Abstract
Here, we review recent progress on the integration of plasmonic electrodes into bulk-heterojunction organic photovoltaic devices. Plasmonic electrodes, consisting of thin films of metallic nanostructures, can exhibit a number of optical, electrical, and morphological effects that can be exploited to improve performance parameters of ultrathin photovoltaic active layers. We review the various types of plasmonic electrodes that have been incorporated into organic photovoltaics such as nanohole, nanowire, and nanoparticle arrays and grating electrodes and their impact on various device performance parameters. The use of plasmonic back electrodes can impact device performance in a number of ways because the mechanisms of performance improvements are often a complex combination of optical, electrical, and structural effects. Inverted bulk heterojunction device architectures have been shown to benefit from the multifunctionality of plasmonic back electrodes as they can minimize space-charge effects and reduce hole carrier collection lengths in addition to providing improved light localization in the active layer. The use of semi-transparent plasmonic electrodes can also be beneficial for organic photovoltaics as they can exhibit a variety of optical properties such as light scattering, light localization, extraordinary transmission of light, and absorption-induced transparency, in addition to providing an alternative to metal oxide–based transparent electrodes.
Highlights
Downloaded From: https://www.spiedigitallibrary.org/journals/Journal-of-Photonics-for-Energy on 07 Feb 2022 Terms of Use: https://www.spiedigitallibrary.org/terms-of-use devices and is challenging to predict using optical simulations alone. This highlights the need for more extensive external quantum efficiency (EQE) studies of bulk-heterojunction organic photovoltaic (BHJ-OPV) devices incorporating plasmonic electrodes because optical/photonic effects may not be the only cause of enhancements in solar power conversion efficiency
Nanosphere lithography has typically been used to fabricate ordered arrays of nanotriangles on a PEDOT:PSS-soldered Ag nanowires (PEDOT):PSS-coated ITO layer,[172,173] and solution-based Ag nanowires (AgNWs) have been used between the PEDOT:PSS and the P3HT:PCBM layers, leading to a 1.18 enhancement factor in the efficiency of conventional devices incorporating these types of plasmonic interlayers.[51]
A variety of different plasmonic, photonic and plasmonic-photonic hybrid modes supported by plasmonic electrodes have been demonstrated to contribute to improved bulk-heterojunction organic photovoltaic (BHJ-OPV) device performance through increased light trapping and active-layer absorption enhancement
Summary
Surface plasmon resonances that exist on the surface of highly conductive, nanostructured metals have been shown to be of benefit to thin-film, inorganic photovoltaics[1,2,3,4,5,6,7,8,9] as well as organic photovoltaics.[10,11,12,13,14,15] Metals that are efficiently able to support surface plasmons in the visible regime (e.g., Ag, Cu, and Au) tend to have high work functions (either for the pure metal or with a native surface oxide), making them suitable anodes for inverted bulk-heterojunction organic photovoltaics (BHJ-OPVs) due to their more stable anodic behavior (see Fig. 1).[16,17] In this paper, we will review recent work on the incorporation of plasmonic electrodes, which are metal electrodes composed of an array of metallic nanostructures, into BHJ-OPV devices, with an emphasis on the inverted architecture. Front electrodes of a photovoltaic device are proposed to potentially enhance the performance of inverted BHJ-OPVs through light trapping or localization in the thin-film active layer.[1,2,5,12,14,15] In addition to light management, plasmonic electrodes may be suitable replacements for transparent conducting electrodes when employed as the front electrode of the device. Petoukhoff et al.: Plasmonic electrodes for bulk-heterojunction organic photovoltaics plasmon polaritons, SPPs).[1,2,28] In the case of a discrete metallic nanoparticle (NP), the oscillating electric field associated with light can displace the sea of electrons on the surface of the metal, forming an electric dipole on the metal [Fig. 2(a)].1,2,28. We will discuss the performance of plasmonic electrodes incorporated into BHJ-OPV devices in each of these configurations, as well as the optical, electrical, and morphological effects associated with them
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