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Beyond their applications in organic light-emitting diodes (OLEDs), thermally activated delayed fluorescence (TADF) materials can also make good photonic markers. Time-gated measurement of their delayed emission enables "background-free" imaging in, for example, biological systems, because no naturally-occurring compounds exhibit such long-lived emission. Attaching a strongly-absorbing antenna, such as a phenylene ethynylene oligomer, to the TADF core would be of interest to increase their brightness as photonic markers. With this motivation, we study a sequence of TADF-oligomer conjugates with oligomers of varying length and show that, even when the absorption of the oligomer is almost resonant with the charge-transfer absorption of the TADF core, the antenna transfers energy to the TADF core. We study this series of compounds with time resolved emission and transient absorption spectroscopy and find that the delayed fluorescence is essentially turned-off for the longer antennae. Interestingly, we find that the turn-off of the delayed fluorescence is not caused by quenching of the TADF charge-transfer triplet state due to triplet energy transfer of the lower-lying triplet state to the antenna, but must be associated with a decrease in the reverse intersystem crossing rate. These results are of relevance for the further development of TADF "dyes" and also, in the broader context, for understanding the dynamics of TADF molecules in the vicinity of energy donors/acceptors (i.e., in fluorescent OLEDs wherein TADF molecules are used as an assistant dopant).

Petal textures exhibit outstanding broadband and omnidirectional light harvesting properties on solar cells [1,2] + by choice of low surface energy materials their self-cleaning properties can be harnessed [3]. A hot embossing routine via robust nickel embossing tools has been developed for a large area fabrication of such textures.

Most high-efficiency perovskite solar cells (PSCs) rely on titanium dioxide (TiO 2 ) electron transport layers (ETLs) that are usually processed at high temperature (>450 °C). Consequently, a fully solution-based process of PSCs with TiO 2 ETL on inexpensive flexible polymer substrates is not feasible. Therefore, a scalable low-temperature TiO 2 ETL is developed based on presynthesized crystalline nanoparticle TiO 2 (np-TiO 2 ). The presented synthesis process offers control over the doping, the hydrodynamic diameter, and the solvent of the np-TiO 2 . High initial power conversion efficiency (PCE) of 19.5% (stabilized at 18.2%) of PSC processed on the np-TiO 2 ETL is demonstrated with spin-coated methylammonium lead iodide (CH 3 NH 3 PbI 3 ). Furthermore, it is shown that other perovskite absorber layers that include evaporated CH 3 NH 3 PbI 3 and triple cation perovskite, Cs 0.1 (MA 0.17 FA 0.83 ) 0.9 Pb(I 0.83 Br 0.17 ) 3 , also show very high initial PCE, 14.5% and 19%, respectively. The possibility of doping the np-TiO 2 with niobium (Nb 5+ ) also reduces the resistance of the np-TiO 2 ETL, allowing for thick ETLs that are beneficial for rough substrates. Facile upscaling of the deposition of the np-TiO 2 ETL by inkjet printing, blade coating, and slot-die coating is also demonstrated, having high uniformity, resulting in prototype PSCs with a stable PCE > 15%.

We introduce shape-memory polymers (SMP) as substrate material for active optical devices. As an exemplary application we build a tunable organic semiconductor distributed feedback (DFB) laser. Hence, we transfer a second order Bragg grating with a period of 400 nm into SMP foils by hot embossing. The composite organic gain medium Alq3:DCM evaporated on the SMP substrate serves as laser active material. Mechanical stretching of the substrate increases the grating period temporarily and triggering the shape-memory effect afterwards reduces the period on demand. In this way, we can adjust the grating period to achieve a broad continuously tuning of the laser emission wavelength by 30 nm.

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In this letter, we discuss how the nonmodal emission regime's far field of a broad-area vertical-cavity surface-emitting laser (BA-VCSEL) can be used for low-speckle laser projection. A microlens beam homogenizer is used to exploit the low spatial coherence of the VCSEL's far field in the nonmodal emission regime. Using far-field instead of near-field illumination of the homogenizer has some important advantages for a practical projection system: the field emitted by the VCSEL can be directly projected onto the homogenizer without the need for additional lenses or accurate alignment. Speckle contrast values as low as 2.5% are measured and in good agreement with modeled contrast values.