Molecular orientation-dependent energetic shifts in solution-processed non-fullerene acceptors and their impact on organic photovoltaic performance

The non-fullerene acceptors (NFAs) employed in state-of-art organic photovoltaics (OPVs) often exhibit strong quadrupole moments which can strongly impact on material energetics. Herein, we show that changing the orientation of Y6, a prototypical NFA, from face-on to more edge-on by using different processing solvents causes a significant energetic shift of up to 210 meV. The impact of this energetic shift on OPV performance is investigated in both bilayer and bulk-heterojunction (BHJ) devices with PM6 polymer donor. The device electronic bandgap and the rate of non-geminate recombination are found to depend on the Y6 orientation in both bilayer and BHJ devices, attributed to the quadrupole moment-induced band bending. Analogous energetic shifts are also observed in other common polymer/NFA blends, which correlates well with NFA quadrupole moments. This work demonstrates the key impact of NFA quadruple moments and molecular orientation on material energetics and thereby on the efficiency of high-performance OPVs

Asymmetric charge carrier transfer and transport in planar lead halide perovskite solar cells

Understanding charge carrier extraction from the perovskite photoactive layer is critical to optimizing the design of perovskite solar cells. Herein, we demonstrate a simple time-resolved photoluminescence method to characterize the kinetics of charge transport across the bulk perovskite and charge transfer from the perovskite layer to the interlayers, elucidating the dependence of these dynamics on film thickness, grain boundaries (GBs), and interlayers. Using asymmetric laser excitation, we selectively probe charge transport by generating charges both close to and far from the heterojunction interface and correlate these results with device performance. We observe that both film thickness and GBs affect the asymmetry between electron and hole charge transport across the bulk perovskite and charge transfer from the bulk perovskite to the respective interlayers

Influence of provenance transfer on the growth and survival of Picea abies provenances

Two provenance experiments with Norway spruce in Slovakia were used to reveal trends in the behaviour of provenances after their transfer. Regressions between the average height and survival of provenances and the differences between the geographic and selected climatic characteristics of the place of origin and provenance plots were significant for most of the characteristics tested. Data from the experiment with Polish and Slovak provenances from 1972 indicated that transfer into warmer regions with a longer vegetation period results in improved height growth and survival, with the exception of survival at initial stages. The experiment from 1964 with a broader altitudinal range of provenance plots, but with unadjusted latest measurements at individual plots available, revealed the best height growth of Slovak Norway spruce provenances after their transfer to sites with the mean annual temperature approximately 1°C higher and with the vegetation period 12 days longer than at places of origin. Transfer into lower altitudes, a warmer climate and a longer vegetation period improved survival. In both experiments, transfer to areas with increased rainfall had a negative effect on growth, which is probably associated with the fact that provenances are not able to exploit additional precipitation for the growth in areas with a colder climate and a shorter vegetation period

Molecular orientation-dependent energetic shifts in solution-processed non-fullerene acceptors and their impact on organic photovoltaic performance

Non-fullerene acceptors with large quadrupole moments strongly affect thin-film energetics. Here, the authors show a significant energetic shift (>200 meV) of Y6 upon changing its orientation from face-on to more edge-on using different solvents and its critical impact on organic photovoltaics