The versatile designs and optimizations for cylindrical TiO_2-based scatterers for solar cell anti-reflection coatings

Abstract

The anti-reflection coating(ARC) based on dielectric nano-particles has been recently proposed as a new way to achieve the low reflectance required for solar cell front surfaces. In this scenario, the Mie modes associated with the dielectric nano-particles are utilized to facilitate photon forward scattering. In this work, versatile designs together with systematically optimized geometry are examined, for the ARCs based on dielectric scatterers. It is found that the Si3N4-TiO2 or SiO2-TiO2 stack is capable of providing low reflectance while maintaining a flat and passivated ARC-semiconductor interface which can be beneficial for reduced interface recombination and prevent V(OC) degradation associated with topography on the active materials. It is also confirmed that the plasmonic nano-particles placed at the front side of solar cells is not a preferred scheme, even with thorough geometrical optimization. At the ultimate design based on mixed graded index(GI) Mie-scattering, the averaged reflectance can be as low as 0.25%. Such a low reflectance is currently only achievable by ultra-long silicon nano-tips, but silicon nano-tips introduce severe surface recombination. On the other hand, the mixed GI Mie design preserves a flat and passivated ARC-silicon interface, with total thickness reduced to 279.8 nm, much thinner than 1.6 μm for silicon nanotips. In addition, the light trapping capability of mixed GI Mie design is much better than silicon nanotips. In fact, when compared to the state-of-art TiO2 light trapping anti-reflection coating, the mixed GI Mie design provides same light trapping capability while providing much lower reflectance.

Nanoparticles for light management in ultrathin chalcopyrite solar cells

“…Benefits of dielectric nanosphere coatings have been revealed e.g., in GaAs and Si solar cells. Whispering gallery modes, 10 mixed graded index Mie-scattering 46 and focusing behavior 47 of nanoparticles have been identified to lead to enhanced incoupling of light. All these examples benefit from a close distance of the nanospheres to the absorber layer.…”

Sufficient condition for perfect antireflection by optical resonance at dielectric interface

“…In recent years, a new approach for antireflection has been proposed and widely adopted [29][30][31][32][33][34][35][36][37][38]. In this approach, one places arrays of nanoparticles at or near the air-dielectric interface ( Figure 1).…”

“…First, unlike the tapering geometry for the adiabatic impedance matching that is commonly done by etching into the active material, which may increase surface recombination, the resonant antireflection can be achieved by simply coating the surface with nanoparticles without an etching process [29,33,46]. Second, the optical resonances might in addition provide light trapping functionalities [33,[46][47][48][49][50][51][52], might enhance the broadband antireflection performance indirectly, for example, by influencing the material dispersion [53], and might allow tenability of the spectral range of antireflection [54].…”

Condition for perfect antireflection by optical resonance at material interface

“…In recent years, a new approach for antireflection has been proposed and widely adopted [24][25][26][27][28][29][30][31][32][33]. In this approach, one places arrays of nanoparticles at or near the air-dielectric interface ( Fig.…”

“…This approach has several unique potential beneficial characteristics compared to other approaches [36][37][38][39][40]. First, unlike the tapering geometry (for the adiabatic impedance matching) that is commonly done by etching into the active material, which may increase surface recombination, the resonant antireflection can be achieved by simply coating the surface with nanoparticles without an etching process [24,28,41]. Second, the optical resonances might in addition provide light trapping functionalities [28,[41][42][43][44][45][46][47], might enhance the broadband antireflection performance indirectly, for example, by influencing the material dispersion [48], and might allow tunability of the spectral range of antireflection [49].…”