Researchers at the Fraunhofer Institute for Solar Energy Systems (ISE) and the University of Freiburg have developed a purely electrical method that measures the individual subcell currents of perovskite-silicon tandem solar cells within milliseconds, using only the current-voltage (j-V) test equipment already in place on production lines.
Keeping the perovskite top cell and silicon bottom cell current-matched is critical to tandem yield and energy output, but the top cell is sensitive to processing and environmental drift, so its current can't be assumed stable across a production run. Until now, resolving each subcell's current has meant spectrometric characterization - recording j-V curves under multiple defined spectral conditions - which the team says can take more than an hour per device and is incompatible with production-line cycle times. The new method instead exploits a lifetime asymmetry between the two subcells: silicon, an indirect semiconductor, retains a millisecond-scale capacitive charge reservoir, while the perovskite's radiative recombination decays on a microsecond scale. Preconditioning the device near open-circuit voltage charges that silicon reservoir; a fast voltage step then triggers a current overshoot with two distinct plateaus - an initial one reflecting the perovskite subcell's current, followed by a drop to the silicon subcell's current once the reservoir depletes. Because the technique rides on a standard reverse j-V scan, integrating it into existing inline testers requires only a firmware-level adjustment, with no added hardware, light sources, or spectral filters.
The team validated the approach with Sentaurus TCAD simulations, an in-house 4 cm² tandem cell, and an encapsulated full-size industrial tandem cell in M6 format (166 mm × 166 mm). Reverse j-V scans of 7–12 milliseconds produced two clear current plateaus that quantitatively matched the subcell currents obtained from conventional spectrometric characterization of the same device, and repeated scans over multiple days showed a relative standard deviation below 0.1%.
The method applies directly when the silicon subcell is current-limiting - the standard design choice in industrial tandems, chosen to support bifaciality and reverse-bias protection - enabling real-time statistical process control that can catch drift in perovskite deposition or the optical stack before it causes yield loss.
In the perovskite-limited case, only a single plateau appears, which the authors note still flags that the perovskite subcell has become current-limiting, even though it doesn't yield a quantitative silicon-subcell value in that regime. The authors add that the underlying principle of exploiting the lifetime asymmetry between direct and indirect semiconductors should extend to other multijunction architectures pairing the two, including III-V-on-silicon tandems.
