PHOTOINDUCED UNIDIRECTIONAL ELECTRON-TRANSFER IN A PORPHYRIN HETEROJUNCTION

Organic heterojunctions made by deposition of two different types of p orphyrins onto an ITO substrate by electro-polymerisation and spin-coa ting exhibit rectification upon illumination. The redoxpotentials for the various porphyrin D/A combinations can be varied by using differen t porphyrin metal centers. Different exothermicities for photo-induced electron-transfer in this way results in different values of the shor t circuit current. Depending on layer thickness and type of porphyrins , the open circuit voltage is less than or equal to - 0.4 V and the in cident photon to current efficiency is 2.5% at 440 nm. Possible mechan isms for the observed rectification are discussed.