Tandem solar cells offer avenues to increase efficiency beyond the current state of the art for commercial photovoltaics. New absorbers and device structures including hybrids that combine different material classes such as III-V/Si or perovskite/Si are intensely researched. To guide the evolution of tandem solar cells towards commercialization, accurate measurements of performance are required. In this tutorial we will discuss how an accurate performance calibration for a tandem cell or module is done and present common measurement artifacts and methods to identify and avoid them.
Authors / Speakers: Gerald Siefer | Fraunhofer ISE & Nikos Kopidakis | NREL
While the accurate measurement of the perormance of a tandem solar cell or module has special requirements, it still builds on the methods used for single-junction cells. The tutorial will start by presenting the fundamentals of solar cell calibration, including definitions of spectral and total irradiance, spectral response of the cell and measurement of the area. We will then discuss the meaning of the spectral correction factor for current-voltage (IV) measurements of single-junction solar cells. In this part we will also discuss how the actual measurement process needs to be adapted to metastable and slow responding devices.
The second part of the tutorial will start by introducing different structures of tandem solar cells, including the more commonly used 2-terminal (2T) and 4-terminal (4T) structures, and the more recently proposed and demonstrated 3-terminal (3T) cells.
We will then discuss the special requirements that these structures pose for measuremnet of the spectral response of each subcell, and how the spectral correction method discussed in the introduction needs to be modified for tandem cells. We will put a focus on the pitfalls that can occur during these measurements. In the case of QE measurements, this concerns in particular the difficulties in determining the absolute QE as well as the occurrence of QE artifacts, whose detection, cause and correction we will briefly describe. We will then present the various spectral correction procedures for the IV measurement, all of which aim to adjust the spectrum of the solar simulation in a way taht each sub-cell generates the same current as it would under the standard spectrum. The effects and measurement uncertainties that arise if this is not achieved are then discussed.
In the final part of the tutorial we will show how the above procedures can be adapted to modules with tandem cells. In addition to the possibility of using natural sunlight, we will also demonstrate how the full calibration of such modules can be achieved indoors with large-area, spectrally adjustable solar simulators including the determination of the QE on module level.
Authors / Speakers: Gerald Siefer | Fraunhofer ISE & Nikos Kopidakis | NREL
While the accurate measurement of the perormance of a tandem solar cell or module has special requirements, it still builds on the methods used for single-junction cells. The tutorial will start by presenting the fundamentals of solar cell calibration, including definitions of spectral and total irradiance, spectral response of the cell and measurement of the area. We will then discuss the meaning of the spectral correction factor for current-voltage (IV) measurements of single-junction solar cells. In this part we will also discuss how the actual measurement process needs to be adapted to metastable and slow responding devices.
The second part of the tutorial will start by introducing different structures of tandem solar cells, including the more commonly used 2-terminal (2T) and 4-terminal (4T) structures, and the more recently proposed and demonstrated 3-terminal (3T) cells.
We will then discuss the special requirements that these structures pose for measuremnet of the spectral response of each subcell, and how the spectral correction method discussed in the introduction needs to be modified for tandem cells. We will put a focus on the pitfalls that can occur during these measurements. In the case of QE measurements, this concerns in particular the difficulties in determining the absolute QE as well as the occurrence of QE artifacts, whose detection, cause and correction we will briefly describe. We will then present the various spectral correction procedures for the IV measurement, all of which aim to adjust the spectrum of the solar simulation in a way taht each sub-cell generates the same current as it would under the standard spectrum. The effects and measurement uncertainties that arise if this is not achieved are then discussed.
In the final part of the tutorial we will show how the above procedures can be adapted to modules with tandem cells. In addition to the possibility of using natural sunlight, we will also demonstrate how the full calibration of such modules can be achieved indoors with large-area, spectrally adjustable solar simulators including the determination of the QE on module level.
