Perovskite-silicon tandem solar cells have emerged as a global focal point in advanced photovoltaic research, offering the potential to exceed the Shockley–Queisser theoretical efficiency limit of single-junction silicon cells. Traditional silicon cells face inherent limitations due to thermal relaxation losses of high-energy photons. To overcome this, researchers are integrating wide-bandgap perovskites with silicon, enabling tandem architectures that reduce carrier thermalization losses and significantly improve solar energy utilization. These tandem devices are widely regarded as the next frontier in ultra-high-efficiency solar technology.
Despite rapid progress, performance of wide-bandgap perovskite sub-cells has been constrained by interfacial non-radiative recombination. This occurs primarily at the interface between the perovskite surface and the electron transport layer (ETL), as well as due to incomplete conformality and coverage of the hole transport layer (HTL) on textured silicon surfaces.
In September 2024, LONGi’s tandem research team published a landmark study in Nature, introducing a bilayer-intertwined passivation strategy. By integrating a nanoscale, discretely distributed lithium fluoride (LiF) ultrathin layer with an additional coating of diammonium diiodide molecules, the team achieved efficient electron extraction and significantly suppressed interfacial non-radiative recombination. This innovation enabled a certified power conversion efficiency of 33.9%—the first reported efficiency for a two-junction tandem solar cell to surpass the single-junction Shockley–Queisser limit of 33.7%. This marks a milestone in photovoltaic technology.
Building on this success, LONGi, in collaboration with Soochow University, addressed another key challenge: non-radiative recombination at the buried interface. Their research focused on novel organic self-assembled molecule (SAM) design. Unlike conventional symmetric carbazole-based SAMs, LONGi’s team developed an asymmetric carbazole-based SAM (HTL201), incorporating tailored spacer units and phosphonic acid anchoring groups flanking the carbazole core. This SAM serves as a hole-selective layer, improving carrier extraction and passivation in perovskite-silicon tandem cells.
This study was published in Nature on 7 July 2025 under the title “Efficient perovskite/silicon tandem with asymmetric self-assembly molecule.” It represents a significant advancement in interfacial engineering, paving the way for the next generation of ultra-efficient solar cells.
