Enhancement of efficiency in organic photovoltaic devices containing self-complementary hydrogen-bonding domains

Abstract

Self-complementary hydrogen-bonding domains were incorporated as the electron deficient unit in "push-pull", p-type small molecules for organic photovoltaic active layers. Such compounds were found to enhance the fill factor, compared with similar non-self-organized compounds reported in the literature, leading to higher device efficiencies. Evidence is presented that the ability of these molecules to form one-dimensional hydrogen-bonded chains and subsequently exhibit hierarchical self-assembly into nanostructured domains can be correlated with improved device efficiency.

Keywords: hydrogen-bonding; organic photovoltaics; self-assembly.

Figure 1

N-ethylhexyl-substituted (1) [20] and target free N–H (2) cyanopyridone structures.

Scheme 1

Synthesis of the cyanopyridone 2, reagents and conditions: (i) Pd(PPh₃)₄, Cs₂CO₃, toluene, reflux, 16 h, 84%; (ii) EtOH, reflux, 2 h, 82%.

Figure 2

(a) Chloroform (solid line) and thin-film (dashed line) UV–vis absorption and emission spectra and (b) optimized DFT structure and calculated orbital densities of compound 2.

Figure 3

The concentration dependence of (a) the NH ¹H NMR chemical shift and (b) the vinyl proton chemical shift for compound 2 in d₆-benzene. The line is the regression fit of Equation 1 to the data.

Figure 4

AFM height image of observed nanostructures of films drop cast from (a) 10 mg/mL and (b) 1 mg/mL chloroform solution of 2.

Figure 5

Dimeric structures of 2. (a) centrosymmetric dimer of 2; (b) bond-rotated centrosymmetric dimer of 2 as predicted by DFT calculations.

Figure 6

Schematic representation of self-complementary interactions leading to one-dimensional chains.