Optimization of chemically deposited CuxS solar control coatings

Abstract

CuxS thin films appropriate for use as solar control coatings for architectural glazing applications have been deposited from chemical baths constituted from copper(II) nitrate or chloride, NH3(aq), NaOH, triethanolamine and thiourea. At ambient temperature (25 degrees C), the duration of deposition ranges from 2 to 12 h, but at 50 degrees C, deposition can be considerably faster, from 1 h to 2 h 50 min. CuxS films deposited in this manner require air annealing at 150 degrees C for about 10 min, to reduce the integrated infrared transmittance, T*(IR), to about 10%. The corresponding integrated transmittance in the visible region, T*(vis), is about 30% and the integrated transmittance for AM2 solar spectra is about 20%. The optical transmittance spectra of the annealed films are peaked in the 0.55-0.575 mu m wavelength range, which provides a greenish yellow illumination inside the building under daylight, that corresponds to the peak in the spectral sensitivity curve of the human eye for photopic (daylight) vision. The reduction in sheet resistance of the CuxS films with the air annealing, from about M Omega Square Operator -1 to about 10-100 Omega Square Operator -1, ensures a low thermal emittance which is a requirement for high-efficiency solar control coatings. The issues involved in the optimization of the deposition conditions for large-area production of the coatings and the choice of protective polymer coatings are also discussed.