Vertically stacked immobilized photocatalyst devices towards land-efficient solar hydrogen production.

Thin-film architectures offer a scalable strategy for photocatalytic hydrogen production but are often limited by weak interfacial adhesion, inefficient charge transport, and restricted land-use efficiency. Here, we report a swellable polymer matrix platform that immobilizes conjugated polymer photocatalysts and enables vertical integration into a three-dimensional stacking architecture. Immobilization within a flexible and transparent matrix enhances interfacial adhesion, charge transfer, and solvent accessibility without rigid substrates. The resulting films exhibit improved hydrogen evolution rates relative to thin-film configurations, supported by spectroscopic measurements that reveal efficient charge carrier generation and reduced recombination. The films also demonstrate sustained mechanical integrity and operational stability. Vertical stacking increases hydrogen production per unit area, and spectral splitting using complementary absorbers further improves performance relative to bulk-mixed systems. In this work, we show that polymer immobilization combined with vertical integration provides a practical route to improving land-use efficiency in solar hydrogen production.