Self-Assembled Monolayers as Hole Transport Layers in Organic Solar Cells: Progress in Molecular Design and Device Engineering

• • Halogen-substituted SAMs in n-doped bulk-heterojunction OSCs yield 18.9% PCE (Adv Energy Mater, 2022), demonstrating that electron-withdrawing end-groups enhance hole extraction and reduce interfacial recombination—critical for scaling to >20% efficiency modules. • • Push–pull substituent SAMs break interfacial symmetry, enabling 19.67% PCE (Energy Environ Sci, 2025), a 0.77% absolute gain over conventional SAMs, directly translating to lower levelized cost of electricity (LCOE) for OSC deployment. • • Oligomeric carbazole phosphonic acid HTLs achieve 19.63% PCE (Adv Funct Mater, 2025), with phosphonic acid anchoring providing robust substrate binding and operational stability, essential for roll-to-roll manufacturing. • • Asymmetric SAMs enable binary PM6:Y6 OSCs with >19% efficiency (CCS Chem, 2025), reducing synthetic complexity and cost compared to symmetric counterparts, while maintaining high surface coverage and charge selectivity.