KAUST researchers have conducted outdoor tests, that have shown that an increase in temperature affects the performance of a tandem perovskite/silicon solar cell due to voltage losses aw well as current mismatch between the two sub-cells.
The energy yield of two-terminal tandem cells is maximized when the two sub-cells produce the same current at the maximum power point. However, when one of the two devices generates less current than the other, and current mismatch between the sub-cells occurs, the overall device's current is affected.
The KAUST team tested an encapsulated device (tandem cell) in hot and sunny climate and, with the help of meteorological data, they simulated the device's temperature over an entire year. These measurements showed, according to the team, that the cell performance is not only affected by voltage losses, as in other kinds of solar cells, but also by the aforementioned current mismatch.
Reducing the bandgap of the perovskite sub-cell is pointed out as a possible way to reduce the impact of temperature on this type of tandem cells. Ideal bandgaps should be lower than 1.65 electronvolts.
Also, this study reports the temperature coefficient of the industry viable perovskite/silicon tandem solar cells as -0.26% K-1 on double-side textured silicon wafers (with record certified current density of 19.8 mA/cm2). This temperature coefficient value is very close to the silicon heterojunction solar cells (-0.23 % K-1).
The KAUST team is currently working on the scaling-up of perovskite/silicon tandem solar cells targeting power conversion efficiency values beyond the limits of the single-junction solar cells.