Embedded organic hetero-junction and negative-differential-resistance photocurrent based on bias-assisted natural-drying of organic drops

This work reports a bias-assisted natural-drying method in film drop-casting for the formation of an interfacial layer inside the bulk organic film. The natural-drying facilitates phase segregation in the polymer blend, while the simultaneous substrate bias application induces host electronic states in the interfacial layer. Consequently, an embedded organic hetero-junction is formed between the interfacial layer and bulk film. The hetero-junction not only enhances the separation of photoexcited electron–hole (ep-hpep-hp) pairs, but also allows for the selective storage and extraction of photocarriers through the bias-induced host states. Unusual photocurrent with negative-differential-resistance (NDR) is thus obtained for the first time for organic optoelectronic devices. The typical peak-to-valley ratio of the NDR peak is ⩾500, and the NDR behavior is stable for prolonged photocurrent measurements. The bias-assisted natural-drying method is simple and cost-effective, and can be used as a new approach to the design and control of organic interfaces.