SEMICONDUCTOR THIN FILMS AND THIN FILM DEVICES FOR ELECTROTEXTILES

Abstract

We discuss the evolution from wearable electronics and conductive textiles to electrotextiles with embedded semiconducting films and semiconductor devices and review different semiconductor technologies competing for applications in electrotextiles. We also report on fabrication, characterization, and properties of nanocrystalline semiconductor and metal films and thin-film device structures chemically deposited on fibers, cloth, and large area flexible substrates at low temperatures (close to room temperature). Our approach is based on a new process of depositing polycrystalline CdSe (1.75 eV), CdS (2.4 eV), PbS (0.4 eV), PbSe (0.24 eV) and CuxS (semiconductor/metal) films on flexible substrates from the water solutions of complex-salt compounds. We have covered areas up to 8 × 10 inches but the process can be scaled up. The film properties are strongly affected by processing. We fabricated a lateral solar cell with alternating Cu2-xS and nickel contact stripes deposited on top of a view foil. These sets of contacts represented "ohmic" and "non-ohmic" contacts, respectively. Then CdS films of approximately 0.5 μm thick were deposited on top. We also fabricated a "sandwich" type photovoltaic cell, where the CdS film was sandwiched between an In2O3 layer deposited on a view foil and a Cu2-xS layer deposited on top. Both structures exhibited transient response under light, with the characteristic response time decreasing with the illumination wavelength. This is consistent with having deeper localized states in the energy gap determining the transients for shorter wavelength radiation. (Slow transients related to trapping effects are typical for polycrystalline CdS materials.) We also report on the photovoltaic effect in CdS/CuS films deposited on trylene threads and on a field effect in these films deposited on a flexible copper wire. CdS films deposited on viewfoils exhibit unique behavior under stress and UV radiation exposure with reproducible resistance changes of several orders of magnitude with bending up to 10 mm curvature. Our results clearly demonstrate the feasibility of using this technology for photovoltaic and microelectronics applications for electrotextiles and wearable electronics applications.