Boron‐Doped Diamond as an Efficient Back Contact to Thermally Grown TiO 2 Photoelectrodes

In the present work, we investigate the efficiency of TiO 2 photoelectrode layers on boron‐doped diamond foil (BDDF) in comparison with a classic conducting glass (fluorine‐doped tin oxide, FTO) back contact. Crystalline thin TiO 2 layers were prepared on the substrates by two different methods: (i) deposition of metallic Ti thin films followed by thermal oxidation to form TiO 2 (TO‐TiO 2 ), (ii) reactive sputter deposition of TiO 2 thin films and crystallization of these layers (SP‐TiO 2 ). The optimized layers show that TO‐TiO 2 films on BDDF deliver a significantly higher incident photon to current efficiency (IPCE) compared to directly sputtered SP‐TiO 2 layers and these layers on BDDF also outperform FTO as a back contact. We ascribe this beneficial effect of the BDDF back contact to the formation of an intermediate conductive phase of Ti carbides at the TO‐TiO 2 /BDDF interface.