An international research collaboration involving City University of Hong Kong, Ludwig-Maximilians-Universität München (LMU), Southern University of Science and Technology (SUSTech), King Abdullah University of Science and Technology (KAUST), Marmara University, Kaneka Corporation, and Shenzhen MOLEC New Energy Technology has reported an advance in perovskite - silicon tandem photovoltaics, achieving a certified power conversion efficiency (PCE) of 31.4% on industry-compatible Czochralski (CZ) silicon substrates.
The recent work focuses on the molecular engineering of self-assembled monolayers (SAMs) that mediate charge recombination at the perovskite/silicon interface. Conventional alkyl-chain-based SAMs often exhibit aggregation on textured silicon, leading to inefficient charge transport. To overcome this limitation, the team synthesized a conjugated linker SAM, (4-(7H-dibenzo[c,g]carbazol-7-yl)phenyl)phosphonic acid (Bz-PhpPACz), designed to enable efficient hole extraction and uniform coverage on pyramidally textured surfaces.
A pivotal discovery arose during the investigation of commercial SAM precursors: trace bromine impurities present in certain 4PADCB derivatives were found to beneficially modulate interface properties. While initially unintended, these bromine species were shown to enhance energy-level alignment, passivate defect states, and relieve strain within the perovskite layer. Guided by this insight, the team purposefully synthesized a bromine-functionalized analogue, (Bz-PhpPABrCz), and developed a binary SAM system combining brominated and non-brominated species in optimized ratios.
Comprehensive structural, electronic, and photovoltaic characterizations revealed that the conjugated, bromine-engineered SAMs promote denser molecular packing, improved interfacial energy alignment, and enhanced film crystallinity. The resulting mixed SAMs yielded notable improvements in fill factor and open-circuit voltage compared with conventional architectures. Importantly, these optimized interfaces exhibited superior stability and reproducibility under prolonged operational conditions, underlining the potential of chemically tailored interlayers for scalable tandem photovoltaics.
This molecular-design framework emphasizes that even subtle variations in chemical composition can profoundly influence interfacial energetics and device performance. The findings establish molecular-level precision and impurity control as critical levers for advancing high-efficiency, durable perovskite–silicon tandem solar cells, with implications extending to other emerging optoelectronic systems.
