Light trapping in planar ultrathin-film solar cells is limited due to a small number of optical modes available in the thin-film slab. A nanostructured thin-film design could surpass this limit by providing broadband increase in the local density of states in a subwavelength volume and maintaining efficient coupling of light. Here we report a broadband metasurface design, enabling efficient and broadband absorption enhancement by direct coupling of incoming light to resonant modes of subwavelengthscale Mie nanoresonators defined in the thin-film active layer. Absorption was investigated both theoretically and experimentally in prototypes consisting of lithographically patterned, two-dimensional periodic arrays of silicon nanoresonators on silica substrates. A crossed trapezoid resonator shape of rectangular cross section is used to excite broadband Mie resonances across visible and near-IR spectra. Our numerical simulations, optical absorption measurements and photocurrent spectral response measurements demonstrate that crossed trapezoidal Mie resonant structures enable angle-insensitive, broadband absorption. A short circuit current density of 12.0 mA/cm2 is achieved in 210 nm thick patterned Si films, yielding a 4-fold increase compared to planar films of the same thickness. It is suggested that silicon metasurfaces with Mie resonator arrays can provide useful insights to guide future ultrathin-film solar cell designs incorporating nanostructured thin active layers.
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机译:平面超薄膜太阳能电池中的光捕获受到限制,这是因为薄膜平板中的光学模式很少。纳米结构的薄膜设计可以通过在亚波长体积中提供局部态密度的宽带增加并保持光的有效耦合来超越此限制。在这里,我们报告了一种宽带超表面设计,该技术通过将入射光直接耦合到薄膜有源层中定义的亚波长尺度Mie纳米谐振器的谐振模式来实现有效和宽带吸收增强。在原型上对吸收进行了理论和实验研究,该原型由光刻图案化的二氧化硅纳米谐振器在二氧化硅衬底上的二维周期性阵列组成。矩形横截面的交叉梯形谐振器形状用于激发可见光和近红外光谱的宽带Mie谐振。我们的数值模拟,光学吸收测量和光电流光谱响应测量表明,交叉的梯形Mie谐振结构可实现对角度不敏感的宽带吸收。在210 nm厚的图案化Si膜中,短路电流密度达到12.0 mA / cm 2 sup>,与相同厚度的平面膜相比,其短路电流密度提高了4倍。提出具有Mie谐振器阵列的硅超表面可以提供有用的见识,以指导未来结合纳米结构薄有源层的超薄膜太阳能电池设计。
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