WAVELABS discussed how perovskite-silicon tandem solar cells require more complex characterization procedures than conventional silicon PV devices due to spectral sensitivity, hysteresis, and metastability
The company highlighted the importance of stabilized illumination, preconditioning, MPP tracking, and revised IEC testing procedures for improving tandem measurement consistency
Reliability testing, PL/EL imaging, and accelerated stability protocols are becoming increasingly important as tandem PV moves toward pilot-scale manufacturing and module-scale deployment
Perovskite-silicon tandem solar cells are introducing new challenges for photovoltaic characterization, requiring tighter spectral control, stabilization routines, and revised testing standards compared with conventional silicon PV devices. While silicon characterization has matured over decades with fast cycle times and low uncertainty levels, tandem devices introduce additional complexities associated with metastability, ion migration, and spectrum-dependent behavior.
At the recent TaiyangNews Conference on Next-Generation PV Technologies, Lukas Ziegler, Project Lead for Perovskite Tandem Technology at WAVELABS, discussed tandem photovoltaic device characterization from the perspective of a metrology-equipment provider. The presentation covered efficiency measurement, MPP tracking, hysteresis, scalability, and long-term reliability testing for perovskite tandem devices.
Ziegler explained that tandem PV technologies must ultimately compete against silicon not only in efficiency, but also in measurement accuracy, throughput, and reliability. Silicon module characterization currently achieves a measurement uncertainty as low as 0.9% at PTB in Germany, while production-line IV sweeps can be completed in roughly 30 ms with throughputs of 6,000 to 9,000 cells per hour. Silicon modules also exhibit annual degradation rates near 0.5% with efficiencies approaching 24%.
One of the main challenges in tandem characterization is spectral sensitivity. Unlike silicon solar cells, tandem devices are highly sensitive to changes in spectral distribution, requiring carefully adjusted illumination conditions during measurement. Existing IEC photovoltaic measurement standards, therefore, require that the illumination spectrum be adjusted based on external quantum efficiency (EQE) measurements of the tandem device. According to Ziegler, this makes conventional xenon flashers increasingly unsuitable for tandem characterization, driving the transition toward LED-based simulators with tighter spectral control and automated adjustment routines.
Stable illumination also becomes critical during maximum power point (MPP) tracking. Under continuous illumination, tandem devices can exhibit wake-up effects in which power output gradually increases during the first minutes of operation. Forward and reverse IV sweeps can also yield different results due to hysteresis effects. WAVELABS demonstrated LED-based solar simulators designed to maintain spectral deviation below 0.1% during long-duration MPP tracking.
According to Ziegler, tandem device measurements can also be strongly influenced by operating conditions such as temperature, light uniformity, electrical bias, and preconditioning routines. Different preconditioning states, including Voc, Isc, and MPP operation, can produce different characterization results. This necessitates dedicated stabilization and settling procedures before accurate measurements can be obtained.
Another major challenge comes from mobile ions within perovskite materials, which contribute to hysteresis and metastability. Scan-rate dependency in IV measurements can produce substantial variations in measured device performance, particularly at scan rates commonly used in silicon production lines. According to Ziegler, slow-moving cations within perovskite layers may require extended settling times before reaching steady-state operation. In tandem structures, these effects can combine with capacitance-driven hysteresis from silicon bottom-cell architectures such as TOPCon and HJT.
To improve consistency between laboratories and industrial testing environments, new testing procedures are currently being developed under the IEC TS 60904-1-4 draft standard for metastable photovoltaic devices. WAVELABS is also participating in this effort. The draft standard defines stabilization, preconditioning, and settling procedures intended to improve measurement reproducibility. The proposed workflow includes reverse and forward IV sweeps, settled MPP measurements, stabilized Voc and Isc measurements, followed by repeated IV characterization.
Beyond measurement accuracy, throughput remains another industrial challenge. Ziegler noted that tandem characterization cycle times remain significantly slower than those measured on silicon production lines. While the draft IEC procedure is intended to improve comparability between laboratories, inline tandem characterization still requires much faster equivalent measurement approaches. WAVELABS is currently developing tandem measurement routines to achieve cycle times below 500 ms.
Scaling tandem devices from laboratory cells to modules introduces additional challenges related to phase segregation, deposition non-uniformity, and thin-film uniformity. Filtered photoluminescence (PL) and electroluminescence (EL) imaging are increasingly being used to analyze large-area tandem devices and monitor thin-film quality. WAVELABS also demonstrated dual-camera systems with exchangeable filters capable of separately analyzing silicon and perovskite sub-cells within tandem structures.
Reliability testing formed another major part of the presentation. Industry groups are currently developing long-term consensus protocols for perovskite tandem stability testing using conditions such as 1-sun illumination, 85°C temperature exposure, and continuous MPP tracking. According to the data presented, increasing the testing temperature from 65°C to 85°C can accelerate degradation by approximately 3.5 times.
However, demonstrating a 30-year field lifetime could still require 10,000 to 20,000 hours of accelerated testing. This highlights the need for additional acceleration methods as tandem device stability continues to improve.
The final section of the presentation highlighted WAVELABS’ characterization platforms, ranging from small-area research tools to inline production systems and large-format module flashers. The company also discussed light soakers for stability testing, bifacial LED flashers for tandem modules, and inline steady-state measurement systems spanning applications from R&D cells to commercial modules. According to Ziegler, several recent tandem efficiency records, including devices from Oxford PV, LONGi, and Qcells, were characterized using WAVELABS testing systems.
The full presentation, titled Characterization of Tandem Photovoltaic Devices, is available on the TaiyangNews YouTube channel.