Real-time X-ray scattering studies of film evolution in high performing small-molecule–fullerene organic solar cells

Abstract

Comprehensive studies of the influence of the formulation additive 1,8-diiodooctane on the structural evolution of small molecule BHJ films with GIWAXS and GISAXS are presented.

Comparison of the Morphology Development of Polymer–Fullerene and Polymer–Polymer Solar Cells during Solution‐Shearing Blade Coating

“…More recently, Richter and DeLongchamp et al used real-time X-ray diffraction to understand the solvent additive effect in polymer:fullerene and small-molecules:fullerene solar cells. [36,37] It has been shown that realtime X-ray diffraction is a powerful tool to track down the polymer crystallization during the drying process.…”

Real‐Time Photoluminescence Studies of Structure Evolution in Organic Solar Cells

“…This observation is consistent with the minor solution crystallization observed in our previous study. [ 56 ] The solubility limit for p-DTS(FBTTh 2 ) 2 in CB at the sample stage temperature of 40 °C has been estimated to be (45 ± 5) mg mL −1 . [ 24 ] In case of the BHJ without DIO the strong absorbance increase occurs at concentrations of (212 ± 59) mg mL −1 total solid content in solvent.…”

“…[ 23,54,55 ] The increased device performance for BHJs processed with DIO compared to fi lms prepared without DIO was attributed to the increased domain order, purity and domain sizes. [ 55 ] Addition of "large" amounts of DIO (e.g., volume fractions of 1%) was found to lead to excessive crystallization and domain coarsening [ 56 ] and subsequently device failure. In contrast to polymer-based BHJs, the extent of crystallization is not self-limited.…”

“…[ 39,57,58 ] In the case of p-DTS(FBTTh 2 ) 2 these aggregates show a strong preferential orientation distribution, leading to highly anisotropic samples with a preferential orientation of the molecule backbone parallel to the sample surface which was shown by previous X-ray studies where a pronounced series of (00l) peaks in the out-of-plane direction and high overall crystallinities were observed. [ 23,54,56 ] The extremely pronounced edge-on orientation distribution after the evaporation of the main solvent causes the absorbance at ≈2 eV to decrease from the solution to the dry state. This decrease in absorption with increased order is due to the specifi cs of p-polarized transmission under a comparably large incidence angle (≈56°) and might be a direct result of the reduced symmetry in the dry compared to the solution state.…”

“…[ 10,[13][14][15] The benefi cial morphology changes caused by the additives were originally attributed to selective solvation of the fullerene, [ 8 ] but recent studies have established that the working mechanisms for additives are far more diverse. [ 16,17 ] We and others have used in-situ grazing incidence X-ray diffraction (GIXD), grazing incidence small angle X-ray scattering (GISAXS), and optical studies to gain insight into the real-time structure evolution of spin-coated and blade-coated BHJs. [ 16,[18][19][20][21][22][23][24] It was shown that additives can impact the structure evolution of polymer-fullerene BHJs by decreasing the solvent quality and directly or indirectly plasticizing the crystallizing material, which generally results in higher crystallinity and a modifi ed nanometer-scale domain structure.…”