May 10, 2022 Aqueous Processing of Low-Band-Gap Polymer Solar Cells

Aqueous nanoparticle dispersions of a series of three low-band-gap polymers and poly[2,3-bis-(3-octyloxyphenyl)qui-noxaline-5,8-diyl-alt-thiophene-2,5-diyl] (P3) were prepared using ultrasonic treatment of a chloroform solution of the polymer and [6,6]-phenyl-C 61 -butyric acid methyl ester ([60]PCBM) mixed with an aqueous solution of sodium dodecylsulphate (SDS). The size of the nanoparticles was established using small-angle X-ray scattering (SAXS) of the aqueous dispersions and by both atomic force microscopy (AFM) and using both grazing incidence SAXS (GISAXS) and grazing incidence wide-angle X-ray scattering (GIWAXS) in the solid state as coated ﬁ lms. The aqueous dispersions were dialyzed to remove excess detergent and concentrated to a solid content of approximately 60 mg mL (cid:1) 1 . The formation of ﬁ lms for solar cells using the aqueous dispersion required the addition of the nonionic detergent FSO-100 at a concentration of 5 mg mL (cid:1) 1 . This enabled slot-die coating of high quality ﬁ lms with a dry thickness of 126 ( 19, 500 ( 25, and 612 ( 22 nm P1, P2, and P3, respectively for polymer solar cells. Large area inverted polymer solar cells were thus prepared based on the aqueous inks. The power conversion e ﬃ ciency (PCE) reached for each of the materials was 0.07, 0.55, and 0.15% for P1, P2, and P3, respectively. The devices were prepared using coating and printing of all layers including the metal back electrodes. All steps were carried out using roll-to-roll (R2R) slot-die and screen printing methods on ﬂ exible substrates. All ﬁ ve layers were processed using environmentally friendly methods and solvents. Two of the layers were processed entirely from water (the electron transport layer and the active layer). was repeated 4 times corresponding to a dilu- tion of the solution by a factor of 625. In the ﬁ nal step the suspensions were concentrated to have a solid content of 60 mg mL (cid:1) 1 . X-ray Scattering. TheSAXSandgrazingincidenceSAXS(GISAXS) experiments were performed at a laboratory setup using a rotating Cu-anode operating at 46 kV and 46 mA as X-ray source. The SAXS instrument was configured for a fully evacuated sample to detector distance of 4579 mm covering a q -range of 2.5 (cid:3) 10 (cid:1) 3 < q < 0.12 Å (cid:1) 1 , where the length of the scattering vector q = 4 π sin( θ )/ λ , with θ equal to half the scattering angle, and λ being the X-ray wavelength for Cu K R (1.5418 Å). The X-rays are monochromated and collimated by two-dimensional multilayer optics and detected by a 2D “ Gabriel ” -typegas-proportional delaylinedetector. 18 Thenano- particle dispersions were measured in 1 mm borosilicate capillaries, sealed with epoxy glue for the SAXS experiments, and GISAXS of films spin-coated on glass were measured by orienting the substrate at an X-ray incidence angle of 0.5 (cid:1) . The 2D scattering images of the randomly oriented particles in dispersion were reduced to 1D cross sections by azimuthal averaging, whereas the GISAXS scattering were reduced to 1D curves by taking projections through the Yoneda peak 18 at constant q z . The reduced 1D data were analyzed by using the Bayesian inverse Fourier transform (BIFT). 19