Perovskite silicon tandem solar cells have become a central focus in advanced photovoltaic research worldwide, with the potential to surpass the Shockley Queisser theoretical efficiency limit of single junction silicon cells. Traditional silicon cells are limited by thermal relaxation losses from high energy photons. To address this issue, researchers are combining wide-bandgap perovskites with silicon, creating tandem architectures that minimize carrier thermalization losses and greatly enhance solar energy utilization. These tandem devices are widely viewed as the next frontier in ultra high efficiency solar technology.
Despite significant advancements, the performance of wide-bandgap perovskite sub-cells has been limited by interfacial non-radiative recombination. This phenomenon primarily occurs 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 groundbreaking 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 reduced interfacial non-radiative recombination. This innovation led to a certified power conversion efficiency of 33.9% the first reported efficiency for a two-junction tandem solar cell to exceed the single-junction Shockley–Queisser limit of 33.7%. This achievement marks a milestone in photovoltaic technology.
Building on this success, LONGi, in partnership with Soochow University, tackled another critical challenge: non-radiative recombination at the buried interface. Their research concentrated on a novel organic self-assembled molecule (SAM) design. In contrast to traditional symmetric carbazole-based SAMs, LONGi’s team developed an asymmetric carbazole-based SAM (HTL201), which incorporates tailored spacer units and phosphonic acid anchoring groups flanking the carbazole core. This SAM functions as a hole-selective layer, enhancing carrier extraction and passivation in perovskite-silicon tandem cells.
Source: LONGi
