Publication date: 15th December 2025
Perovskite materials offer exceptional advantages for next-generation multijunction photovoltaics due to their bandgap tunability, which enables the precise design of absorber layers across the solar spectrum. This tunability is particularly critical for all-perovskite triple-junction devices, which require bandgaps ranging from approximately 1.24 eV to 2.0 eV. While mid-bandgap perovskites are now well established, the extreme bandgaps necessary for triple-junction architectures remain insufficiently explored and present significant scientific and technological challenges.
For example, a major limitation arises from the poor compatibility of narrow-bandgap perovskites with emerging self-assembled monolayers (SAMs), which otherwise serve as highly effective hole-transporting layers (HTLs) in state-of-the-art perovskite solar cells. At the same time, the continued use of PEDOT:PSS as a hole-transporting material is no longer viable for advanced device architectures: its acidity affects the perovskite stability [1], and its strong parasitic absorption is detrimental to the current density of multijunction devices [2]. Overcoming these interface limitations is therefore essential for enabling efficient and stable triple-junction perovskite devices.
In this contribution, we highlight recent efforts to address these challenges through tailored interface engineering strategies and the development of alternative HTLs specifically designed for compatibility with extreme-bandgap perovskite absorbers. We present insights into key bottlenecks associated with narrow-bandgap materials, discuss methods to mitigate interfacial recombination and instability, and demonstrate how these approaches translate into improved device performance.
S. Mariotti acknowledges the Initiative and Networking Fund of the Helmholtz Association for the funding of the Helmholtz Investigator Group.
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