Engineering Hydrogen-Bond Networks in Self-Assembled Molecules Boosts All-Perovskite Tandem Solar Cell Efficiency
All-perovskite tandem solar cells (TSCs) are poised to surpass the Shockley–Queisser limit of single-junction perovskite solar cells (PSCs) by integrating wide- and narrow-bandgap subcells to broaden spectral utilization. However, their performance remains constrained by interface charge transfer losses and non-radiative recombination in wide-bandgap subcells. Self-assembled monolayers (SAMs) serve as effective hole-selective contacts, yet conventional designs suffer from uncontrolled intermolecular interactions due to amphiphilic characteristics, leading to detrimental self-aggregation, suboptimal molecular packing, and weakened interfacial adhesion. In a recent breakthrough published in Nature Energy, Wang et al. introduced a rational molecular design that integrates amide units as dual hydrogen-bond donors and acceptors into a bicarbazole-based biphosphonic acid dimer (AOCzPA). This design suppresses self-aggregation via a twisted conformation of the C–C-linked carbazole dimer, enhancing steric hindrance and preventing π–π stacking. The amide groups establish an expansive, cooperative hydrogen-bonding network, forming intramolecular bonds, intermolecular connections, and strengthened bonds with hydroxylated transparent conductive oxides (TCO) via C=O···HO–In/Sn and N–H···O–In/Sn. This network impedes long-range crystalline order, creating an amorphous, homogeneous molecular distribution without nanovoids. Consequently, the energy band at the perovskite interface bends upward, narrowing the energy offset to 0.42 eV and aligning HOMO levels for barrier-free hole extraction. The strategy yields exceptional performance: 1.77 eV single-junction wide-bandgap PSCs achieve a PCE of 21.56%, V_OC of 1.35 V, and FF of 85.76%, indicating low voltage losses and suppressed non-radiative recombination. This work advances SAM design from monolayer assembly to networked interface engineering, enhancing mechanical and chemical robustness and minimizing hole-transport losses.