Amorphous silicon (a-Si:H) based solar cells are highly interesting in the context of hybrid (i.e. photovoltaic/ thermal) solar energy conversion. First, their large area capability and the variety of possible substrate materials permit to apply a-Si:H PV modules directly on the surface of conventional heat collectors at low cost. Further, the low temperature coefficient of a-Si:H cells (0.1%/K) allows operation of a-Si:H solar modules at temperatures as high as 100°C without substantial power loss. We focus on the thermal performance of such hybrid collectors based on a-Si:H cells, with emphasis on a ZnO coat on top of the solar cell. ZnO can be "tuned" to absorb the infrared part of the sunlight and, at the same time, its emission coefficient for heat-radiation is nearly as low as that of optimized selective surfaces used in thermal collectors. We propose a collector structure with a high potential for the thermal conversion efficiency while maintaining a high electrical conversion efficiency.