Inverted perovskite solar cells (PSCs) can be limited by non-radiative recombination at both the perovskite absorber surface and the perovskite/charge transport layer interface. Researchers from École Polytechnique Fédérale de Lausanne (EPFL), King Abdullah University of Science and Technology (KAUST), Centre d’Electronique et de Microtechnique (CSEM), Potsdam University and IPVF have introduced a bimolecular passivation strategy that simultaneously addresses these two bottlenecks by combining phosphonic acids with piperazinium chloride.
The phosphonic acids effectively passivate perovskite surface defects, such as lead-related traps, while piperazinium chloride improves the perovskite/electron transport layer interface by enhancing band alignment, introducing a favorable field effect, and homogenizing the surface potential. Together, these complementary effects increase the quasi-Fermi level splitting by approximately 100 mV, substantially improving voltage retention in devices.
The team's study yielded impressive results: two-terminal perovskite-on-silicon tandem solar cells achieved a certified open-circuit voltage of 2.0 V and efficiencies exceeding 31% for 1 cm² devices. Crucially, the strategy also scales well, with large-area modules of 60 cm² reaching a certified efficiency of 28.9% while maintaining uniform passivation quality. Inspired by approaches long used in crystalline silicon photovoltaics, such as AlOx/SiNx stacks in PERC and TOPCon architectures, this work illustrates the effectiveness of combining chemical and field-effect passivation.
Beyond efficiency, the study highlights the importance of molecular design for long-term stability. Although many passivation agents deliver short-term performance gains, they often destabilize the interfaces over time. The authors suggest that chemically resilient head groups, optimized counter-ions, and strong binding moieties to the electron transport layer will be key to building stable and durable inverted perovskite devices.
Overall, this work demonstrates how molecularly engineered passivation strategies not only push the efficiency of wide-bandgap perovskite solar cells but also pave the way for scalable, stable, and high-performance perovskite–silicon tandem photovoltaics.
