A chemical-bath deposition of the CdS buffer layer and the following sputter-deposition of the high-resistivity ZnO buffer layer do not change PL intensity and PL decay time of the CIGS layer. On the other hand, a metalorganic chemical vapor deposition (MOCVD) of the high-resistivity ZnO layer leads to high PL intensity and the long PL decay time. The result is discussed in terms of the thermal diffusion of Cd from CdS layer into the CIGS absorber layer during the MOCVD process at an elevated temperature. The formation of the buried pn junction in the CIGS layer due to the Cd-diffusion is discussed in terms of an electron-beam induced current measurement. The utilization of PL as a measure of the junction formation is discussed. [ABSTRACT FROM AUTHOR]

An attempt is made to dope Zn impurity selectively at the In site in Cu(In,Ga)Se2 (CIGS) by supplying Zn at the first stage of a three‐stage method. Increase in carrier concentration in p‐type CIGS leads to increase in an open circuit voltage and a conversion efficiency (η). The Zn impurity loaded in (In,Ga)2Se3 a the 1st stage is expected to make a substitutional ZnIn acceptor in CIGS, which leads to increase in carrier concentration. The Zn doping profile at the 1st stage is expected to be reflected in the acceptor (ZnIn) depth profile. Acceptor in‐depth profile is expected to be changed by the Zn flux. The room‐temperature PL spectra of the CIGS:Zn exhibited peak shift to higher energy by 10–50 meV depending on the Zn‐doping condition due to the change of band gap energy. The carrier in‐depth profile is characterized using a capacitance‐voltage method for ZnO/CdS/CIGS:Zn solar cells. Carrier concentration of Zn‐loaded samples increase by one order of magnitude as compared with that in the intentionally undoped CIGS samples. The relationship between the Zn‐doping profile and solar cell characteristics is examined. Results are also discussed in terms of the back surface field created by the Zn‐doping profile. [ABSTRACT FROM AUTHOR]