Light-trapping structures

Figure 4.6 shows a light-trapping structure for a thin him, where reflection from the rear surface is also caused by total internal reflection. 

Abstract In solar applications microstructured polymer surfaces can be used as optically functional devices. Examples are antireflective surfaces, dayUghting, sun protection systems, concentrator photovoltaic modules and light trapping structures in organic solar cells. The examples and the principles of function of the respective microstmctures are described in detail. The suitability of different manufacturing methods is discussed. Two of them, ultraprecision machining and interference lithography are described. For the latter experimental results are shown. Finally, the opportunities and the risks of the shown approaches are discussed. 

A very old and obvious solution is to deposit a dielectric layer onto metal, thus reducing the absorptance and increasing reflectance. The transmittance remains very low or zero in such structures, but this fact is of no consequence for light trapping structures for photodetectors. 

C. Wang, S. Yu, W. Chen, C. Sun, Highly efficient light-trapping structure design inspired by natural evolution. Sci. Rep. 3, 1025 (2013)... 

The second equihbrium group encompasses strucmres for increase in the optical path of the beam which already entered the active area of the detector, the so-called light trapping structures. These structures simultaneously increase radiative lifetime through the mechanism of reabsorption—photon recycling. They include different surface rehef stmctures for the increase in total internal reflection, from diflractive to macroscopic ones. Reflective detector surfaces also belong to this group, both the back-side ones and fuU resonant cavities (RCE—resonant cavity enhancement) with reflective surfaces both of the front and the back side of the detector. The most advanced stmctures for optical path and radiative time increase are radiative shields and photonic crystal enhancement stmcmres, which represent a fuU cavity enhancement and may support the existence of multiple modes. 

Fig. 1 Buried contact solar cell structure, an important wafer-based commercial silicon cell technology. Features include surface texturing for light trapping, diffusions front and rear and the front current grid buried in laser grooves. (Courtesy of UNSW Centre for Photovoltaic Engineering Image Library.)...

Apart from anti-reflective applications, interference lithography has also been used to originate structures for light management (diffusers, microlenses, microprism arrays) in buildings and display applications for light trapping in solar cells and for artificial Lotus Effect structures. ... 

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