Researchers from China's Southern University of Science and Technology, Xi’an Jiaotong University, City University of Hong Kong, Eastern Institute of Technology and Shenzhen Polytechnic University have developed a new molecular engineering strategy that overcomes a known bottleneck in perovskite solar cell (PSC) interfaces - self-aggregation of hole-selective self-assembled monolayers (SAMs) leading to poor interfacial contact and energy loss.
While perovskite solar technology made great strides in recent years, fine control of interfacial chemistry remains one of the key challenges limiting long-term stability and reproducibility. Conventional hole-transport SAMs often suffer from excessive intermolecular interactions, causing aggregation and misaligned energy levels that degrade charge extraction.
To tackle this issue, the team designed a bicarbazole-based dimeric molecule incorporating amide groups that act simultaneously as hydrogen-bond donors and acceptors. This configuration enables a three-dimensional hydrogen-bonding network - both among adjacent SAM molecules and between the SAM and the transparent conductive oxide substrate. The network guides a more ordered molecular packing, resulting in smoother, more homogeneous films and better energy-level alignment at the perovskite interface.
This molecular organization minimizes hole-transport losses and suppresses interfacial recombination, allowing the device to operate closer to its intrinsic photovoltaic potential.
Using this molecular layer, the researchers achieved a power conversion efficiency (PCE) of 21.56% for a 1.77 eV perovskite cell, with an open-circuit voltage (Voc) of 1.35 V and a fill factor (FF) of 85.76%. The same approach applied to a 1.56 eV single-junction PSC produced an impressive 26.80% PCE (certified 26.57% by J–V scan; 25.92% steady-state over 300 s).
The highlight of the study is the all-perovskite tandem device, integrating the optimized SAM design into both sub-cells. This tandem architecture delivered a record efficiency of 30.19% (certified 29.38% by J–V scan and 28.40% steady-state over 120 s) - among the highest reported for all-perovskite tandems to date.
At the atomic level, the dual amide units reinforce molecular alignment through directional hydrogen bonds, effectively “locking” the interface in place. This structure minimizes disorder-induced trap states and stabilizes the perovskite/SAM junction under light and thermal stress, addressing one of the main degradation pathways in PSCs.
This work demonstrates how rational supramolecular design - specifically, tuning hydrogen-bonding interactions - can simultaneously enhance charge transport and interfacial durability. The approach offers a generalizable route for improving the operational stability of next-generation perovskite solar cells.
