Computational study of film morphology impact on light absorption in particulate Ta3N5/Si photoanodes for water splitting

A large class of photoelectrodes for water splitting are processed by assembling nanoparticles onto a silicon solar cell substrate. A fundamental question is the optimal size of constituent nanoparticles that maximizes optical absorption in the photoanode. We use electromagnetic optical calculations to study the impact of particle size on optical absorption of Ta3N5/Si tandem photoanodes. We found that optical absorption efficiency dramatically increases when particle support Mie resonances, independent of particle shape. Subsequently, monolayers of resonant-size particulate and thin films of Ta3N5 on silicon substrate are studied. Ta3N5 limits overall performance of Ta3N5/Si tandem device in both devices with the particulate one showing better performance. We take into account material charge transport properties and conditions of imperfect surface coverage of Si solar cell with Ta3N5 nanoparticle. Furthermore, we found that an intermediate reflective layer placed between Ta3N5 and Si solar cell improves photocurrent density of Ta3N5 and the tandem device.