Impact of Alkyl Chain Length on Small Molecule Crystallization and Nanomorphology in Squaraine-Based Solution Processed Solar Cells

Abstract

In this work, we have investigated a series of aniline-based squaraines, with varying solubilizing alkyl chains, as donor materials in bulk heterojunction (BHJ) solar cells. Although these squaraine molecules exhibit similar absorbance spectra and crystal structures, the difference in properties that drive the OPV performance becomes apparent when each squaraine is blended with PCBM. Thin film X-ray diffraction results demonstrate a disruption of squaraine crystallization in the presence of PCBM, more so for shorter side chain squaraines. As a result, the hole mobilities of BHJ films of shorter side chain squaraines show the largest drop when compared to their neat films, whereas the mobility decrease for the longer side chain counterparts is small. However, morphological studies have shown that the phase separation rapidly happens during the spin-casting process for longer side chain squaraines. Ultimately, it is the extent of phase separation that dominates the final device efficiency. Therefore, rational design can greatly be influenced as a result of our systematic materials properties overview for anilinic squaraines targeted for OPV.

In Situ Studies of Solvent Additive Effects on the Morphology Development during Printing of Bulk Heterojunction Films for Organic Solar Cells

“…In contrast, the peak position remains almost unchanged until 400 s. In stage III, it shifts to smaller q values indicating that the lattice distance of polymer crystallites becomes larger, which could be caused by stretching of alkyl chains after solvent evaporation. [45,46] In the late stages IV and V, also the formed crystal do not undergo a further compaction.…”

A Novel Strategy for Scalable High‐Efficiency Planar Perovskite Solar Cells with New Precursors and Cation Displacement Approach

“…The reason is that the precursors MAI and PbI 2 have strong tendency towards the crystallization of MAPbI 3 in the film formation. Different from the MAI, the PAI with a long alkyl chain could effectively delay the crystallization of the precursor PAPbI 3 film in the deposition, favoring homogeneous nucleation and film formation with high coverage . Experimentally, the thicknesses of the final MAPbI 3 perovskite layers, which ranged from ≈200 to ≈800 nm, can be adjusted at the stage of coating the precursor PAPbI 3 film by controlling the precursor concentrations and putting rates (Figure S5, Supporting Information).…”

Effect of Sodium Hydroxide Pretreatment of NiOx Cathodes on the Performance of Squaraine‐Sensitized p‐Type Dye‐Sensitized Solar Cells

“…The length of the alkyl substituents in squaraines is known to affect their solubility in organic solvents and their tendency to form aggregates when the squaraines are chemisorbed on oxide surfaces. Beside the analysis of the performance of the p‐DSSCs sensitized with O4_C4 and O4_C12 in this work we also explore the influence of NiO x surface pretreatment with NaOH prior to the step of electrode sensitization.…”