An investigation of surface photovoltaic properties of TiOPc and AlClPc

In this study, surface photovoltages of titanyl phthalocyanine (TiOPc) and chloroaluminum phthalocyanine (AlClPc) were explored using surface photovoltage spectrum (SPS) technique and field-induced photovoltage spectrum (FISPS) technique. The experimental results show that in the region of 300–800 nm both the metallophthalocyanines give two surface photovoltage response bands corresponding to Soret-band (300–420 nm) and Q-band (500–800 nm), respectively, with Bethe splitting of Q-band. It was experimentally confirmed that the two bands of TiOPc and AlClPc result from electron transition of the same type, π–π∗ transition. From the results of FISPS it was inferred that TiOPc has p-type character and AlClPc has n-type character. It is coincided with the result of the optimal phase of SPV response. Also it was found that the generation efficiency of photocarriers for TiOPc was nearly not affected by the alternation of the sign of the external electrical field. It is different from AlClPc. Since the precursor of photogenerated free carrier for TiOPc is known to be of charge-transfer state, this observation should be an indication that the precursor for AlClPc has an other than the charge-transfer state.