A mechanistic investigation of morphology evolution in P3HT–PCBM films induced by liquid crystalline molecules under external electric field

Abstract

We demonstrate that the morphology of poly(3-hexyl thiophene) and [6,6]-phenyl-C61-butyric acid methyl ester (P3HT-PCBM) bulk heterojunctions (BHJ) could be tuned by the 4-cyano-4'-pentylterphenyl (5CT) liquid crystalline molecules under electric field assisted treatment for enhanced solar cell performance. The miscibility and interactions between the components were carefully studied, showing that 5CT could induce the crystallization of P3HT to form edge-on structures in ternary blends after electric field assisted treatment as revealed by grazing-incidence wide-angle X-ray diffraction (GIXRD). The PCBM and 5CT are supposed to form the rod-like complexes, and the nanorods could orient to the direction of electric field, accompanied by the homogeneous distribution of nanorods in diameters of about 30 nm at an electric field of 600 V mm(-1). The sizes of PCBM clusters and complexes are dependent on the 5CT doping ratios and intensity of electric field according to grazing-incidence small-angle X-ray scattering (GISAXS) analysis. When the active layers were processed under the atmospheric environment, the power conversion efficiency (PCE) could reach 3.5% at 5CT weight fraction of 6 wt% after treatment by an electric field of 600 V mm(-1), in contrast to the PCE value of 2.4% for a pristine P3HT-PCBM blend. This work provides an attractive strategy for manipulating the nanostructure of BHJ layers and also increases insight into morphology evolution when liquid crystalline molecules are incorporated into BHJs.

Versatile third components for efficient and stable organic solar cells

“…Some of the nonvolatile small molecule additives were used to control the horizontal and vertical phase separation. [262][263][264][265][266][267][268][269][270][271][272][273][274][275][276] As some representative examples, Kim et al 262 employed a fractional amount of nonvolatile additives (a) in P3HT/PC 61 BM blend and the PCE was improved. This additive selectively partitioned into P3HT due to its special hydrophobicity, and effectively enhanced phase separation between the electron donor and acceptor phases.…”

Pressure effects on interfacial surface contacts and performance of organic solar cells

“…The (100), (200), and (300) peaks positions are associated with the out-of-plane and the dominant peak in the in-plane was the (010). Prior work 29,[31][32][33][34][35] has shown that P3HT chains preferentially align themselves in the edge-on configuration with the p-p stacking in the (010) direction. Therefore, with the application of pressure in the out-of-plane direction and perpendicular to the substrate, the bonds between the polymer backbones are also elongated in the in-plane direction leading to the edgeon configuration.…”

Synergistic Effects of Morphological Control and Complementary Absorption in Efficient All-Small-Molecule Ternary-Blend Solar Cells

“…A thiophene-containing small molecule has been found to act as a nucleating agent to improve the conformation of polymer chains and enhance their crystallinity. 49 Accordingly, we conclude that BDT6T, a small molecule containing thiophene units, could function as a morphology controller, inducing a favorable active layer morphology with interpenetrating nanoscale domains. Figure S5 shows AFM images (tapping mode) with higher resolution for different conditions.…”