  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 photo-induced 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 two increase in
photocurrent. This approach opens the door to probing and manipulating
photoelectrochemical processes in specific regions inside nominally opaque
media.
