Imaging-based beam steering for free-space optical communication.

Imaging-based beam steering (IBBS) provides a route to compact, low-power, and low-cost beam steering ideal for mobile free-space optical communications (FSOC), LIDAR imaging, and other active illumination applications. In IBBS, a lens passively maps each pixel of a 2D emitter array into a unique line-of-sight direction. Electronic beam steering of multiple beams with dynamic beam shaping is implemented via pixel selection. We demonstrate efficient collection and collimation of light from an organic LED array into 1.24 mrad divergence beams with pointing accuracy of 5.5 mrad and demonstrate a 41 m optical link. Simulations and scaling analysis of IBBS-FSOC links predict effective ranges >1 km using high-brightness vertical-cavity surface-emitting laser arrays.

Independent control of bulk and interfacial morphologies of small molecular weight organic heterojunction solar cells.

We demonstrate that solvent vapor annealing of small molecular weight organic heterojunctions can be used to independently control the interface and bulk thin-film morphologies, thereby modifying charge transport and exciton dissociation in these structures. As an example, we anneal diphenyl-functionalized squaraine (DPSQ)/C(60) heterojunctions before or after the deposition of C(60). Solvent vapor annealing of DPSQ before C(60) deposition results in molecular order at the heterointerface. Organic photovoltaics based on this process have reduced open circuit voltages and power conversion efficiencies relative to as-cast devices. In contrast, annealing following C(60) deposition locks in interface disorder found in unannealed junctions while improving order in the thin-film bulk. This results in an increase in short circuit current by >30% while maintaining the open circuit voltage of the as-cast heterojunction device. These results are analyzed in terms of recombination dynamics at excitonic heterojunctions and demonstrate that the optimal organic photovoltaic morphology is characterized by interfacial disorder to minimize polaron-pair recombination, while improved crystallinity in the bulk increases exciton and charge transport efficiency in the active region.