Design of a New Small‐Molecule Electron Acceptor Enables Efficient Polymer Solar Cells with High Fill Factor

Abstract

Improving the fill factor (FF) is known as a challenging issue in organic solar cells (OSCs). Herein, a strategy of extending the conjugated area of end-group is proposed for the molecular design of acceptor-donor-acceptor (A-D-A)-type small molecule acceptor (SMA), and an indaceno[1,2-b:5,6-b']dithiophene-based SMA, namely IDTN, by end-capping with the naphthyl fused 2-(3-oxocyclopentylidene)malononitrile is synthesized. Benefiting from the π-conjugation extension by fusing two phenyls, IDTN shows stronger molecular aggregation, more ordered packing structure, thus over one order of magnitude higher electron mobility relative to its counterpart. By utilizing the fluorinated polymer (PBDB-TF) as the electron donor, the corresponding device exhibits a high efficiency of 12.2% with a record-high FF of 0.78, which is approaching the theoretical limit of OSCs. Compared with the reference molecule, such a high FF in the IDTN system can be mainly attributed to the more ordered π-π packing of acceptor aggregates, higher domain purity and symmetric carrier transport in the blend. Hence, enlarging the conjugated area of the terminal-group in these A-D-A-type SMAs is a promising approach not only for enhancing the electron mobility, but also for improving the blend morphology, and both of them are conducive to the fill-factor breakthrough.

Key Parameters Requirements for Non‐Fullerene‐Based Organic Solar Cells with Power Conversion Efficiency >20%

“…For this simulation, we set the active layer bandgap at the optimal value of 1.7 eV for the donor and 2 eV for the NFA while assuming equal hole and electron mobilities (μ h = μ e ) for both material components. [4,13,40] It can thus be inferred from the simulations that an excellent tolerance to layer thickness variation can easily be established for μ ≥ 10 −3 cm 2 V −1 s −1 . Figure 5a displays the predicted PCE for NFA OPVs as a function of charge carrier mobility (μ = μ h = μ e ) and active layer thickness (see also Figure S8 (Supporting Information) for other important figures of merit).…”

“…For all devices we assume that the work functions of the electrodes/ interlayers are well aligned with the corresponding energy levels of the BHJ layer ( Figure 1a) and form Ohmic contacts. [22,40] Using the aforementioned μ h , μ e , k, IQE, optical constant, and layer thickness values as the input parameters, our simulations predict that single-junction NFA OPV cells may yield PCE values in excess of 18% (Figure 4a). The latter assumption and values are in line with recently reported data for the state-of-the-art NFA-based OPVs (see Table 2).…”

A High‐Efficiency Organic Solar Cell Enabled by the Strong Intramolecular Electron Push–Pull Effect of the Nonfullerene Acceptor

“…[17][18][19][20] From the aspect of device performance, the most impressive feature of NF-OSCs is the www.advmat.de www.advancedsciencenews.com been successfully demonstrated. [42][43][44][45] However, when the ICT effect is changed, there still should be other variable factors affecting their photovoltaic properties, and the investigation of the correlations between these factors and device performance will be of great importance to the molecular design of the photoactive materials.…”

Dithieno[3,2‐b:2′,3′‐d]pyrrol Fused Nonfullerene Acceptors Enabling Over 13% Efficiency for Organic Solar Cells

“…Designing the narrow bandgap acceptors with NIR absorption matching with mid-bandgap donors could be an ideal case for further improving the PCEs of OSCs. Recently, nonfullerene acceptors (NFAs) [4][5][6][7][8][9][10][11][12] used in OSCs have drawn vigorous attention A new electron-rich central building block, 5,5,12,12-tetrakis(4-hexylphenyl)indacenobis-(dithieno[3,2-b:2′,3′-d]pyrrol) (INP), and two derivative nonfullerene acceptors (INPIC and INPIC-4F) are designed and synthesized.…”