Flexible Silver Nanowire Meshes for High-Efficiency Microtextured Organic-Silicon Hybrid Photovoltaics

Abstract

Hybrid organic-silicon heterojunction solar cells promise a significant reduction on fabrication costs by avoiding energy-intensive processes. However, their scalability remains challenging without a low-cost transparent electrode. In this work, we present solution-processed silver-nanowire meshes that uniformly cover the microtextured surface of hybrid heterojunction solar cells to enable efficient carrier collection for large device area. We systematically compare the characteristics and device performance with long and short nanowires with an average length/diameter of 30 μm/115 nm and 15 μm/45 nm, respectively, to those with silver metal grids. A remarkable power conversion efficiency of 10.1% is achieved with a device area of 1 × 1 cm 2 under 100 mW/cm 2 of AM1.5G illumination for the hybrid solar cells employing long wires, which represents an enhancement factor of up to 36.5% compared to the metal grid counterpart. The high-quality nanowire network displays an excellent spatial uniformity of photocurrent generation via distributed nanowire meshes and low dependence on efficient charge transport under a high lightinjection condition with increased device area. The capability of silver nanowires as flexible transparent electrodes presents a great opportunity to accelerate the mass deployment of high-efficiency hybrid silicon photovoltaics via simple and rapid soluble processes. KEYWORDS: silver nanowire, solution process, conductive polymer, photovoltaics P hotovoltaic technology is playing an increasingly important role in electricity generation because of rising concerns with petroleum scarcity and green-house gas emissions. Nowadays, crystalline-silicon photovoltaics have a dominant market share for their high efficiency, environmental friendliness, and abundant material supply. 1 However, their energy payback time is still much longer than other thin-film-based technologies, 2 which is largely ascribed to the wafer cost and energy-intensive fabrication processes, such as furnace diffusion (900°C), electrode cofiring (900°C), and high-vacuum chemical deposition (400°C). Consequently, hybrid organic/ silicon solar cells have become an attractive approach in which the device combines the advantages of rapid wet-chemical processes with organic materials and wide absorption range with silicon for the heterojunction formation. 3−7 Among the multiple emerging organic materials, hybrid solar cells based on conductive polymer poly(3,4-ethylenedioxy-thiophene):poly-(styrenesulfonate) (PEDOT:PSS) directly spun-cast on planar or nanostructured silicon surfaces exhibit the most promising performance with a power conversion efficiency (PCE) of approximately 10%. 8−12 A validated device model has further projected that an ultimate efficiency of over 20% is possible with the band alignment of PEDOT:PSS and silicon by controlling interface states, surface reflection, and other factors. 13 Nevertheless, efficient carrier collection presents one of the bottlenecks for the scalability of hybrid devices because of...

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