High Photoelectric Quantum Yield in Donor-Acceptor Bulk Heterojunction Organic Solar Cells

Reasons behind a higher photoelectric quantum yield in donor-acceptor organic solar cells (D-A--OSCs) than in one-component OSCs have been considered: (1) the appearance of an intense charge-transfer (CT) vibronic band in the absorption spectrum; (2) a change in the spectrum of CT states, in which the molecular exciton (ME) zone is located above the lowest charge-transfer state (LCTS); and (3) a longer lifetime of the LCTS as compared to the ME. Cause 1 makes it possible to select the optimal OCS absorption spectrum corresponding to the solar spectrum, and causes 2 and 3 eliminate the need for fast charge separation in the LCTS, for which the rate by ionization in the bulk heterojunction field is sufficient.