Indium metal/polymer interfaces

Inverted Device Structures The conventional device structure for PSCs is indium tin oxide (ITO)/PEDOT PSS/polymer blend/Al, where a conductive high-work-function PEDOTPSS layer is used for anode contact, and a low-work-function metal as the cathode. Both the PEDOTPSS layer and the low-work-function metal cathode can cause the degradation of PSCs [110-112]. The acidic PEDOTPSS was reported to etch the ITO and cause interface instability through indium diffusion into the polymer active layer. Low-work-fiinction metals, such as calcium and aluminum, are easily oxidized when exposed to air, increasing the series resistance at the metal/BHJ interface and degrading device performance. 

Consider the polymer-on-metal interface, which might be prepared by coating a thin metal film with polymer in a polymer-based LED. The case of the counter electrode, formed by vapor-deposition, is discussed subsequently. First, assume that the substrates have clean surfaces hydrocarbon and oxide free, or naturally oxidized but still hydrocarbon free (pointed out as necessary). Typically, in connection with polymer-based LEDs, the metallic substrate could be gold, ITO (indium tin oxide) coated glass, the clean natural oxide of aluminum ( 20 A in thickness), the natural oxide which forms upon freshly etched Si( 110) wafers ( 10 A), or possibly even a polyaniline film. Dirt , which may be either a problem or an advantage, will not be taken up here. Discussions will alternate between coated polymer films and condensed model molecular solid films, as necessary to illustrate points. 

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