Coherent Control of Photocurrent in a Strongly Scattering Photoelectrochemical System

A fundamental issue that limits the efficiency of many photoelectrochemical systems is that the photon absorption length is typically much longer than the electron diffusion length. Various photon management schemes have been developed to enhance light absorption; one simple approach is to use randomly scattering media to enable broadband and wide-angle enhancement. However, such systems are often opaque, making it difficult to probe photoinduced processes. Here we use wave interference effects to modify the spatial distribution of light inside a highly scattering dye-sensitized solar cell to control photon absorption in a space-dependent manner. By shaping the incident wavefront of a laser beam, we enhance or suppress photocurrent by increasing or decreasing light concentration on the front side of the mesoporous photoanode where the collection efficiency of photoelectrons is maximal. Enhanced light absorption is achieved by reducing reflection through the open boundary of the photoanode via destructive interference, leading to a factor of 2 increase in photocurrent. This approach opens the door to probing and manipulating photoelectrochemical processes in specific regions inside nominally opaque media.