Daniele Padula

Delocalization versus Coherence under Vibrational and Environmental Disorder in Photoexcited Supramolecular Aggregates

IF 15.6 · 1 citations

Publisher Correction: Exciton transport in molecular organic semiconductors boosted by transient quantum delocalization

IF 15.7 · 1 citations

Identification of Unknown Inverted Singlet–Triplet Cores by High-Throughput Virtual Screening

IF 15.6 · 59 citations

Exciton transport in molecular organic semiconductors boosted by transient quantum delocalization

Abstract Designing molecular materials with very large exciton diffusion lengths would remove some of the intrinsic limitations of present-day organic optoelectronic devices. Yet, the nature of excitons in these materials is still not sufficiently well understood. Here we present Frenkel exciton surface hopping, an efficient method to propagate excitons through truly nano-scale materials by solving the time-dependent Schrödinger equation coupled to nuclear motion. We find a clear correlation between diffusion constant and quantum delocalization of the exciton. In materials featuring some of the highest diffusion lengths to date, e.g. the non-fullerene acceptor Y6, the exciton propagates via a transient delocalization mechanism, reminiscent to what was recently proposed for charge transport. Yet, the extent of delocalization is rather modest, even in Y6, and found to be limited by the relatively large exciton reorganization energy. On this basis we chart out a path for rationally improving exciton transport in organic optoelectronic materials.

IF 15.7 · 94 citations

Carrier Tunneling from Charge Transfer States in Organic Photovoltaic Cells

AbstractCharge transfer (CT) states play a key role in the functioning of organic solar cells; however, understanding the mechanism by which CT states dissociate efficiently into free charges remain a conceptual challenge. Here, the electric field dependent dynamics of charge generation in planar cyanine/fullerene photovoltaic cells is probed over a wide temperature range using time‐resolved Stark effect experiments, transient absorption, and photocurrent measurements. Results indicate that dissociation of thermalized CT states is the rate‐limiting step for all temperatures. The dissociation rate strongly depends on the field, but is temperature independent. The results also suggest that the yield of generated charges is temperature independent. Model electrostatic calculations illustrate that specific orientations of the cyanine crystal relative to C60 create a repulsive potential for an electron near the interface that is largely due to the quadrupole moment of the unit cell. In combination with the electron‐hole coulomb attraction and the electric field‐induced barrier lowering, a high‐energy potential barrier forms with a narrow width of a few nanometers. It is proposed that charge separation occurs via a field‐dependent electron tunneling mechanism through that barrier, which is temperature independent. The results support a thus far overlooked pathway for CT state dissociation via carrier tunneling.

IF 19.0 · 18 citations

Novel thermally activated delayed fluorescence materials by high-throughput virtual screening: going beyond donor–acceptor design

125 potential TADF candidates are identified through quantum chemistry calculations of 700 molecules derived from a database of 40 000 molecular semiconductors. Most of them are new and some do not belong to the class of donor–acceptor molecules.

IF 5.1 · 47 citations