Light induced electro-luminescence patterning: interface energetics modification at semiconducting polymer and metal-oxide heterojunction in a photodiode
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Understanding the injection barriers and defect states at the metal−organic or inorganic−organic interfaces is one of the key challenges in improving the efficiency of hybrid electronic devices. In this paper, polymer and metal-oxide-based photodiodes are subjected to light soaks to probe the interface and bulk induced defects and energetics. Polymers poly(3-hexylthiophene-2,5-diyl) and poly[N-9′-heptadecanyl-2,7-carbazole-alt- 5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] were used as active medium in an “inverted” sandwich-type device configuration to study the effect of light soak on current− voltage, charge trapped and stored, electroluminescence, photovoltage, and photocurrent characteristics. The results collectively demonstrate a modification to the cathode contact and polymer interface energetics. Ultraviolet (UV)-assisted photodesorption of oxidizing agents at the interface of nanostructured zinc oxide derived from a sol−gel precursor and the polymer lowers the magnitude of cathode work function. As a result, we have realized an efficient light-emitting diode stencilled out of the diode after UV exposure. The work function and interface barrier modification followed by energy band bending within the device is proposed. Our results emphasize the role of unintentional injection barriers and a solution to the issue often encountered in the hybrid organic−inorganic electronic devices.