EFFECT OF ADSORBED O-CHLORANIL ON THE SURFACE PHOTO-VOLTAGE OF METAL-FREE PHTHALOCYANINE FILMS

The surface photovoltage of metal-free phthalocyanine (H2Pc) films with known concentrations of adsorbed o-chloranil (o-CA) is reported, and monolayer coverages (≈1015 molecules/cm2) of o-CA result in the inversion of the sign of the photovoltage, an increase of approximately two orders of magnitude in the photovoltaic relaxation time, and a broadening of the phthalocyanine Q-band into the near IR. Higher coverages of o-CA resulted in samples with no photovoltage within the experimental detection limits. All of these observations are consistent with the formation of charge transfer complexes ( H2Pc+ o-CA-) at these surfaces, which results in the consequent alternate decay mechanism for the photoexcited H2Pc molecule: H2pc*+o-CA-→ kH2Pc++o- CA--, H2Pc*+o-CA--→ kH2Pc+o-CA-. The experimental evidence indicates that k-13 is less than 7 nsec and k-15 is roughly 0.6 msec for monolayer o-CA coverages. © 1979.