Organic photovoltaics based on non-fullerene acceptors (NFAs) show record efficiency of 16 to 17% and increased photovoltage owing to the low driving force for interfacial chargetransfer. However, the low driving force potentially slows down charge generation, leading to a tradeoff between voltage and current. Here, we disentangle the intrinsic charge-transfer rates from morphology-dependent exciton diffusion for a series of polymer:NFA systems. Moreover, we establish the influence of the interfacial energetics on the electron and hole transfer rates separately. We demonstrate that charge-transfer timescales remain at a few hundred femtoseconds even at near-zero driving force, which is consistent with the rates predicted by Marcus theory in the normal region, at moderate electronic coupling and at low re-organization energy. Thus, in the design of highly efficient devices, the energy offset at the donor:acceptor interface can be minimized without jeopardizing the charge-transfer rate and without concerns about a current-voltage tradeoff.

The electrochemical dedoping and redoping processes of a thin poly(3,4ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) film immersed in an electrolyte are studied at different temperatures with time-resolved spectro electrochemistry in the visible and near-infrared range. The spectral signatures of neutral, polaronic, and bipolaronic states of PEDOT are resolved using multivariate curve resolution analysis. Kinetic modeling of their dynamics reveals that both the dedoping and redoping are sequential processes and occur within a few hundred milliseconds in the system. Evaluation of the temperature-dependence with the Van't Hoff, Arrhenius, and Eyring formalisms highlights the role of entropy in both the establishment of the redox equilibrium at a given voltage bias and the reaction rates. This study provides a significant understanding of the fundamental mechanisms determining the level and rate of the electrochemical processes in PEDOT:PSS and will help tailor the design of faster and more efficient bioelectronic devices based on mixed ionic-electronic conductors.

We introduce a passive common-path interferometer to replace Michelson interferometers in Fourier transform spectroscopy. Our device exploits birefringence to introduce a highly accurate delay between two orthogonal polarization components by continuously varying the material thickness. Thanks to its inherent delay stability and reproducibility, it can be used even for short wavelengths (down to ~200nm) without the need for any active control or position tracking. We first demonstrate its performances in linear spectroscopy, by implementing a spectrometer and a spectrophotometer. We then extend its use to nonlinear spectroscopy and, in combination with lock-in detection at MHz modulation frequencies, illustrate its application to pump-probe spectroscopy with high sensitivity (ΔT⁄T<3·10-6 in 1-s integration time) and broad spectral coverage (>500nm) and to broadband stimulated Raman scattering microscopy in the CH stretching\ud region

We introduce a novel configuration for the broadband measurement of the optical activity of molecules, combining time-domain detection with heterodyne amplification. A birefringent common-path polarization-division interferometer creates two phase-locked replicas of the input light with orthogonal polarization. The more intense replica interacts with the sample, producing a chiral free-induction decay field, which interferes with the other replica, acting as a time-delayed phase-coherent local oscillator. By recording the delay-dependent interferogram, we obtain by a Fourier transform both the circular dichroism and circular birefringence spectra. Our compact, low-cost setup accepts ultrashort light pulses, making it suitable for measurement of transient optical activity.