Screen printed metal contacts to Si solar cells — Formation and synergistic improvements
Silicon solar cell technology has advanced by improvements to all aspects of cell design including metallization. Improvements to metal contacts have been synergistic with other cell improvements such as passivation, lightly doped emitters, and boron doped emitters. This paper briefly recounts the history of c-Si PV metallization technology and its synergy with other cell technologies. It concludes with a perspective on various metal contact mechanisms.
Microstructural characterization of front-side Ag contact of crystalline Si solar cells with lightly doped emitter
Crystalline Si (c-Si) solar cell production has reached an annual scale of ~20 GW globally. Development of this leading technology has been boosted by continuous innovation in material science and reduced material and processing costs. An example of such innovation is the step-wise progression to more lightly doped emitters (LDE) that reduces recombination in the solar cell. Continuous improvement in front-side (FS) metallization pastes has enabled this progression to lower series resistance and higher cell efficiency. We report here homogeneous emitter LDE cells with efficiencies as high as 18.9%, printed with advanced FS Ag paste. A clear understanding of the microstructure of the interfacial region between Ag contact and Si emitter, and the associated electrical conduction mechanism of LDE cells can provide the guidance needed to drive overall efficiency higher and end-user cost lower. We report our latest investigation of the microstructure of the interface between FS Ag contact and lightly-doped emitter using scanning electron microscopy techniques. The microstructural features such as nano-Ag colloids, interfacial glass, and Ag crystallites are studied in detail. The relationship between microstructure, cell performance, and current conduction mechanism for LDE cells are discussed.
The microscale obstacle-resolving meteorological model MITRAS v2.0: model theory
Abstract. This paper describes the developing theory and underlying
processes of the microscale obstacle-resolving model MITRAS version 2. MITRAS
calculates wind, temperature, humidity, and precipitation fields, as well as
transport within the obstacle layer using Reynolds averaging. It explicitly
resolves obstacles, including buildings and overhanging obstacles, to
consider their aerodynamic and thermodynamic effects. Buildings are
represented by impermeable grid cells at the building positions so that the
wind speed vanishes in these grid cells. Wall functions are used to calculate
appropriate turbulent fluxes. Most exchange processes at the obstacle
surfaces are considered in MITRAS, including turbulent and radiative
processes, in order to obtain an accurate surface temperature. MITRAS is also
able to simulate the effect of wind turbines. They are parameterized using
the actuator-disk concept to account for the reduction in wind speed. The
turbulence generation in the wake of a wind turbine is parameterized by
adding an additional part to the turbulence mechanical production term in the
turbulent kinetic energy equation. Effects of trees are considered
explicitly, including the wind speed reduction, turbulence production, and
dissipation due to drag forces from plant foliage elements, as well as the
radiation absorption and shading. The paper provides not only
documentation of the model dynamics and numerical framework but also a solid
foundation for future microscale model extensions.
