Nanoscale imaging of photocurrent enhancement by resonator array photovoltaic coatings

Abstract

Nanoscale surface patterning commonly used to increase absorption of solar cells can adversely impact the open-circuit voltage due to increased surface area and recombination. Here, we demonstrate absorptivity and photocurrent enhancement using silicon dioxide (SiO2) nanosphere arrays on a gallium arsenide (GaAs) solar cell that do not require direct surface patterning. Due to the combined effects of thin-film interference and whispering gallery-like resonances within nanosphere arrays, there is more than 20 % enhancement in both absorptivity and photocurrent. To determine the effect of the resonance coupling between nanospheres, we perform a scanning photocurrent microscopy (SPCM) based on a near-field scanning optical microscopy (NSOM) measurement and find a substantial local photocurrent enhancement. The nanosphere-based antireflection coating (ARC), made by the Meyer rod rolling technique, is a scalable and a room-temperature process; and, can replace the conventional thin-film-based ARCs requiring expensive high-temperature vacuum deposition.

Quantum Dot Sensitized Whisperonic Solar Cells—Improving Efficiency Through Whispering Gallery Modes

“…Various strategies have been explored to address this issue, which include antireflection coating of dielectric thin films (Zhao et al, 1995) and surface patterning with nanocones (Zhu et al, 2009) and nanopyramids (Mavrokefalos et al, 2012), which gave tangible results. However, the increased surface area resulting from the patterned nanostructures cause an undesired recombination loss and thus decreases the open-circuit voltage, in turn limiting the power conversion efficiency (Ha et al, 2018). Significant enhancement in absorptivity without compromising the opencircuit voltage has been reported by texturing the surface with cellulose fibers, which gradually changes the refractive index from air to the active material.…”

“…The incident light is excited into resonant modes using spherical resonators and optically coupled to the absorbing medium. WGMs being mainly the surface modes, photonic whispering gallery excitation ultimately leads to enhanced light absorption within the high index active material of solar cells (Ha et al, 2018). A complete mechanism behind the efficiency enhancement through WGM is yet to be understood clearly.…”

“…From finite-difference time-domain (FDTD) simulations, it has been shown that power absorbed is directly proportional to the intensity of electric fields (Grandidier, 2012). Thus, the most commonly cited reasoning is the increase in electric field intensities arising from whispering gallery resonances at the interface between resonator array and the photosensitive material (Ha et al, 2018). Yin et al have shown the enhancement in the absorption of silicon by decorating optical whispering gallery resonators on the surface of Si solar cells (Yin et al, 2013).…”

“…Smaller spheres on the other hand are also proven to enhance the absorption as these spheres form an anti-reflection layer (Yin et al, 2016). Dielectric nanospheres decorated on the solar cells can gradually change the refractive index from air to the high index active material, thus favoring absorption enhancement (Ha et al, 2018). Recently, Ha et al have demonstrated nearly 20% enhancement in absorptivity and photocurrent using silicon dioxide (SiO 2 ) nanosphere arrays on a gallium arsenide (GaAs) solar cell.…”

Electrospun Nitrogen-doped TiO2 Nanofibrous Thin Film for Photovoltaic Application

“…Beside improving the chemical properties, increasing the surface area of TiO2 film layer improve the photocatalytic efficiency by absorbing high amount of sensitized dye that lead high amount of light harvesting [13]. Also, high surface area of TiO2 thin film allow electrolyte to diffuse through the cell intensively and results high photo electrochemical reaction rate.…”