Bilayer- and bulk-heterojunction solar cells using liquid crystalline porphyrins as donors by solution processing

Bilayer- and bulk-heterojunction solar cells based on liquid crystalline porphyrins (donors) were fabricated by solution processing. These porphyrins are (i) highly absorptive over the wavelengths of the solar spectrum, (ii) having energy levels matched well with the electron acceptors and anode materials to facilitate charge separation and transfer, and (iii) of a unique homeotropically aligned architecture for efficient charge transport and light harvesting. Thermal annealing of these solar cells induced alignments of porphyrins in the photoactive layers, leading to a factor of 4–5 higher power conversion efficiencies and short circuit current densities than their counterpart devices without postannealing.