Omnidirectional sub-bandgap photo-detection using functionalized moulded composite flexible platforms

Abstract The substrate is an optically functional component of a thin film organic optoelectronic device. In the well-known context of photovoltaics, the functionality of substrate is relatively simple – that of a broadband transmittance which allows almost all the incoming light into the absorber. A less explored idea is that of incorporating other optical functionalities in the substrate bulk. Such unconventional design can help surpass the performance limitations of commonly available optoelectronic materials to achieve novel functionality. Bulk functionalization of substrates is particularly easy when the substrates are made using moldable transparent materials which allow mixing of optically functional materials into a composite substrate bulk. In this paper, the example of photonic-upconversion is considered as a representative optical function, to make organic photodetectors which detect up-converted infrared light. By incorporating this functionality in a composite substrate two advantages are demonstrated in which the composite substrate architecture surpasses the performance of the conventional thin film device design. First, the composite substrate preserves the electronic performance of the device by spatially isolating the optical and the charge transport functions. Second, the composite architecture enables sub-bandgap photo-detection which is invariant with respect to the angle of incidence of the infrared input light, by placing the optical function before the light can encounter optically reflecting interfaces. In summary, the unconventional design employing a composite optically functional substrate can be extended to multiple optical functionalities and represents a key design finding that can enable considerably more efficient optoelectronic device designs.