XPS AND UPS investigation of NH/sub 4/OH-exposed Cu(In,Ga)Se/sub 2/ thin films
Photoelectron spectroscopy was used to determine the compositional and electronic changes occurring in Cu(In,Ga)Se/sub 2/ thin films as a result of immersion in aqueous ammonia solution. We find that NH/sub 4/OH-treated CIGS surfaces are preferentially etched of indium and gallium, resulting in the formation of a thin layer of a degenerate Cu-Se compound that we tentatively identify as Cu/sub 2/Se. The work function of ammonia-treated samples is found to increase by 0.6 eV relative to as-grown CIGS thin films. The uniformity of chemical bath effects (etching & deposition) was found to be improved by the addition to the bath of a non-ionic surfactant. Initial device results show that the new surfactant-based chemical bath deposition (CBD) method may lead to better and thinner CdS buffer layers.
Skin Deep: Highlights of NREL Surface Analysis PV Research
The Surface Analysis project provides measurement support and leadership for collaborative research activities involving surface chemistry and physics in all areas of the PV program. Significant results from the past fiscal year include the following: i) in-situ XPS, UPS, and AES studies of chemical-bath exposure of CIGS surfaces demonstrated that Group-III elements are preferentially removed from the surface, that type conversion of the surface occurs, and that the addition of a surfactant improves CdS deposition and thus device performance; ii) XPS studies of polyethylene terephthalate (PET) candidate backsheet materials have shown that plasma exposure prior to oxide-barrier deposition results in the formation of low-molecular-weight fragments that result in the formation of a weak interfacial layer that fails during damp-heat exposure; iii) an empirical relation was derived for the source geometry that leads to optimal film-thickness uniformity in rotating-substrate physical-vapor deposition (PVD) systems; and iv) PVD flux-distribution calculations were performed to develop a novel method for combinatorial thin-film synthesis.
Synthesis and chemical recycling of novel poly(ester-urethane)s using an enzyme.
A series of enzymatically recyclable poly(ester-urethane)s consisting of a biodegradable diurethane moiety as a hard segment and an ester moiety as an enzymatically cleavable linkage was chemo-enzymatically prepared by two routes. The poly(ester-urethane) was prepared by a) the ring-opening polymerization of a cyclic ester-urethane monomer synthesized via the transesterification reaction of biodegradable diurethanediol and dicarboxylate ester using lipase and b) the direct polycondensation of a diurethanediol and a dicarboxylate ester. A significantly higher molecular-weight poly(ester-urethane) having the highest molecular weight (Mw) of 101,000 was produced by the ring-opening polymerization of the cyclic ester-urethane monomer when compared with that produced by the polycondensation of the dicarboxylate ester with diurethanediol. The poly(ester-urethane) was readily degraded by lipase into the corresponding cyclic oligomers; the oligomers were readily repolymerized by the ring-opening polymerization using lipase for chemical recycling.