Antonius R. Burgers

Ribbon Growth on Substrate and Molded Wafer-Two Low Cost Silicon Ribbon Materials for PV

This paper focuses on two very promising silicon ribbon materials currently produced for research: ribbon growth on substrate (RGS) by ECN solar energy and molded wafer (MW) by GE Energy. Both materials are investigated in terms of solar cell processing and characterisation. First cell results of large area 10times10 cm2 RGS cells are presented as well as results from 5times5 cm2 cells processed from 8times12 cm2 RGS and 12.5times12.5 cm2 MW wafers

Screen-printed ribbon growth on substrate solar cells approaching 12% efficiency

Ribbon growth on substrate (RGS) solar cells have been processed at the University of Konstanz using an adapted industrial-type fire-through SiN process. An efficiency of 12.3% has been reached on a 5/spl times/5 cm/sup 2/ cell. This is the highest efficiency obtained on this very promising and cost-effective material using an industrial-type cell process. An important factor for the increase in efficiency was the reduced oxygen concentration of almost an order of magnitude in the current RGS wafer material compared to former RGS material. Enhanced J/sub sc/, V/sub oc/ and L/sub eff/ values in the range of 100 /spl mu/m as well as lifetimes above 4 /spl mu/s demonstrate the potential of the new low oxygen RGS material. Efficiencies well above 13% should be possible, provided a surface texture is applied and shunting mechanism can be avoided.

Kinetics of hydrogenation and interaction with oxygen in crystalline silicon

Sufficient passivation of recombination active defects in the bulk of crystalline silicon solar cells using atomic hydrogen is a key feature for reaching high conversion efficiencies. This is of special interest for promising low-cost multi-crystalline (mc) materials, as a substantial cost reduction concerning Watt-peak(Wp)-costs seems to be possible. The effectiveness of this hydrogenation is strongly influenced by the diffusion kinetics of atomic hydrogen in silicon. Oxygen impurities seem to play a major role, as they have the ability to trap hydrogen, slowing down the diffusion of hydrogen atoms. For two crystalline silicon materials the influence of different oxygen concentrations on hydrogen kinetics is discussed. We demonstrate that not only the overall oxygen concentration, but as well the thermal history of the samples has to be taken into account. Precipitation of oxygen alters the diffusion kinetics and has an influence on vacancy concentration. Faster passivation of crystal defects can be reached in low-oxygen samples.

ECN n-type silicon solar cell technology: An industrial process that yields 18.5%

There is currently much interest in n-type solar cells because of the advantages of this material. N-type material is expected to be more favourable for obtaining high efficiencies than p-type doped substrates. We have developed a process for n-type solar cells for large area multicrystalline and monocrystalline silicon wafers. The production process is based on industrial processing steps such as screen-printed metallization and firing through. The surfaces of these cells are passivated with a layer stack consisting of SiO 2 and SiN x where the former is created by a wet chemical process and the latter by inline PECVD. We demonstrate that the surface passivation can be improved with an alternative wet chemical process for creating the SiO 2 layer. This new process results in an enhancement of the implied V oc of unmetallized cells as measured by quasi-steady-state photoconductance (QSSPC) and the V oc of completed cells. The process Improvements have yielded a new record efficiency of 18.5 % (for a particular rear reflection surface) that was independently confirmed by Fraunhofer ISE CalLab.

Designing IBC cells with FFE: Long range effects with circuit simulation

IBC cells with Front Floating Emitter (FFE) pose different design challenges compared to more conventional IBC cells with FSF (Front Surface Field). The FFE enables hole transport over distances that are large compared to the typical BSF or emitter width. The core of the cell design is commonly a device simulation in which, because of the computer resources involved, typically one simulates an as small as possible, but representative part of the solar cell. In an IBC cell this corresponds to 1/2 of the BSF and 1/2 of the emitter. Such a unit cell does not account for important geometric features, such as busbars and pads, edges or interruptions in metallization fingers. We show how to construct an equivalent circuit for our Mercury FFE IBC cells to model features beyond the unit cell efficiently, taking into account the lateral hole transport in the FFE. We compare and calibrate the circuit model against device simulations with quokka.