Optical Study and Experimental Realization of Nanostructured Back Reflectors with Reduced Parasitic Losses for Silicon Thin Film Solar Cells.

Zeyu Li,Pere Cabarrocas,Rusli E,Chenjin Lu,Wanghua Chen,Junkang Wang,Martin Foldyna,Ari Prakoso,Erik Johnson,Pavel Bulkin,Rasha Khoury

doi:10.3390/nano8080626

Abstract

We study light trapping and parasitic losses in hydrogenated amorphous silicon thin film solar cells fabricated by plasma-enhanced chemical vapor deposition on nanostructured back reflectors. The back reflectors are patterned using polystyrene assisted lithography. By using O2 plasma etching of the polystyrene spheres, we managed to fabricate hexagonal nanostructured back reflectors. With the help of rigorous modeling, we study the parasitic losses in different back reflectors, non-active layers, and last but not least the light enhancement effect in the silicon absorber layer. Moreover, simulation results have been checked against experimental data. We have demonstrated hexagonal nanostructured amorphous silicon thin film solar cells with a power conversion efficiency of 7.7% and around 34.7% enhancement of the short-circuit current density, compared with planar amorphous silicon thin film solar cells.

Highlights

By applying plasma-enhanced chemical vapor deposition (PECVD), hydrogenated amorphous/ microcrystalline silicon (a/μc-Si:H) tandem solar cells fabricated at low temperatures have been researched extensively over the last decade and have achieved over 14% stabilized efficiency [1]
We have demonstrated a novel hexagonal nanostructured design and fabrication process for light trapping in silicon thin film solar cells
The hexagonal nanostructured back reflectors and corresponding solar cells were modeled by the finite element method and verified against experimental data

Summary

Introduction

By applying plasma-enhanced chemical vapor deposition (PECVD), hydrogenated amorphous/ microcrystalline silicon (a/μc-Si:H) tandem solar cells fabricated at low temperatures (around 150 ◦C) have been researched extensively over the last decade and have achieved over 14% stabilized efficiency [1]. Nanostructured Ag/ZnO back reflector (BR) substrates are one of the most effective and process compatible approaches for an enhanced light trapping performance in silicon thin film solar cells. Random nanostructured ASAHI U type substrates with a r.m.s. roughness of around 35 nm are often used in silicon thin film solar cells to enhance light trapping [9]. For random Ag/ZnO BR parasitic losses estimation, extra experimental results are needed to set up an accurate BEMA model. We first systematically studied optical losses in flat Ag/ZnO BRs and random nanostructured Ag/ZnO ASAHI BRs. With different ZnO thickness as the extra variable, we assessed the simulation accuracy of the proposed BEMA model by experimental results.

Experimental Details

Results and Discussion

Bruggeman Effective Medium Approximation Simulation

Conclusions