The effect of controllable thin film crystal growth on the aggregation of a novel high panchromaticity squaraine viable for organic solar cells

Phase separation, crystallinity and monomer-aggregate population control in solution processed small molecule solar cells

“…The thin film absorbance has two broader peaks at 556 nm and 656 nm. This substantial broadening is typical of analino squaraines (SQs) with linear side chains [22,27,30,31], and has often been attributed to the upper and lower Davydov components in SQ aggregates under the assumption of an oblique transition dipole alignment as part of a herringbone packing geometry [27,31,32]. However, such an interpretation is inconsistent with the single crystal structure of DHSQ(OH) 2 which exhibits a single molecule per unit cell with the conjugated backbones (and transition dipole moments) parallel to one another throughout the crystal [27].…”

“…It is the packing and morphology of the squaraines that leads to this broadening but, with multiple excited states accessible through crystallization, some aggregates may actually inhibit device performance because of energy level mismatch [20]. In fact, in recent work there has been significant confusion regarding the assignment of the excited states [21][22][23][24][25][26][27], with low energy absorption features typically being assigned to J-aggregates despite no observable fluorescence nor a crystal structure that would support Davydov splitting [28]. Despite an excellent description of the structure-property relationship in anilinic squaraines by Brück et al [27], we consider the excited states assignment to restrict future progress and we seek to fully correct that assignment herein.…”

Increasing H-aggregation of p-DTS(FBTTh2)2 to improve photovoltaic efficiency by solvent vapor annealing

“…In particular, the peak ratio decreases with bandwidth for H-aggregation and increases with bandwidth for J-aggregation [38e40]. The other was that red-shift absorption peak (compared to absorption peak of monomer) represented J-aggregation and the blue-shift one represented H-aggregation [22,26,41,42]. Each of the two viewpoints has its own merits.…”

“…H-and J-aggregates have their own intrinsic optical and electronic properties, determined by the interaction of transition dipole moments and Davydov splitting [26,27]. The absorption peaks of H-aggregation and J-aggregation are blue-shifted and red-shifted compared to those in isolated state, respectively [21,28,29].…”

Confirmation of the Origins of Panchromatic Spectra in Squaraine Thin Films Targeted for Organic Photovoltaic Devices

“…7 This strong panchromaticity coupled with high extinction coefficients (in excess of 10 5 L mol -1 cm -1 ) 8 offer huge potential for squaraine based organic photovoltaic (OPV) devices. [9][10][11][12] The benefits of squaraines lie far beyond their panchromaticity in the solid state however. The chemical space spanned by squaraine derivatives is vast, offering near endless possibilities for varying their structure to target more efficient prototypes which can be effectively mass produced.…”