Damp-Heat Induced Degradation of Transparent Conducting Oxides for Thin Film Solar Cells

The objectives are: (1) To achieve a high long-term performance reliability for the thin-film CIGS PV modules with more stable materials, device structure designs, and moisture-resistant encapsulation materials and schemes; (2) to evaluate the DH stability of various transparent conducting oxides (TCOs); (3) to identify the degradation mechanisms and quantify degradation rates; (4) to seek chemical and/or physical mitigation methods, and explore new materials. It's important to note that direct exposure to DH represents an extreme condition that a well-encapsulated thin film PV module may never experience

Damp-Heat Induced Degradation of Transparent Conducting Oxides for Thin-Film Solar Cells: Preprint

The stability of intrinsic and Al-doped single- and bi-layer ZnO for thin-film CuInGaSe2 solar cells, along with Al-doped Zn1-xMgxO alloy and Sn-doped In2O3 (ITO) and F-doped SnO2, was evaluated by direct exposure to damp heat (DH) at 85oC and 85% relative humidity. The results show that the DH-induced degradation rates followed the order of Al-doped ZnO and Zn1-xMgxO >> ITO > F:SnO2. The degradation rates of Al:ZnO were slower for films of higher thickness, higher substrate temperature in sputter-deposition, and with dry-out intervals. As inferred from the optical micro-imaging showing the initiation and propagation of degrading patterns and regions, the degradation behavior appears similar for all TCOs, despite the obvious difference in the degradation rate. A degradation mechanism is proposed to explain the temporal process involving thermal hydrolysis

Investigation of Cd1-XMgxTe Alloys for Tandem Solar Cell Applications: Preprint

Theoretical modeling of two-junction tandem solar cells shows that for optimal device performance, the bandgap of the top cell should be in the range of 1.6 to 1.8 eV. Cd1-xMgxTe (CMT) alloys have a lattice constant close to that of CdTe, and the addition of a small amount of Mg changes the bandgap considerably. In this paper, we present our work on developing CMT for solar cell applications. CMT films were prepared by vacuum deposition with co-evaporation of CdTe and Mg on substrates heated to 300-400 C. Films with a composition in the range of x = 0 to 0.66 were fabricated, and optical analysis of the films showed that the bandgap of the samples ranged from 1.5 to 2.3 eV and varied linearly with composition. For the fabrication of devices using these alloy films, we also investigated the effect of post-deposition CdCl2 heat treatment. We have investigated junctions between CdS and CMT alloys in the bandgap range of 1.5 to 1.8 eV for tandem cell applications. We have also worked on the ohmic contacts to the CMT alloy films using Cu/Au bilayers, and the preliminary data shows a significant effect of the contact processing on the device performance

Degradation of ZnO Window Layer for CIGS by Damp-Heat Exposure: Preprint

This paper summarizes our work with more details and an emphasis on the DH-induced degradation of Al-doped ZnO and Zn1-xMgxO alloys. The other two TCOs, ITO and F:SnO2, are not included here

Dependence of the Characteristics of Mo Films on Sputter Conditions

The residual stress, resistance, orientation, and microstructure of sputtered Mo films were studied as a function of varied-deposition power and pressure

Comparative Study of the Defect Point Physics and Luminescence of the Kesterites Cu2ZnSnS4 and Cu2ZnSnSe4 and Chalcopyrite Cu(In,Ga)Se2: Preprint

In this contribution, we present a comparative study of the luminescence of the kesterites Cu2ZnSnS4 (CZTS) and Cu2ZnSnSe4 (CZTSe) and their related chalcopyrite Cu(In,Ga)Se2 (CIGSe). Luminescence spectroscopy suggests that the electronic properties of Zn-rich, Cu-poor kesterites (both CZTS and CZTSe) and Cu-poor CIGSe are dictated by fluctuations of the electrostatic and chemical potentials. The large redshift in the luminescence of grain boundaries in CIGSe, associated with the formation of a neutral barrier is clearly observed in CZTSe, and, to some extent, in CZTS. Kesterites can therefore replicate the fundamental electronic properties of CIGSe