Impact of the solubility of organic semiconductors for solution-processable electronics on the structure formation: a real-time study of morphology and electrical properties

Abstract

The control of structure formation in the active layers of organic solar cells allows for improvement in their processability and enhancement of the efficiency of the final devices. In the present work, in situ studies of film formation from binary toluene solutions of an electron donor, poly(3-hexylthiophene) (P3HT), and an electron acceptor such as [6,6]-phenyl-C-61-butyric acid methyl ester (PCBM) or indene-C60 bisadduct (ICBA) have been conducted. These experiments were carried out using GIWAXS with simultaneous electric current measurements. The comparative analysis of the intensity of the amorphous halo, and the 100 and 020 peaks of P3HT reveals the development of the semicrystalline morphology of the donor through a partly-ordered phase. The experiments show the impact of the chemical structure of the acceptor, as well as that of the donor : acceptor ratio on the kinetics of drying and crystallization. The optimal bulk heterojunction morphology was achieved for P3HT : ICBA 1 : 1, which exhibited the highest value of current. A more efficient phase separation in non-annealed P3HT:ICBA films as compared to P3HT:PCBM was accounted for by the differences in solubility of the components in toluene. The structure formation during solvent evaporation can be subdivided into three stages, including the ordering of the polymer in solution, phase separation during precipitation, and the perfectioning of P3HT crystals in the dry film.

Real‐Time Study on Structure Formation and the Intercalation Process of Polymer: Fullerene Bulk Heterojunction Thin Films

“…OPV BHJ film morphology evolves over a series of periods during its formation upon drying from dilute solutions . The progressive increase in the components’ concentration in the solvent is one of the reasons of this multiperiod film formation . Throughout the course of active layer formation, the concentration of the donor and acceptor increases up to a critical value called solubility limit, at which the corresponding component might start to precipitate .…”

“…Therefore, the phase separation was considered to be driven by P3HT crystallization . Three main film formation periods, before reaching the final film morphology (glassy state), have been identified:…”

In Situ Coupling Applied Voltage and Synchrotron Radiation: Operando Characterization of Transistors

“…The structural evolution of the polymer: fullerene active layers during the drying process give insight of the microstructure formation linked to the optimization of the solar cells [ 26 ]. Moreover, the solution processing and the microstructure formation can be coupled with electrical response of the active layers [ 27 , 28 ]. Usually scattering X-ray signal is rather weak in solution phase and at the initial stage of the microstructure formation and such studies would be impossible to realize without usage of synchrotron radiation.…”

Direct Observations of the Structural Properties of Semiconducting Polymer: Fullerene Blends under Tensile Stretching

“…There are a lot of scientific efforts aimed at understanding and improving the microstructure of polymer-based OSCs, such as solution optimization [22,23], employing low volatile additives [24][25][26] and thermal annealing [27]. Moreover, the direct observation of film crystallization/formation during solvent evaporation gives insight into the phase separation in blends and allows correlating observed phenomenon to electrical properties [28], thus controlling polymer chain crystallization and fullerene molecule aggregation as a function of the blend concentration. In parallel, several methods have been developed with compact instrumentations, capable of tracking the crystallization process of semiconducting polymers and blends at synchrotron radiation facilities [8,[29][30][31] Taking into account this tremendous progress in understanding the structural evolution during the solution processing [31,32], the development of flexible and intrinsically stretchable organic conductors is very promising for the realization of emerging novel devices [33].…”