5 research outputs found
Multiple exciton generation in quantum dot-based solar cells
Multiple exciton generation (MEG) in quantum-confined semiconductors is the process by which multiple bound charge-carrier pairs are generated after absorption of a single high-energy photon. Such charge-carrier multiplication effects have been highlighted as particularly beneficial for solar cells where they have the potential to increase the photocurrent significantly. Indeed, recent research efforts have proved that more than one charge-carrier pair per incident solar photon can be extracted in photovoltaic devices incorporating quantum-confined semiconductors. While these proof-of-concept applications underline the potential of MEG in solar cells, the impact of the carrier multiplication effect on the device performance remains rather low. This review covers recent advancements in the understanding and application of MEG as a photocurrent-enhancing mechanism in quantum dot-based photovoltaics
Star-shaped fluorene–BODIPY oligomers: versatile donor–acceptor systems for luminescent solar concentrators
Luminescent solar concentrators (LSCs) are waveguides doped with luminescent centers that can spectrally and spatially concentrate sunlight. They can reduce the cost of photovoltaic energy production and are attractive prospects for photobioreactors and building-integrated applications. Reabsorption, caused by non-zero overlap between the absorption and emission spectra of the light-emitting centers, often limits LSC efficiency. Donor–acceptor energy-transfer complexes are one method to mitigate reabsorption by shifting the emission away from the main absorption peak. Here we introduce versatile star-shaped donor–acceptor molecules based on a central BODIPY energy acceptor with oligofluorene donor side units. Varying the oligofluorene chain length alters the relative oscillator strengths of the donor and acceptor, changing the severity of reabsorption for a given donor density, but also changing the luminescence yield and emission spectrum. We performed comprehensive device measurements and Monte Carlo ray tracing simulations of LSCs containing three oligofluorene–BODIPY donor–acceptor systems with different oligofluorene chain lengths, and then extended the simulation to study hypothetical analogs with higher donor–acceptor ratios and different terminal acceptors. We found that the measured structures permit waveguide propagation lengths on a par with state-of-the-art nanocrystalline emitters, while the proposed structures are viable candidates for photobioreactor and energy production roles and should be synthesized
Size and Energy Level Tuning of Quantum Dot Solids via a Hybrid Ligand Complex
The performance of quantum dots (QDs)
in optoelectronic devices
suffers as a result of sub-bandgap states induced by the large fraction
of atoms on the surface of QDs. Recent progress in passivating these
surface states with thiol ligands and halide ions has led to competitive
efficiencies. Here, we apply a hybrid ligand mixture to passivate
PbSe QD sub-bandgap tail states via a low-temperature, solid-state
ligand exchange. We show that this ligand mixture allows tuning of
the energy levels and the physical QD size in the solid state during
film formation. We hereby present a novel, postsynthetic path to tune
the properties of QD films