Dark and photovoltaic properties of doped tetraphenylporphyrin sandwich cells. Part 1.—Doping effects and dark electrical properties

Abstract

The effect of varying the central substituent of meso-tetraphenylporphyrin (TPP) on its interaction with electron-acceptor dopants in thin-film sandwich photovoltaic cells of the structure Al|Al₂O₃|TPP|Au has been investigated for iodine vapour and oxygen-water vapour dopants. Cells were fabricated, doped and tested under high vacuum without contact with the atmosphere, by measurement of open-circuit voltage, short-circuit current, current voltage characteristics and capacitance. A wide variation in behaviour towards iodine vapour is observed, with a trend of increasing affinity to the dopant and increasing device stability in the order of central substituent Mg > Zn > H₂ > Cu > Ni > Co. For the least stable compounds, the dopant is continually lost after fabrication, resulting in a deterioration of the photoresponse in parallel with an increase in resistance, decrease in capacitance and a change from a rectifying-type to an ohmic-type current-voltage characteristic. Current transport mechanisms are discussed for O₂–H₂O-doped ZnTPP and H₂TPP devices by analysis of the forward current–voltage characteristics.