Conversion Efficiency Profile Research Articles

Enhancement of performance in chlorophyll-based bulk-heterojunction organic-inorganic solar cells upon aggregate management via solvent engineering

Abstract Chlorophylls are the most abundant bipolar organic semiconductor found in nature. We demonstrated novel bulk-heterojunction organic-inorganic solar cells (OISCs) in which a carboxylated chlorophyll derivative (H2Chl-1) sensitizing mesoporous TiO2 functioned as an n-type electron acceptor and self-aggregates of zinc chlorophyll (ZnChl-2) functioned as a p-type electron donor. In this work, we employed chloroform (CF), chlorobenzene (CB), and their mixtures as processing solvents to manage the morphology of ZnChl-2 aggregates and the pore-filling of ZnChl-2 into mesoporous TiO2. ZnChl-2 aggregates generated from a mixed solvents (CF:CB = 2:1) exhibited the smallest surface roughness and most efficient charge separation and the power conversion efficiency of OISCs was substantially improved to 2.13%. Importantly, the incident photon-to-current conversion efficiency profiles of these OISCs consisted of the spectral components of both TiO2-attached H2Chl-1 and self-aggregated ZnChl-2, indicating that efficient charge separation can occur at the interface between these two chlorophyll species.

Functionalization of a ruthenium-diacetylide organometallic complex as a next-generation push-pull chromophore.

The design and preparation of an asymmetric ruthenium-diacetylide organometallic complex was successfully achieved to provide an original donor-π-[M]-π-acceptor architecture, in which [M] corresponds to the [Ru(dppe)2] (dppe: bisdiphenylphosphinoethane) metal fragment. The charge-transfer processes occurring upon photoexcitation of the push-pull metal-dialkynyl σ complex were investigated by combining experimental and theoretical data. The novel push-pull complex, appropriately end capped with an anchoring carboxylic acid function, was further adsorbed onto a semiconducting metal oxide porous thin film to serve as a photosensitizer in hybrid solar cells. The resulting photoactive material, when embedded in dye-sensitized solar cell devices, showed a good spectral response with a broad incident photon-to-current conversion efficiency profile and a power conversion efficiency that reached 7.3 %. Thus, this material paves the way to a new generation of organometallic chromophores for photovoltaic applications.