Metal substituted metalloporphyrins as efficient photosensitizers for enhanced solar energy conversion

The electron transfer dynamics of tetra(4-carboxyphenyl)porphyrin with different central metal ions Fe(III), Cu (II), Co(II),Ni(II), Zn(II) adsorbed on ZnO nanorods have been investigated by using photophysical and electrochemical studies. Spectroscopic studies confirmed that metalloporphyrins anchored onto ZnO through the carboxylic group. XPS studies indicated that replacement of free base porphyrin with different metals resulted in change in symmetry with uniform distribution of electron density of nitrogen atom of pyrrole ring which gives one broad peak of N1S state. Absorption studies revealed the bathochromic shift of soret band in ZnO-TCPPM nanocomposites as compare to free base porphyrin and metalloporphyrins owing to the electronic coupling between ZnO and TCPPM which stabilize the pi* orbital. The photoluminescence properties of metalloporphyrins are shown to be highly dependent on central metal atom. Steady state and PL lifetime measurements studies shows the electron transfer in ZnO-TCPPM occurred feasibly for TCPPZn sensitizer as Zn(II)porphyrin have long lived excited state as compare to other metalloporphyrins. Improved photovoltaic properties of the metalloporphyrins are originated from electron injection driving force from dye to ZnO. Introduction of metal in porphyrin cavity increase the electron transfer process. Incase of TCPPCo, TCPPNi fast recombination exists between metal cation and photogenerated electron that inhibits the photocurrent generation. J-V Characteristics revealed there is 4.5 fold increases in efficiency for ZnO-TCPPM device as compare to device composed of free base porphyrin.