Sidechain‐Engineered N‐PDIs Processed from Ethyl Acetate as Effective Cathode Interlayers for Organic Solar Cells

Abstract

Solution-processable organic solar cells (OSCs) have the potential to offer a source of low-cost renewable energy with low-energyintensive processing, have lightweight and flexible features, and power conversion efficiency (PCE) values of 19%. [1,2] The most efficient OSC devices are based on the bulk heterojunction (BHJ) structure composed of nanoscale intermixed continuous networks of an electron-donating conjugated polymer and a nonfullerene electron-accepting small molecule, together with anode and cathode interlayers (CILs) to improve charge carrier transport and collection in the device. [3,4] In bottom-anode top-cathode device configuration, PEDOT:PSS is the most common anode interlayer, which is deposited on top of the indium tin oxide (ITO) transparent electrode. In this configuration, the CIL would therefore be deposited on top of the organic BHJ to modify the electrode work function, such that OSC device performance would be increased as a result of the energy barrier between the metal electrode and the active layer being decreased. [5][6][7][8] To date, organic compounds have been widely applied as interlayers, and benchmark CILs for conventional OSC structure utilize the PFN-Br polymer [9] and small molecules based on perylene diimide (PDI) derivatives, such as those with polar amino N-oxide groups (PDINO) [10] or aliphatic amine groups (PDINN). [11] The polar groups endow the molecules with good solubility in methanol, a processing solvent that does not destroy the underlying organic photoactive layer. [4] In terms of better reproducibility, reduced synthetic steps, and well-defined structures, small-molecule interlayers exhibit intrinsic advantages over polymeric materials, which position PDI-based CILs as excellent candidates for future industrial applications of OSCs. [12,13] PDIs also have high electron mobility, strong optical absorption, suitable energy levels, and stability. [14] In addition, they can be easily functionalized to tune the work function of the electrode. [13,15] Through chemical modification, the electronic and morphological features of the applied PDI in the interlayer film can be adjusted to deliver better performance in the OSC device. Recently, some works featured the use of bay-substituted PDIs as CILs in OSCs. Wang et al. reported the synthesis of three bay-substituted PDIs and their application as CILs in OSCs, with performance of 16% when combined with PM6:Y6. [16] Our group also reported the use of PDI compounds containing NH groups functionalized at the bay region as an interlayer in OSCs, slot die coated from ethanol, with device performance above 10%. [17] Here, we present the application of a series of bay positionsubstituted N-annulated PDI derivatives as interlayers for OSCs. These N-PDIs possess well-defined structures and good film-forming ability on top of the organic photoactive layer,

A series of perylene diimide cathode interlayer materials for green solvent processing in conventional organic photovoltaics

“…However, in conventional OPVs, it is critical that the CIL is cast from a solvent that does not dissolve the bottom layers as keeping each layer discrete is crucial for device performance. Therefore, ethyl acetate as a processing solvent for the CILs is ideal as films of PM6:Y6 are highly solvent resistant to ethyl acetate, and because the CILs are coated onto of the BHJ in this case [ 19 ]. Furthermore, ethyl acetate is considered a green solvent due to its low toxicity and minimal associated hazards [ 20 , 22 , 29 ].…”

“…Some of the most widely used PDI materials for CILs are PDIN [ 14 ], PDINN [ 15 ], and PDINO ( Figure 1a ) [ 14 – 15 ]. Past work in our group has included N-annulated PDI materials, as seen in Figure 1b , where modifications to the PDIN-H CIL material include installation of a nitrile functional group on an open bay position for electrochemical tuning, and N-functionalization to provide several different side chains to study the impact of morphological changes on device performance [ 18 – 19 ]. With respect to the latter, we have introduced ethyl acetate as a suitable green solvent to process CILs onto high performance BHJs (e.g., PM6:Y6).…”

A fluorinated perylene diimide for polar and non-polar green solvent processed organic photovoltaic cathode interlayers

“…This loss was attributed to the partial dissolution of Y6 by ethyl acetate, as previously reported. 21 Notably, the absorption spectra of BHJ films after being coated with heptane or butanol did not show any decrease in absorption intensity (Fig. 4a and b).…”

Room-Temperature Photodeposited Amorphous VOx Hole-Transport Layers for Organic Devices

“…Additional results including FTIR spectroscopy, XRD, XPS fitting results, UPS spectra, XAS, AFM, UV−vis spectroscopy, and device characterization [16][17][18][19][20][21][22]25,68 (PDF) Dashed lines indicate the Fermi level. 53…”

“…Figure 4. Energy band diagram of OPV devices with VO x as HTL candidates and as-prepared (VO-AP) and annealed films (VO-250).Dashed lines indicate the Fermi level 53. …”