Constructing Ordered Sensitized Heterojunctions: Bottom-Up Electrochemical Synthesis of p-Type Semiconductors in Oriented n-TiO2 Nanotube Arrays

Fabrication of efficient semiconductor-sensitized bulk heterojunction solar cells requires the complete filling of the pore system of one semiconductor (host) material with nanoscale dimensions (<100 nm) with a different semiconductor (guest) material. Because of the small pore size and electrical conductivity of the host material, it is challenging to employ electrochemical approaches to fill the entire pore network. Typically, during the electrochemical deposition process, the guest material blocks the pores of the host, precluding complete pore filling. We describe a general synthetic strategy for spatially controlling the growth of p-type semiconductors in the nanopores of electrically conducting n-type materials. As an illustration of this strategy, we report on the facile electrochemical deposition of p-CulnSe(2) in nanoporous anatase n-TiO2 oriented nanotube arrays and nanoparticle films. We show that by controlling the ambipolar diffusion length the p-type semiconductors can be deposited from the bottom-up, resulting in complete pore filling.