Advanced electrical simulation of thin film solar cells

Advanced electrical simulation of copper indium gallium diselenide solar cells is illustrated by setting up a demonstration case in SCAPS (Solar Cell Capacitance Simulator), the solar cell simulation programme of the University of Gent. The model includes band gap grading, multivalent defects and metastable transitions between defects. This simplified demonstration model clearly and quantitatively illustrates some topics that were extensively discussed in recent literature: metastable defects exist in either an acceptor or in a donor configuration; the occupation of these configurations is set during initial conditions at higher temperature, and then frozen in during cell operation at lower temperature. These occupations can strongly influence the effective doping profile in the absorber, and hence possible energy barriers in the structure. The dependence of such barriers on the initial conditions and on the operating voltage can cause a considerable dependence of the current–voltage characteristics on the initial conditions, especially of the fill factor. At the same time, the demonstration model illustrates some of the recent extensions of SCAPS.

► SCAPS, the Solar Cell Capacitance Simulator of UGent is freely available.
► SCAPS is keeping up with the sophistication of state-of-the-art solar cells.
► It can now handle: multivalent and metastable defects; grading of all properties.
► It is shown how metastable defects can lead to metastable cell characteristics.
► A relation conduction band barrier-fill factor is numerically established.