Hägglund Carl, Apell S Peter
Department of Applied Physics, Chalmers University of Technology, Göteborg, Sweden.
Opt Express. 2010 Sep 13;18 Suppl 3:A343-56. doi: 10.1364/OE.18.00A343.
For ultrathin (~10 nm) nanocomposite films of plasmonic materials and semiconductors, the absorptance of normal incident light is typically limited to about 50%. However, through addition of a non-absorbing spacer with a highly reflective backside to such films, close to 100% absorptance can be achieved at a targeted wavelength. Here, a simple analytic model useful in the long wavelength limit is presented. It shows that the spectral response can largely be characterized in terms of two wavelengths, associated with the absorber layer itself and the reflective support, respectively. These parameters influence both absorptance peak position and shape. The model is employed to optimize the system towards broadband solar energy conversion, with the spectrally integrated plasmon induced semiconductor absorptance as a figure of merit. Geometries optimized in this regard are then evaluated in full finite element calculations which demonstrate conversion efficiencies of up to 64% of the Shockley-Queisser limit. This is achieved using only the equivalence of about 10 nanometer composite material, comprising Ag and a thin film solar cell layer of a-Si, CuInSe₂ or the organic semiconductor MDMO-PPV. A potential for very resource efficient solar energy conversion based on plasmonics is thus demonstrated.
对于等离子体材料和半导体的超薄（约10纳米）纳米复合薄膜，垂直入射光的吸收率通常限制在约50%。然而，通过在这类薄膜中添加具有高反射背面的非吸收性间隔层，在目标波长处可实现接近100%的吸收率。在此，提出了一个在长波长极限下有用的简单解析模型。它表明，光谱响应在很大程度上可以用两个波长来表征，分别与吸收层本身和反射支撑体相关。这些参数会影响吸收峰的位置和形状。该模型用于朝着宽带太阳能转换优化系统，将光谱积分的等离子体诱导半导体吸收率作为一个品质因数。然后在全有限元计算中评估在这方面优化的几何结构，计算结果表明转换效率高达肖克利-奎塞尔极限的64%。这仅使用约10纳米的复合材料等效物即可实现，该复合材料包括银以及非晶硅、铜铟硒₂或有机半导体MDMO-PPV的薄膜太阳能电池层。由此证明了基于等离子体激元的太阳能转换具有非常高效利用资源的潜力。
