Theoretical Modelling

© Fraunhofer ISE

Calculation of the optimum bandgaps for the top and middle cells of a triple-junction solar cell with a Ge bottom cell.

© Fraunhofer ISE

Simulated generation profile of a GaAs single-junction solar cell.

III-V multi-junction solar cells are extremely complex structures. Numerical simulations therefore serve to rapidly accelerate the development process. We employ a variety of simulation tools to analyze and optimize our solar cell structures.

In order to estimate the efficiency potential of new solar cell concepts, Fraunhofer ISE uses the etaOpt program developed in house, which is available for download here. This program permits researchers to determine the ideal band gap combination for different numbers of sub-cells, temperatures and reference spectra. An extension to the model also allows them to analyze the influence of spectral fluctuations at various locations over the course of a day or year.

Semiconductor layer structures are modeled using either a program called PVObjects or the Sentaurus TCAD tool from Synopsys. The resulting 2D simulation specifically includes the physical phenomena that are important to modeling III-V solar cells: optical interference, the generation and recombination of charge carriers, charge carrier transport to heterojunctions, tunneling processes and photon recycling. These simulation tools thus enable detailed analysis and realistic optimizations to be carried out for solar cell semiconductor layers.

In order to optimize the front side contact structure and current flow within an entire solar cell, network models are used whereby the solar cell is modeled as a network of electrical components.

Selected publications on this topic (Fraunhofer-Publica database)