Owing to the excellent light sensitivity of organic semiconductors along with the other advantages like low temperature processing, ease of material synthesis with versatile bandgap tunability, mechanical flexibility and printability, these materials have shown considerable potential in realizing organic photodetector (OPD) and organic photovoltaic (OPV) devices towards indoor and internet of things (IoT) applications. In this context, bulk-heterojunction (BHJ) system, comprising the blend of donor (p-type) and acceptor (n-type) materials, is one of the most efficient approaches to achieve effective photo-generation of charge carriers. In recent past, a BHJ system, consisting of in-house synthesized donor molecule and readily available acceptor molecule, has been employed to realize ultraviolet (UV) OPD in our laboratory for UV-A sensing.

This seminar will mainly focus on the OPV devices based on BHJ system and the strategy for improving the device performance. Solvent additive techniques along with annealing methodology to intensify the interpenetrating bicontinuous network of donor and acceptor materials across the bulk of the thin film will be discussed. In particular, the impact of the solvent additives such as diphenyl sulfide and diphenyl sulphoxide (where the latter was synthesized in the Chemistry Department, IIT Madras) on the power conversion efficiency of OPV devices will be presented. Finally, the appearance of ambipolar charge carriers in BHJ semiconductor-based metal-insulator-semiconductor (MIS) capacitor devices will be demonstrated for the first time. Appearance of unipolar and ambipolar capacitance-voltage characteristics depending on the blend ratio can be considered as a diagnostic approach to predict the performance of the devices requiring ambipolar charge transport.