Tuning the Color Palette of Semi-Transparent Solar Cells via Lateral ??-Extension of Polycyclic Heteroaromatics of Donora??Acceptor Dyes

摘要： Durable solar cells with tunable color and diaphaneity are very promising for building integrated photovoltaic applications. In this paper we employ donor–acceptor organic dyes U3, U4, U5, and R6 featured by polycyclic heteroaromatics 6,12-dihydroindeno[1,2-b]indeno[2',1':4,5]thieno[2,3-d]thiophene (IT2), 7,15-dihydrobenzo[6',7']indeno[2',1':4,5]thieno[3,2-b]benzo[6,7]indeno[2,1-d]thiophene (BIT2), 7,15-dihydrophenaleno[1,2-b]phenaleno[2',1':4,5]thieno[2,3-d]thiophene (PT2), and 9,19-dihydrobenzo[1',10']phenanthro[3',4':4,5]thieno[3,2-b]benzo[1,10]phenanthro[3,4-d]thiophene (BPT2) to fabricate semi-transparent dye-sensitized solar cells (DSSCs). The U3, U4, U5, and R6 based cells are goldenrod, crimson, red, and sapphire blue, with power conversion efficiencies of 3.5%, 8.2%, 7.6, and 10.1% at the AM1.5G conditions. Density functional theory calculation and voltammetric measurement reveal that lateral π-extension of polycyclic heteroaromatic brings forth a downward displacement of lowest unoccupied molecular orbital, affording a high molar extinction coefficient, low-energy gap blue dye. Femtosecond fluorescence decay measurements of dyed titania and alumina films unravel the electron injection yields of photo-excited dye molecules, which are well correlated with the maximal values of external quantum efficiencies of DSSCs. After 1,000 h full sunlight soaking at 60 oC, the red and blue DSSCs exhibit stable photocurrents, owing to the strong bonding and photochemical stability of dye molecules adsorbed on the surface of titania as well as the retention of close-to-unity electron collection yield.