Macroporous Interlayers Stabilize Long-Lived Hole Polarons in Organic Semiconductor Photoanodes

Integrating alternative oxidation reactions (AORs) into photoelectrochemical (PEC) systems is promising for unassisted hydrogen production and value-added chemical synthesis, yet organic semiconductor (OS) photoanodes suffer from poor charge extraction and short carrier lifetimes. Here, we address this bottleneck by stabilizing long-lived hole polarons through macroporous tin oxide (mcSnO2) interlayers. Transient absorption spectroscopy reveals that accelerated electron extraction through mcSnO2 stabilizes hole polaron states, substantially prolonging carrier lifetimes. Consequently, the optimized organic photoanodes outperform bare counterparts by more than 5.5-fold, retaining 74% of their initial photocurrent over 15 h for iodide oxidation and 61% over 35 h for ascorbic acid oxidation. Furthermore, integrating this robust organic photoanode with an OS-based photocathode enables the first bias-free organic PEC tandem cell coupling hydrogen evolution with AORs, delivering a remarkable solar-to-hydrogen conversion efficiency of 1.4%. These findings establish interfacial carrier lifetime engineering as an effective strategy for realizing high-performance and durable organic PEC systems.