Artificial photosynthesis by photoelectrocatalysis is one of the most promising ways to store solar energy in the form of fuels, thus constituting a sustainable alternative to fossil fuels.[1,2] Conjugated polymers (CPs) are used as part of some photoelectrodes due to their good conductivity and the possibility to tailor their optoelectronic properties at the molecular level. Some of the most used CPs, such as PEDOT, have a linear structure; which makes them easy to process as thin films, but also unstable under UV illumination if they are in contact with water.[3] Conjugated Porous Polymers (CPP)[3–5] show higher stability due to their 3D structure. However, it is difficult to produce thin films with them by conventional methods such as drop casting or spin coating because of their morphology.
Thanks to the electropolymerization process, we are able to prepare homogeneous, transparent and light-absorbing CPP films both on conducting glass substrates and on inorganic semiconductors. One of these CPPs, IEP-19 (Imdea Energy Polymer-19), has been synthesized for the first time and it shows promising photocurrents, which are significantly higher than those of a previously known CPP with a similar structure: CPP-3TB. Moreover, hybrid photoanodes where the CPP is electropolymerized on top of the inorganic semiconductor present higher photocurrents than the semiconductors alone, showing a synergistic effect between the organic and inorganic semiconductors. These results will be explained according to the optical, photoelectrochemical and morphological properties of the photoanodes.

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