Optical and Electrical Properties of Organic Semiconductor Thin Films on Aperiodic Plasmonic Metasurfaces

Metal electrodes are playing an increasingly important role in controlling photon absorption and in promoting optimal light management in thin-film semiconductor devices. For organic optoelectronic devices, the conventional fabrication approach is to build the device on top of a transparent electrode, with metal electrode deposition as the last step. This makes it challenging to control the surface of the metal electrode to promote good light management properties. An inverted fabrication approach that builds the device on top of a metal electrode makes it possible to control the morphology of the metal surface independently of the organic semiconductor active layer to achieve a variety of photonic and plasmonic behaviors useful for devices. However, there are few reports of inverted fabrication of organic optoelectronic devices and its impacts on device properties. Silver (Ag) is the most suitable metal for fabrication of nanostructured electrodes with plasmonic behavior (i.e., plasmonic electrodes) because of its low parasitic absorption loss and high reflectivity. In this project, we describe the facile fabrication of silver nanoparticle (AgNP) aperiodic plasmonic metasurfaces and study their physical and optical characteristics. Then, we investigate the photonic and electrical behaviors of the aperiodic plasmonic metasurfaces when interfaced with poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT) organic semiconducting polymer thin films. The luminescence quantum yield of F8BT thin films increases from 29% on planar Ag up to 66% on AgNP metasurfaces due to the Purcell effect and the improved extraction of emission coupled to surface plasmon polariton modes. In particular, we show that plasmonic enhancement can overcome ohmic losses associated with metals and metal-induced exciton quenching. According to the current-voltage characteristics of hole-only devices with and without aperiodic plasmonic metasurfaces, we conclude that AgNP aperiodic plasmonic metasurfaces have comparable electrical behavior to planar metal electrodes while having superior light management capability.

Plasmonic Effects of Silver Nanoparticles Embedded in the Counter Electrode on the Enhanced Performance of Dye-Sensitized Solar Cells

The plasmonic effects of silver (Ag) nanoparticles (NPs) with various morphologies (sphere, rod, and prism) embedded into the platinum (Pt) counter electrodes (CEs) of dye-sensitized solar cells (DSCs) were systematically investigated. It was shown that the power conversion efficiencies (PCEs) of the incorporated devices are notably improved from 7.60%, for the reference device without Ag NPs, to 8.10, 8.68, and 8.55% with Ag nanospheres, nanorods, and nanoprism devices, respectively. Moreover, the photocurrent and fill factor enhancement is attributed to the better optical and electrical properties of the integrated devices. Among all of the NP morphologies studied, Ag nanorods offer the best improvement to the device efficiency, as they have longitudinal localized surface plasmon resonance (L-LSPR) and strong scattering effects correlate within the morphology.

Interfacial Materials for Organic Solar Cells: Recent Advances and Perspectives

Organic solar cells (OSCs) have shown great promise as low-cost photovoltaic devices for solar energy conversion over the past decade. Interfacial engineering provides a powerful strategy to enhance efficiency and stability of OSCs. With the rapid advances of interface layer materials and active layer materials, power conversion efficiencies (PCEs) of both single-junction and tandem OSCs have exceeded a landmark value of 10%. This review summarizes the latest advances in interfacial layers for single-junction and tandem OSCs. Electron or hole transporting materials, including metal oxides, polymers/small-molecules, metals and metal salts/complexes, carbon-based materials, organic-inorganic hybrids/composites, and other emerging materials, are systemically presented as cathode and anode interface layers for high performance OSCs. Meanwhile, incorporating these electron-transporting and hole-transporting layer materials as building blocks, a variety of interconnecting layers for conventional or inverted tandem OSCs are comprehensively discussed, along with their functions to bridge the difference between adjacent subcells. By analyzing the structure-property relationships of various interfacial materials, the important design rules for such materials towards high efficiency and stable OSCs are highlighted. Finally, we present a brief summary as well as some perspectives to help researchers understand the current challenges and opportunities in this emerging area of research.

Efficiency enhancement of organic photovoltaic devices by embedding uncapped Al nanoparticles in the hole transport layer

The effects of incorporating uncapped aluminum nanoparticles, fabricated by laser ablation in liquid, in the hole transport layer of organic photovoltaic devices were systematically investigated. Resulting in about 9% enhancement in the power conversion efficiency.