Determination of phase diagrams of binary and ternary organic semiconductor blends for organic photovoltaic devices

Ternary blends were recently suggested as a sound approach to increase the short circuit current density of organic solar cells by sensitizing the bulk heterojunction (BHJ) with a further absorber, i.e., a low band gap polymer. Poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b´]dithiophene)-alt-4,7(2,1,3-benzothiadiazole)] (PCPDTBT) is a suitable candidate as low band gap polymer for ternary blends with poly(3-hexylthiophene) (P3HT) and [6,6]-pheny-C61-butyric acid methyl ester ([60]PCBM) due to its ideal energy level and charge carrier properties. Phase diagrams are common in polymer science to visualize the mixing behavior of multicomponent systems as a function of temperature. In this study, we have used differential scanning calorimetry (DSC) to extract phase diagrams for binary and ternary organic semiconductor blends, and built the corresponding solar cells to analyze correlations between the thermal and the electrical properties of such semiconductor blends.

Figure optionsDownload as PowerPoint slideHighlights
► We use DSC to determine the phase behavior of the P3HT/PCPDTBT/[60]PCBM blends.
► The phase diagrams of binary as well as ternary blends are constructed.
► The phase behavior of blends correlates well with their electric properties in cells.
► The solar cells from amorphous ternary composites have poor electrical performance.