Dirk Habermann

High Efficiency Multi-busbar Solar Cells and Modules

In this paper, a detailed overview of multi-busbar solar cells and modules with selective emitter, a fine line screen printed front side metallization, and full aluminum rear side are presented. The designs of three-busbar and multi-busbar solar cells and modules are compared and assessed by solar cell, module performance, and Ag metal consumption. Assembled multi-busbar solar cells and four-cell modules are compared with industrial type three-busbar solar cells and modules that demonstrate average fill factor gains of 0.6%abs on the module level. A reduction in Ag paste consumption of about 50%abs for the front grid is achieved using the multi-busbar front electrode design with a fine line screen printing process. An advanced front side metallization technique using an Ag seed and Ag LIP approach demonstrates the potential to further reduce Ag consumption to values as low as 32 mg/cell.

Investigation of the Internal Back Reflectance of Rear-Side Dielectric Stacks for c-Si Solar Cells

This paper addresses the calculation of internal back reflectance for various dielectrics that are used in rear-side passivated crystalline silicon solar cells. Optical modeling of various stack configurations is examined to explore the back-surface reflectance at the Si-dielectric interface for different film combinations and thicknesses as a function of wavelength and internal angle of incidence at the rear side. Specifically, configurations using aluminum oxide (AlOx), silicon nitride (SiNx), titanium dioxide (TiO2), and silicon dioxide (SiO2) were investigated with a focus on designing stack configurations that will also allow for high-quality passivation and are compatible with a high-volume manufacturing environment. In addition, samples were fabricated by plasma-enhanced and atmospheric pressure chemical vapor deposition of thin dielectric films onto polished and textured monocrystalline silicon wafers. Spectral reflectance curves of the samples are presented to supplement and validate the conclusions that are obtained from the optical modeling data.

Tailoring the Optical Properties of APCVD Titanium Oxide Films for All-Oxide Multilayer Antireflection Coatings

In this paper, the optical properties and microstructure of titanium oxide (TiOx) thin films deposited by in-line atmospheric pressure chemical vapor deposition (APCVD) are tailored to act as effective antireflection coatings (ARCs) in crystalline silicon solar cells. The ability to control the crystalline phase, microstructure, and optical properties of these TiOx films by varying the deposition conditions is demonstrated. Because the refractive index of TiOx can be widely varied by changing the deposition temperature, these films can be applied as single- or double-layer ARCs (DLARCs) in crystalline silicon solar cells featuring a thin front-side passivation layer (e.g., thermal silicon oxide, aluminum oxide) or as a rear-side capping layer in rear passivated cells. Reflectance measurements on oxide-based DLARCs deposited on anisotropically textured monocrystalline Si wafers are presented for unencapsulated samples, along with the modeled performance of similar structures encapsulated in ethylene-vinyl acetate under varying angles of incidence. In the experiments on unencapsulated samples, two of the oxide-based DLARCs outperform a standard SiNx ARC, and all four outperform the SiNx ARC when encapsulated.

Optical modeling of the internal back reflectance of various c-Si dielectric stacks featuring AlO x , SiN x , TiO 2 and SiO 2

One promising path to a reduced cost of crystalline silicon (c-Si) photovoltaics (PV) is to increase silicon usage efficiency by using thinner wafers. Many challenges arise when transitioning to thin wafer cells, including increased surface recombination at the rear side of the cell, increased wafer bowing, and a reduction in optical absorption due to a decreased optical path length within the silicon. Rear side passivation provides great promise in addressing these challenges. This paper addresses rear side dielectric configurations that can optimize back surface reflectance, in addition to providing excellent surface passivation. Optical modeling of various stack configurations is examined to explore the back surface reflectance at the Si-dielectric interface for different film combinations and thicknesses as a function of wavelength and internal angle of incidence. Specifically, configurations using aluminum oxide (AlOx), silicon nitride (SiNx), titanium dioxide (TiO2), and silicon dioxide (SiO2) were investigated with a focus on designing stack configurations that will also allow for high quality passivation and are compatible with a high-volume manufacturing environment.