Although the detection of light at terahertz (THz) frequencies is important for a large range of applications, current detectors typically have several disadvantages in terms of sensitivity, speed, operating temperature, and spectral range. Here, we use graphene as photoactive material to overcome all of these limitations in one device. We introduce a novel detector for terahertz radiation that exploits the photo-thermoelectric effect, based on a design that employs a dual-gated, dipolar antenna with a gap of ∼100 nm. This narrow-gap antenna simultaneously creates a pn-junction in a graphene channel located above the antenna, and strongly concentrates the incoming radiation at this pn-junction, where the photoresponse is created. We demonstrate that this novel detector has excellent sensitivity, with a noise-equivalent power of 80 pW/ √ Hz at room temperature, a response time below 30 ns (setup-limited), a high dynamic range (linear power dependence over more than 3 orders of magnitude) and broadband operation (measured range 1.8 -4.2 THz, antenna-limited), which fulfills a combination that is currently missing in the state of the art. Importantly, based on the agreement we obtain between experiment, analytical model, and numerical simulations, we have reached a solid understanding of how the PTE effect gives rise to a THz-induced photoresponse, which is very valuable for further detector optimization.

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Integrating and manipulating the nano-optoelectronic properties of Van der Waals heterostructures can enable unprecedented platforms for photodetection and sensing. The main challenge of infrared photodetectors is to funnel the light into a small nanoscale active area and efficiently convert it into an electrical signal. Here, we overcome all of those challenges in one device, by efficient coupling of a plasmonic antenna to hyperbolic phonon-polaritons in hexagonal-BN to highly concentrate mid-infrared light into a graphene pn-junction. We balance the interplay of the absorption, electrical and thermal conductivity of graphene via the device geometry. This approach yields remarkable device performance featuring room temperature high sensitivity (NEP of 82 pW$$/\sqrt{{\bf{Hz}}}$$ / Hz ) and fast rise time of 17 nanoseconds (setup-limited), among others, hence achieving a combination currently not present in the state-of-the-art graphene and commercial mid-infrared detectors. We also develop a multiphysics model that shows very good quantitative agreement with our experimental results and reveals the different contributions to our photoresponse, thus paving the way for further improvement of these types of photodetectors even beyond mid-infrared range.

A universal strategy for efficient light trapping through the incorporation of gold nanorods on the electron transport layer (rear) of organic photovoltaic devices is demonstrated. Utilizing the photons that are transmitted through the active layer of a bulk heterojunction photovoltaic device and would otherwise be lost, a significant enhancement in power conversion efficiency (PCE) of poly[N‐9′‐heptadecanyl‐2,7‐carbazole‐alt‐5,5‐(4′,7′‐di‐2‐thienyl‐2′,1′,3′‐benzothiadiazole)]:phenyl‐C71‐butyric acid methyl ester (PCDTBT:PC71BM) and poly[[4,8‐bis[(2‐ethylhexyl)oxy]benzo[1,2‐b:4,5‐b′]dithiophene‐2,6‐diyl][3‐fluoro‐2‐[(2‐ethylhexyl)carbonyl]thieno[3,4‐b] thiophenediyl]] (PTB7):PC71BM by ≈13% and ≈8%, respectively. PCEs over 8% are reported for devices based on the PTB7:PC71BM blend. A comprehensive optical and electrical characterization of our devices to clarify the influence of gold nanorods on exciton generation, dissociation, charge recombination, and transport inside the thin film devices is performed. By correlating the experimental data with detailed numerical simulations, the near‐field and far‐field scattering effects are separated of gold nanorods (Au NRs), and confidently attribute part of the performance enhancement to the enhanced absorption caused by backscattering. While, a secondary contribution from the Au NRs that partially protrude inside the active layer and exhibit strong near‐fields due to localized surface plasmon resonance effects is also observed but is minor in magnitude. Furthermore, another important contribution to the enhanced performance is electrical in nature and comes from the increased charge collection probability.

Incorporating plasmonic nanoparticles in organic photovoltaic (OPV) devices can increase the optical thickness of the organic absorber layer while keeping its physical thickness small. However, trade-offs between various structure parameters have caused contradictions regarding the effectiveness of plasmonics in the literature, that have somewhat stunted the progressing of a unified theoretical understanding for practical applications. We examine the o p t i c a l e n h a n c e m e n t m e c h a n i s m s o f p r a c t i c a l PCDTBT:PC 70 BM OPV cells incorporating metal nanoparticles. The plasmonic near-and far-field contributions are differentiated, with spectrum-and space-wide current enhancements found in the plasmon scattering regime and spectrum-and space-specific current enhancements in the near-field regime. A remarkable system complexity is revealed, where the plasmonic enhancement trends change and even reverse by simple changes in the device geometry. This accounts for many of the contradictory results published in the literature on plasmonic effects in OPVs. By exploring the full structural parameter phase-space we are able to now propose a unified representation that intuitively explains literature findings and trends. Our results show that an already optimized PCDTBT:PC 70 BM cell can be further optically enhanced by plasmonic effects by at least 20% with the incorporation of Ag nanoparticles.