We unveil new device physics and provide details of device mechanisms by investigating polymer solar cells (PSCs) incorporating Au nanoparticles (NPs) into the hole collection poly(3,4ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) layer. Theoretical and experimental results show that the very strong near field around Au NPs due to Localized Surface Plasmonic Resonance (LSPR) mainly distributes laterally along the PEDOT:PSS layer rather than vertically into the adjacent active layer, leading to minimal enhancement of light absorption in the active layer. This finding can be extended to a typical class of solar cells incorporating metallic NPs in spacing layers adjacent to the active layer. With optical effects proven to be minor contributors to device performance improvements, we investigate the electrical properties of the PSCs and obtain insights into the detailed device mechanisms. Improvements in power conversion efficiency (PCE) of solar cells are found to originate from the enlarged active layer/PEDOT:PSS interfacial area and improved PEDOT:PSS conductivity. At high NP concentrations, reduced exciton quenching at donor/acceptor junctions is found to cause PCE deterioration. Our findings indicate that it is highly important to investigate both optical and electrical effects for understanding and optimizing PSC performances.
The effects of Au nanoparticles (NPs) incorporated into the active layer of polymer solar cells (PSCs) with a newly synthesized donor polymer are investigated in detail. Our work shows that localized surface plasmonic resonance (LSPR) introduced by the metallic NPs can experimentally and theoretically enhance the light absorption in the active layer of PSCs because the strong LSPR near field mainly distributes laterally along the active layer. The understanding can be applied to other metallic NPs incorporated organic solar cells. Meanwhile, our results show that electrical properties can counter-diminish the optical enhancement from LSPR and thus reduces the overall performance improvement. It is important that both optical and electrical properties need to be studied and optimized simultaneously for achieving improved power conversion efficiency. The study contributes to better understanding on the uses of Au NPs for enhancing PSC performances.
ABSTRACT:We have investigated the effects of a directly patterned active layer together with silver nanograting arrays as the anode of inverted polymer solar cells (PSCs). The patterned nanostructure not only greatly enhances the light absorption of the active layer through both light diffraction and coupling to surface plasmon polariton (SPP) modes but also obviously promotes the fill factor of the patterned device. The absorption spectrum shows improvement over a broad wavelength range, especially around the 400 nm region and the near-infrared region surrounding 700 nm, which can also be reconfirmed from Incident Photon to Electron Conversion Efficiency (IPCE) and zeroth-order reflection spectra. Most importantly, our physical study shows that the absorption peak of 400 nm is due to the resonant waveguide mode, and the absorption peak of 700 nm is attributed to the excited SPP mode induced by the metallic back grating. Besides, another splitting SPP mode, called plasmonic band edge, around 800 nm is clarified from our detailed model. Consequently, on one hand, our work offers the fundamental physical understanding of plasmonic band edge resonances in periodic grating nanostructures for enhancing the optical absorption of thin-film photovoltaics. On the other hand, the study contributes to improving the power conversion efficiency of inverted PSCs by about 19% through incorporating grating structures that can be a potential candidate for improving the performances of other PSCs.
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