A star-shaped conjugated molecule featuring a triazole core and diketopyrrolopyrrole branches is an efficient electron-selective interlayer for inverted polymer solar cells

A novel triazole-cored, star-shaped, conjugated molecule (TDGTPA) has been synthesized for use as an electron-selective interlayer in inverted polymer solar cells (PSCs). This star-shaped molecule comprised a triazole unit as the central core, 2,5-thienyl diketopyrrolopyrrole units as π-conjugated bridges, and tert-butyl-substituted triphenylamine units as both end groups and donor units. The inverted PSC had the device structure indium tin oxide/ZnO/TDGTPA/poly(3-hexylthiophene) (P3HT)/fullerene derivative (PC(71)BM)/MoO(3)/Ag. Inserting TDGTPA as the electron-selective layer enhanced the compatibility of the ZnO-based electron transport layer and the P3HT:PC(71)BM blend-based photoactive layer. The low energy of the lowest unoccupied molecular orbital (−3.98 eV) of TDGTPA was favorable for electron transfer from the photoactive layer to the ZnO layer, thereby enhancing the photovoltaic performance of the PSC. The photo-conversion efficiency of the device incorporating TDGTPA as the electron-selective layer was 15.8% greater than that of the corresponding device prepared without it.