Enhanced light-scattering properties of sputtered Ag/Al:Si bilayers deposited at a low substrate temperature – A potential back reflector for highly efficient flexible thin-film photovoltaic devices

• Published in: Solar energy materials and solar cells 2014-11, Vol.130, p.481-489
• Main Authors: Cho, Jun-Sik, Kim, Sol Ji, Choi, Bo-Hun, Ahn, Seung Kyu, Park, Joo Hyung
• Format: Article
• Language: English
• Subjects: Aluminum; Applied sciences; Back reflector; Deposition; Direct energy conversion and energy accumulation; Electrical engineering. Electrical power engineering; Electrical power engineering; Energy; Exact sciences and technology; Grain growth; Light scattering; Nanostructure; Natural energy; Photoelectric conversion; Photovoltaic cells; Photovoltaic conversion; Reflectors; Silver; Solar cells; Solar cells. Photoelectrochemical cells; Solar energy; Surface texturing; Texture; Thin films; Thin-film solar cell
• ISSN: 0927-0248; 1879-3398
• DOI: 10.1016/j.solmat.2014.07.049

Nanotextured Ag/Al:Si back reflectors with enhanced light-scattering efficiency for flexible thin-film solar cells were developed at a low substrate temperature (Ts) by sophisticated control of the microstructural evolution of metal films. Development was based on a structure zone model and a bilayer concept involving a high reflectivity Ag top layer deposited onto a surface-textured Al:Si bottom layer. The texture evolution with a root-mean-square (σrms) surface roughness of 60.1nm in the Al:Si bottom layer was successfully achieved at a low Ts of 100°C by abnormal grain growth. The growth was induced by the low melting point of Al and the impurity drag effect on the grain boundaries caused by the Si dopant, whereas the σrms of the pure Ag film deposited at Ts=200°C was 46.9nm. After room temperature deposition of highly reflective Ag films onto the nanotextured Al:Si bottom layers, significant improvement in the light-scattering properties of the Ag/Al:Si bilayers was obtained compared to the Al:Si films without Ag films, for which the reflection significantly decreased due to the interband absorption and low reflectivity of Al. Under optimum conditions, the light-scattering efficiency of nanotextured Ag/Al:Si bilayers deposited at Ts=75°C is comparable to that of reference Ag films at Ts=200°C. When the nanotextured Ag/Al:Si bilayers deposited at Ts=75°C as back reflectors were applied to flexible nc-Si:H thin-film solar cells, a high conversion efficiency of 8.6% was successfully achieved, and no detrimental reduction in cell performance was observed in comparison with the solar cell using the reference Ag back reflectors deposited at 200°C. [Display omitted] •Nanotextured Ag/Al:Si bilayers were prepared at low substrate temperature.•High texture-evolution was achieved in the Al:Si films by abnormal grain growth.•Enhanced light-scattering properties were obtained in the nanotextured bilayers.