The impact of side chain elongation from the Y6 to Y6-12 acceptor in organic solar cells: a fundamental study from molecules to devices

Abstract

The introduction of non-fullerene acceptors in organic solar cells has reboosted the field of organic photovoltaics by reaching unprecedented values of conversion efficiency (up to 18% after deep optimization) that...

Improving Performance of Organic Photovoltaic Devices under Low Illuminations

“…The PCE values of the devices processed with CB and CF are 14.5% and 14.3%, respectively. This confirms that the increase in the size of the acceptor side chains enables the possibility of using high boiling point solvents to process the active layer with a desired morphology, similar to what has been reported in the literature. , …”

“…It should be stressed that for typical OPV devices, particularly those based on Y6 acceptors, low boiling point solvents, mainly CF with a boiling point of 61 °C, are used to achieve the desired donor–acceptor phase separation in the active layer and to improve the quantum efficiency of the devices. , Replacing the low boiling point solvent with a high boiling point solvent with a slower evaporation rate often leads to an increase in phase separation in the active layer. This gives rise to a reduced quantum efficiency and poor performance of OPV device. ,− For instance, for the blend of PM6:Y6, using CF as the processing solvent allowed us to realize a PCE of 14.8%, with J SC about 25.1 mA cm –2 , for the OPV device under the AM1.5 illumination (Figure S7), while the PCE in the OPV device is only 11.8%, with a J SC of 21.0 mA cm –2 , using the high boiling point solvent chlorobenzene (CB) with a boiling point of 132 °C to process the active layer (Figure S7). Similar results have also been reported elsewhere. ,,,, Although the typical organic active layers are processed using a low boiling point solvent, one exception was found for the active layer based on acceptors with enlarged side chains: Increasing the size of the side chains on the inner core of Y6 molecules enabled the possibility of using high boiling point solvents for processing the active layer with desired morphologies and high photovoltaic performance. , Therefore, we selected Y6OD, which compared to Y6 has significantly large side chains, and employed the high boiling point CB to construct OPV devices for the investigation regarding the role the processing solvent plays in determining the density of traps and the performance of OPV devices under low illumination intensities.…”

“…47,53,54,56,57 Although the typical organic active layers are processed using a low boiling point solvent, one exception was found for the active layer based on acceptors with enlarged side chains: Increasing the size of the side chains on the inner core of Y6 molecules enabled the possibility of using high boiling point solvents for processing the active layer with desired morphologies and high photovoltaic performance. 54,55 Therefore, we selected Y6OD, which compared to Y6 has significantly large side chains, and employed the high boiling point CB to construct OPV devices for the investigation regarding the role the processing solvent plays in determining the density of traps and the performance of OPV devices under low illumination intensities. First, we investigated the impact of the change of the solvent on the morphology of the active layer based on PM6:Y6OD, using atomic force microscopy (AFM).…”

“…This confirms that the increase in the size of the acceptor side chains enables the possibility of using high boiling point solvents to process the active layer with a desired morphology, similar to what has been reported in the literature. 54,55 Then, we performed EQE EL measurements and determine ΔV nr for the devices processed with CB and CF (Figure 4d and Table 2). From the EQE EL measurements, we noted that under the AM1.5 illumination intensity, the ΔV nr of the devices processed with CB and CF are also similar, which are 0.19 and 0.20 V, respectively.…”

The Asymmetric Strategy of Small‐Molecule Materials for Organic Solar Cells

“…The initial purpose of alkyl chain in OSCs materials is to supply the property of solution processibility. However, with the advancement of research, it has been discovered that the insulated alkyl chains not only affect solubility but also significantly alter the crystallization, stacking, and interactions of molecules, [120][121][122][123][124][125][126][127][128][129][130][131] thereby influencing charge transfer ability. This made the adjustment of alkyl chains an effective optimization strategy, particularly in the asymmetric regulation of alkyl groups.…”