Excitation Energy Dependent Charge Separation at Hole-Transporting Dye/TiO₂ Hetero Interface

Abstract

Interfacial charge separation in hybrid solar cells depends on both the energetic alignment and electronic coupling between the inorganic and organic semiconducting materials at the hetero interface. In the present work, bilayer solar cells comprising the small molecular semiconducting dye TDCV-TPA (tris-(thienylene-vinylene)-triphenylamine) and dense titanium dioxide (TiO 2 ) films were investigated. The internal quantum efficiency and degree of photoluminescence quenching were found to be excitation energy dependent. The molecular interaction and interfacial energy level alignment was investigated using a combination of UV−vis and photoelectron spectroscopy (PES). Stationary and time-dependent density functional theory calculations were used to assign and distinguish between different experimentally determined molecular energy levels (PES) and electronic transitions (UV−vis). Photoelectron spectroscopy results suggest surface induced interactions of TDCV-TPA with TiO 2 involving the peripheral CN-groups of the molecule which would imply a favorable electronic coupling for photoinduced interfacial charge transfer. In an energy level diagram distinguishing between the different electronic transitions in the molecule, the differences in the thermodynamic driving force for electron injection from the excited states were found small. Therefore, it is suggested that the observed higher internal quantum efficiency at shorter wavelength can be rationalized by a more favorable driving force for the regeneration of holes created at the hetero interface at higher excitation energy.

Opticalin situmonitoring during the synthesis of halide perovskite solar cells reveals formation kinetics and evolution of optoelectronic properties

“…The chloride-content in annealed lms was found to be only a few percent, varying throughout the depth of the lm. 30,[35][36][37][38] The formation process itself and especially the crystalline intermediate phases containing chloride were found to be of signicant importance, as they template the growth of large grainsize, oriented and high-quality material. Several studies have been carried out to elucidate the key intermediates and lm formation kinetics.…”

Molecular Electronic Effects on the Thermal Grafting of Aryl Iodides to TiO2 Surfaces

“…The functionalization of metal oxides using conjugated molecules is of interest for emerging solar energy harvesting applications. − For these new applications, functionalizing metal oxides with photodyes − and photocatalysts ,− integrates the mechanical and electrical properties of the oxide with the electronic tunability of the arene. This sensitization forms a new molecule–metal oxide interface in these devices that affects overall device properties.…”

“…This sensitization forms a new molecule–metal oxide interface in these devices that affects overall device properties. As a consequence, there has been sustained interest in studying and manipulating the molecule–metal oxide interface. − ,− …”