Silaindacenodithiophene‐Based Low Band Gap Polymers – The Effect of Fluorine Substitution on Device Performances and Film Morphologies

Abstract

Silaindacenodithiophene is copolymerized with benzo[c][1,2,5]thiadiazole (BT) and 4,7‐di(thiophen‐2‐yl)benzo[c][1,2,5]thiadiazole (DTBT), respectively their fluorinated counter parts 5,6‐difluorobenzo[c][1,2,5]thiadiazole (2FBT) and 5,6‐difluoro‐4,7‐di(thiophen‐2‐yl) benzo[c][1,2,5]thiadiazole (2FDTBT). The influence of the thienyl spacers and fluorine atoms on molecular packing and active layer morphology is investigated with regard to device performances. bulk heterojunction (BHJ) solar cells based on silaindacenodithiophene donor‐acceptor polymers achieved PCE's of 4.5% and hole mobilities of as high as 0.28 cm2/(V s) are achieved in an organic field‐effect transistor (OFET).

Charge Separation in Intermixed Polymer:PC70BM Photovoltaic Blends: Correlating Structural and Photophysical Length Scales as a Function of Blend Composition

“…The absorption of the films agrees with previously published spectra and is included in the supporting information (SI). 20 The SiIDT-DTBT photoluminescence is very strongly quenched in all blends reaching ~ 98 % for the 4:1 blend and > 99% for all others. Such high yields of quenching are consistent with the morphological picture built by our TEM analysis and confirms that SiIDT-DTBT and PC70BM are highly miscible and tend to form an intimately mixed polymer:fullerene phase instead of pure polymer domains even in blends with 80 % polymer.…”

“…This result is consistent with the highly amorphous nature of SiIDT-DTBT, which shows no clear signatures of pi-pi or lamellar stacking in wide-angle X-ray scattering measurements of un-annealed as cast films. 20 The TEM images of the 1:2 and 1:4 blends are however much coarser, consisting of contrasting dark and bright patches, indicating the separation of fullerene-rich domains (dark areas) out of the intermixed phase. 40 The fullerene domains appear with approximate diameters of ~ 1.7 nm and 4 nm in the 1:2 and 1:4 blend respectively (as estimated from the TEM images).…”

“…SiIDT-DTBT (see figure 1) is representative of a range of relatively amorphous indacenodithiophene based polymers which have been shown to be highly miscible with PC70BM, while still sustaining efficient photocurrent generation in optimal, typically 1:3, blend compositions. 20 In the present study, blends with different compositions were fabricated to allow us to study the impact of film nano-structure on the charge generation dynamics. In particular, employing this approach, we investigate whether photophysical descriptions of charge separation determined the highly crystalline model blend system pBTTT:PCBM 15,17,37-39 can be extended to an amorphous blend more representative of many technologically relevant OPV blends, and determine in particular the relevant structural and photophysical length scales in this amorphous blend which determine the efficiency of charge separation.…”

“…6,8,[10][11][12][13][14][15][16][17][18][19] In this study, we address this issue for blend films and devices employing an amorphous donor polymer silaindacenodithiophene donor (SiIDT-DTBT) previously shown to exhibit high miscibility with PC60BM. 20 Our study employs a range of blend ratios to modulate the blend morphology and both rigorous structural and spectroscopic characterization allowing us to quantitatively analyse the correlations between blend structure and device performance.…”

Noncovalent Interactions in Organic Electronic Materials

“…[84][85][86] Fluorination has been carried out on a wide variety of building blocks used in the synthesis of polymers, including thiophenes, carbazoles, thienothiophenes, benzothiadiazoles, benzotriazoles, benzodithiophenes, indacenodithiophenes, and anthradithiophenes. [87][88][89][90][91][92][93][94][95][96] Recently, we have shown The idea of attaching bulky substituents has also been widely used to control the packing of small molecules. [101][102][103] In particular, attaching bulky triisopropylsilyl (TIPS) groups via ethynyl linkers to the periphery of pentacene triggers the herringbone packing configuration of pentacene to transform into a 2D-brickwork packing arrangement.…”