Modulation of Orbital Energy Levels of Tetrabenzoporphyrin toward Increased Open-Circuit Voltage and Possibility as n-Type Material in Organic Solar Cells

摘要

Tetrabenzoporphyrin (BP) is an organic p-type molecular semiconductor having a large π-conjugated system which can form effective charge-carrier paths in the solid state. However, BP has a poor solubility in any solvents, making its processing by cost-effective solution-based techniques quite difficult. This problem has been evaded via a “thermal precursor approach” in which a soluble precursor 1,4:8,11:15,18:22,25-tetraethano-29H,31H-tetrabenzo[b,g,l,q]porphyrin (CP) is solution-deposited then thermally converted to BP by in situ retro-Diels–Alder reaction (Scheme 1a) . By taking advantage of this approach, power conversion efficiencies (PCEs) of over 5% have been achieved with BP or its derivatives. However, the open-circuit voltage (V_(OC)) in these devices is relatively low because of the high energy level of the highest occupied molecular orbital (HOMO) of BP.