Solar cell
Modeling of Electronic Properties of Interfaces in Solar Cells

<--  Principle of solar cells: photons generate electron-hole pairs, electrons/holes move to the contacts. The aim consists in minimizing the recombination losses.

Coworker: A. Glitzky, A. Mielke, M. Liero, M. Thomas
Cooperation: Institut für Helmholtz Zentrum für Materialien und Energie, Group SE1 Silizium-Photovoltaik
PVcomB ( Photovoltaics Competence Center Berlin)
ODERSUN AG Berlin - Frankfurt (Oder) - London
Period: June 2010 - May 2014
Support: DFG Research Center MATHEON Mathematics for key technologies: Modelling, simulation, and optimization of real-world processes, Project D22


Photovoltaic cells are built from layers of different materials. In thin-film solar cells, where rough interfaces are used for light trapping, the interfaces have a strong impact on the functionality of the device. Nanoscale-treatment of interfaces like doping near the interface or deposition of atoms into the interface is used to tune the electronic properties. Solar cells built from layers of amorphous and crystalline silicon (a-Si:H/c-Si) are investigated by our partners at the Helmholtz-Zentrum Berlin für Materialien und Energie (HZB). The key issues for enhancing the efficiency are the reduction of recombination losses at the a-Si:H/c-Si interface and the improvement of the charge-carrier transport over the heterointerface.
The bulk equations are drift-diffusion models for the charge carriers coupled with ODEs for immobile defects, which may absorb electrons or holes. The light, generating electron-hole pairs, is treated as a given source term. While the equations in the bulk are well established, the modeling of the kinetics of defects on transition layers and at interfaces is a topic of current research in the physics community. The band offsets at the interface and the non-vanishing state density in the a-Si:H mobility gap provide complications, e.g. tunneling of electrons from c-Si layers into defect states with energy levels inside the band gap of a-Si layers.
So far, there is no mathematical theory for special interface conditions. For heterogeneous materials always the classical interface conditions are used, like continuity of fluxes and chemical potentials.
The aim of the project is to find adequate models for the electronic properties of solar cells including interface kinetics, to investigate their analytical properties, to derive suitable numerical approximation schemes, and to provide simulation results.

Preparatory work