Examination of Na-Doped Mo Sputtering for CIGS Devices: Cooperative Research and Development Final Report, CRADA Number CRD-10-375

This work has investigated the use of Na doped Mo (MONA) sputtering targets for use in preparing CIGS devices. The Mo:Na material is doped to about 3% Na by weight, implying that a 40 nm layer on top of the standard Mo contact contains sufficient Na to dope a 2.5 ..mu..m CIGS film. The ability to control Na doping independent of both CIGS processing conditions and adhesion is an important gain for industry and research. Manufacturers gain a route to increased manufacturability and performance, while NREL researchers gain a tightened performance distribution of devices and increased process flexibility. Our immediate partner in this work, the Climax Molybdenum Technology Center, gains validation of their product

The Effect of Cu Zn Disorder on Charge Carrier Mobility and Lifetime in Cu2ZnSnSe4

Cu Zn disorder is one possible origin for the limited efficiencies of kesterite solar cells and its impact on the band gap and band tails have been intensively studied. However, the effect on charge transport and recombination, which are key properties for solar cells, has not been investigated so far. Therefore, we probe the impact of the Cu Zn order on charge carrier mobility and lifetime. To this end, we change the Cu Zn order of a co evaporated Cu2ZnSnSe4 thin film by sequential annealing and probe the impact by time resolved terahertz spectroscopy. Aside from of the well known band gap shift, we find no significant change in mobility and lifetime with Cu Zn order. This finding indicates that Cu Zn disorder is not limiting efficiencies of kesterite solar cells at their current status by means of charge carrier recombination and transpor

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

Zn Se Cd S Interlayer Formation at the CdS Cu2ZnSnSe4 Thin Film Solar Cell Interface

The chemical structure of the CdS/Cu2ZnSnSe4 (CZTSe) interface was studied by a combination of electron and X-ray spectroscopies with varying surface sensitivity. We find the CdS chemical bath deposition causes a "redistribution" of elements in the proximity of the CdS/CZTSe interface. In detail, our data suggest that Zn and Se from the Zn-terminated CZTSe absorber and Cd and S from the buffer layer form a Zn-Se-Cd-S interlayer. We find direct indications for the presence of Cd-S, Cd-Se, and Cd-Se-Zn bonds at the buffer/absorber interface. Thus, we propose the formation of a mixed Cd(S,Se)-(Cd,Zn)Se interlayer. We suggest the underlying chemical mechanism is an ion exchange mediated by the amine complexes present in the chemical bath

Characterization of 19.9% Efficient CIGS Absorbers: Preprint

This paper documents the properties of the world-record-efficiency CIGS solar cell by a variety of characterization techniques, with an emphasis on identifying near-surface properties associated with the modified processing

Electrical, morphological and structural properties of RF magnetron sputtered Mo thin films for application in thin film photovoltaic solar cells

Molybdenum (Mo) thin films were deposited using radio frequency magnetron sputtering, for application as a metal back contact material in ‘‘substrate configuration’’ thin film solar cells. The variations of the electrical, morphological, and structural properties of the deposited films with sputtering pressure, sputtering power and post-deposition annealing were determined. The electrical conductivity of the Mo films was found to increase with decreasing sputtering pressure and increasing sputtering power. X-ray diffraction data showed that all the films had a (110) preferred orientation that became less pronounced at higher sputtering power while being relatively insensitive to process pressure. The lattice stress within the films changed from tensile to compressive with increasing sputtering power and the tensile stress increased with increasing sputtering pressure. The surface morphology of the films changed from pyramids to cigar-shaped grains for a sputtering power between 100 and 200 W, remaining largely unchanged at higher power. These grains were also observed to decrease in size with increasing sputtering pressure. Annealing the films was found to affect the resistivity and stress of the films. The resistivity increased due to the presence of residual oxygen and the stress changed from tensile to compressive. The annealing step was not found to affect the crystallisation and grain growth of the Mo films

Secondary crystalline phases identification in Cu2ZnSnSe4 thin films: contributions from Raman scattering and photoluminescence

In this work, we present the Raman peak positions of the quaternary pure selenide compound Cu2ZnSnSe4 (CZTSe) and related secondary phases that were grown and studied under the same conditions. A vast discussion about the position of the X-ray diffraction (XRD) reflections of these compounds is presented. It is known that by using XRD only, CZTSe can be identified but nothing can be said about the presence of some secondary phases. Thin films of CZTSe, Cu2SnSe3, ZnSe, SnSe, SnSe2, MoSe2 and a-Se were grown, which allowed their investigation by Raman spectroscopy (RS). Here we present all the Raman spectra of these phases and discuss the similarities with the spectra of CZTSe. The effective analysis depth for the common back-scattering geometry commonly used in RS measurements, as well as the laser penetration depth for photoluminescence (PL) were estimated for different wavelength values. The observed asymmetric PL band on a CZTSe film is compatible with the presence of CZTSe single-phase and is discussed in the scope of the fluctuating potentials’ model. The estimated bandgap energy is close to the values obtained from absorption measurements. In general, the phase identification of CZTSe benefits from the contributions of RS and PL along with the XRD discussion.info:eu-repo/semantics/publishedVersio