Impact of helical organization on the photovoltaic properties of oligothiophene supramolecular polymers† †Electronic supplementary information (ESI) available: Synthesis and characterization of 3 and 4, UV-vis spectra, solar cell device properties and AFM images. See DOI: 10.1039/c7sc05093c

Higher order structures of semiconducting supramolecular polymers have a huge impact on their BHJ-OPV device performance.


Materials and Methods
Column chromatography was performed using 63-210 m silica gel. Preparative gel permeation chromatography (GPC) was performed on a recycling preparative HPLC (LC-9225NEXT, Japan Analytical Industry) equipped with GPC columns JAIGEL-1H + 2H). All other commercially available reagents and solvents were of reagent grade and used without further purification. The solvents for the preparation of the assemblies were all spectral grade and used without further purification. 1  Molecular mechanics calculations were performed on MacroModel version 10.4 using AMBER* force field. UV-vis spectra were recorded on a JASCO V660 spectrophotometer. Differential scanning calorimetry (DSC) was performed on SII DSC6220.

Scanning tunneling microscopy (STM)
1-Phenyloctane (98%, Aldrich) solutions of 3 and 4 were prepared at different concentrations. A droplet of these solutions was then deposited on a graphite substrate. STM imaging of the samples was performed at the liquid-solid interface using a Pico-SPM (Molecular Imaging, Agilent Technology) scanning tunneling microscope. Cut Pt/Ir tips were used to obtain constant current images at room temperature with a bias voltage applied to the sample. STM images were processed and analyzed using the application FabViewer. 1

Fabrication of organic solar cells
Bulk heterojunction solar cell devices were fabricated on indium-tin oxide (ITO) coated glass. The ITO glass substrates were subsequently cleaned with acetone and 2-propanol in ultrasonic bath. The resultant ITO substrates were then exposed to UV-ozone for 20 min and coated with PEDOT:PSS [poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate)](AI 4083, thickness: ca. 30 nm). The

S3
substrates were heated for 20 min at 120 °C to remove residual water. In a N2 glove box, 0.5 mL of chloroform solutions containing PC71BM (2.5 mg, Luminescence Technology Corp., Taiwan Province) and oligothiophene derivatives (2.5 mg) were spin-coated (1000 rpm for 30 s) onto the substrate. The thicknesses of the resulting BHJ films were determined to be 90-120 nm for

Hole mobility measurements
Hole mobilities of 3:PC71BM and 4:PC71BM (prepared from 10 mg mL -1 CHCl3 solutions) without and with SVA using CS2 were estimated by the charge-only space-charge limited current (SCLC) method. The SCLC is described by J = 9ε0εrμV 2 /8L 3 , where J is the current density, L is the film thickness of the active layer,  is the hole mobility, εr is the relative dielectric constant of the transport medium, ε0 is the permittivity of free space (8.85 × 10 -12 F m -1 ), V is the applied voltage to the device. SCLC measurements were carried out with a device structure of ITO/MoO3/active layer/MoO3/Al by taking the current density in the range 0-10 V and fitting the results to a space-charge limited form.

Synthesis and Analytical Data
Compound 3 and 4 were synthesized according to Scheme S1. The syntheses of reference compounds 1 and 2 were reported previously. 2 atmosphere. After 1 h, SnBu3Cl (1.50 g, 4.61 mmol) was added and the mixture was stirred for 30 min. The reaction mixture was warmed to r.t., and further stirred overnight. The reaction mixture was poured into water, and evaporated to remove THF. The resulting mixture was extracted by CHCl3, and washed twice with water. The organic layer was dried with Na2SO4, filtered and evaporated to dryness to give compound 6 as light yellow liquid (2.49 g). This compound was used for the following reaction without purification.
S5 5'-Bromo-3,4'-dibutyl-2,2'-bithiophene (7): To an ice-cooled 2:1 CHCl3/acetic acid mixture (30 mL) containing 5 (750 mg, 2.69 mmol), N-bromosuccinimide (478 mg, 2.69 mmol) was added in three portions at interval of 10 min. The reaction mixture was warmed to r.t. and stirred for 3 h. The resulting mixture was diluted with CHCl3, and washed twice with sat. aq. NaHCO3. The organic layer was dried with Na2SO4, filtered and evaporated to dryness to give compound 7 as light yellow liquid (934 mg, 97%). 1  was stirred at -78 °C for 1 h under N2 atmosphere. After 1 h, SnBu3Cl (405 mg, 1.24 mmol) was added and the mixture was stirred for 30 min. The reaction mixture was warmed to r.t., and further stirred overnight. The reaction mixture was poured into water, and evaporated to remove THF. The resulting mixture was extracted by CHCl3, and washed twice with water. The organic layer was dried with Na2SO4, filtered and evaporated to dryness to give compound 10 as yellow liquid (2.49 g). This compound was used for the following reaction without purification. The reaction mixture was cooled to r.t., diluted with ethyl acetate, and then washed twice with water.

Note:
The sharp diffraction at d = 3.91 nm, which is accompanied by the higher order diffractions at d = 1.98 and 1.30 nm, cannot be assigned at the moment. Because the intensities of these diffraction peaks differ by samples, they do not arise from the structural rearrangement of 4. They may rather arise from certain ordering of PC71BM upon co-aggregation with highly crystalline 4. S14 Fig. S6. (a,b) Normalized UV-vis spectra of thin films of (a) 3 (dashed curve, c = 5 mg mL -1 ) and 3:PC71BM (solid curve, ctotal = 10 mg mL -1 ), and (b) 4 (dashed curve, c = 5 mg mL -1 ) and 4:PC71BM (solid curve, ctotal = 10 mg mL -1 ).