Abstract
Utilizing Bragg surface plasmon polaritons (SPPs) on metal nanostructures for the use in optical devices has been intensively investigated in recent years. Here, we demonstrate the integration of nanostructured metal electrodes into an ITO-free thin film bulk heterojunction organic solar cell, by direct fabrication on a nanoimprinted substrate. The nanostructured device shows interesting optical and electrical behavior, depending on angle and polarization of incidence and the side of excitation. Remarkably, for incidence through the top electrode, a dependency on linear polarization and angle of incidence can be observed. We show that these peculiar characteristics can be attributed to the excitation of dispersive and non-dispersive Bragg SPPs on the metal–dielectric interface on the top electrode and compare it with incidence through the bottom electrode. Furthermore, the optical and electrical response can be controlled by the organic photoactive material, the nanostructures, the materials used for the electrodes and the epoxy encapsulation. Our device can be used as a detector, which generates a direct electrical readout and therefore enables the measuring of the angle of incidence of up to 60° or the linear polarization state of light, in a spectral region, which is determined by the active material. Our results could furthermore lead to novel organic Bragg SPP-based sensor for a number of applications.
Highlights
In recent years, substantial research in the field of nanophotonics has targeted the understanding and manipulation of light–matter interactions on the nanoscale
With excitation through the thin bottom electrode (BI), the device acts as an ITO-free organic solar cell with a considerable power conversion efficiency (PCE) of 1.88% and an external quantum efficiency (EQE) of up to 30% without performing any optimization
We conclusively present that with top incidence (TI) the coupling of light to Bragg surface plasmon polaritons (SPPs) modes on the corrugated top metal–epoxy interface occurs and that this coupling and the subsequent absorption and charge carrier generation in the device allows for an angle of incidence (AOI) and polarization dependent response
Summary
Substantial research in the field of nanophotonics has targeted the understanding and manipulation of light–matter interactions on the nanoscale. The coupling condition of dispersive SPPs depends on the periodicity of the grating and the angle of incidence and the polarization state of the incoming light [18]. The advantages of Bragg SPPs, such as easy excitation, the angular dependent coupling condition, polarization sensitivity, as well as the field enhancements, are widely used in surface plasmon resonance (SPR) sensors [19,20,21,22], for surface plasmon coupled light emission [23], in photo detectors [11,24] and in plasmonic solar cells [12,25,26,27,28]
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