Publication date: 15th December 2025
Lab-scale devices have consistently showcased the efficiency potential of monolithic 2-terminal (2T) perovskite-silicon tandems, recently surpassing 34%. In addition, the technology has seen successful transfer from lab-scale devices to full-sized cells, with efficiencies of 28.6% on M10 and even commercially available modules reaching efficiencies up to 27%. However, if the perovskite-silicon tandem technology is to lead the efficiency increase of photovoltaic modules beyond 30%, the primary challenge to overcome is their long-term stability.
To test long-term operation performance and degradation including the underlying degradation mechanisms, we developed a bichromatic LED indoor stability testing setup with integrated, in-operando luminescence (PL/EL) imaging capabilities in addition to standard MPP tracking and in-situ I-V measurements. The periodic in-operando measurements provide us with a rich dataset enabling in-depth root cause analysis of degradation mechanisms of perovskite single junction and perovskite-silicon tandem solar cells either under indoor or outdoor operating conditions.
We utilized our monitoring setup to study the effect of individual layers within the single-junction perovskite stack on the long-term stability of the perovskite absorber with a FACs (Fa0.82Cs0.17Pb(I0.83Br0.17)3) composition, gradually building towards a full layer stack with additional AlOx capping as a moisture ingress barrier. We could distinguish three different PL intensity trends correlated with the stack composition, with perovskite absorber alone being the most stable in terms of PL intensity, ETL and HTL adding some dynamics to the initial PL stabilisation and the addition of copper layers leading to a tremendous PL intensity increase and device degradation after a few days. Nevertheless, across all tested samples, the presence of the ETL (C60) within the cell stack significantly promoted the formation of inhomogeneities across the device.
In addition to single junction perovskite devices, the monitoring setup was used for accelerated testing of perovskite-silicon tandem solar cells under cycled perovskite-/silicon-limited operating regimes, reaching t80 of more than 600 hours. Combining integral electrical parameters (MPP, I-V) and bias dependent luminescence images (PL at OC, SC, MPP) we are able to track the local evolution of the perovskite sub-cell degradation, as well as to extract the reversible and irreversible perovskite/tandem degradation rates within the different limitation regimes. Periodic PL images revealed that that the reversible degradation can be mainly attributed to lateral ion migration, whereas the irreversible degradation rate of the perovskite sub-cell is strongly correlated with the excess current density not extracted from the perovskite during silicon limitation.
We gratefully acknowledge support of the Slovenian Research and Innovation Agency under programme P2-0415 and project GC-0003 and support of the University of Ljubljana under project SN-ZRD/22-27/0510.
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