Enhanced quantum yield in porphyrin/electron-donor double-layer solar cells

When the layer of 3-carboxymethyl-5-[(3-ethyl-2(3H)-benzothiazolylidine)ethylidene (MC(COOH)) is inserted into the Au/Zntpyp interface in Al/Zntpyp/Au sandwich-type solar cell (Zntpyp: 5,10,15,20-tetra(3-pyridyl)porphyrinatozinc), the photovoltaic properties are remarkably improved. For the Al/Zntpyp(thickness 10 nm)/MC(COOH)(20 nm)/Au cell, a short-circuit photocurrent (J(sc)) of 0.93 mu Acm(-2), open-circuit photovoltage (V-oc) of 0.71 V, fill factor (ff) of 0.41, and energy conversion yield (eta) of 3.6% are obtained when illuminated at the Al/Zntpyp interface with 455 nm monochromatic light of 7.5 mu Wcm(-2) intensity. A rapid electron-transfer from the donor MC(COOH) to photogenerated holes in Zntpyp suppresses the charge recombination of the photogenerated carriers. The energetically well-arranged valence band levels eventually enhance the eta value about 9 times compared with the Al/Zntpyp/Au cell. Further the Al/HD(9 nm)/MC(COOH)(20 nm)/Au cell using a longer-lived sensitizer (HD) instead of Zntpyp gives a J(sc) value of 2.36 mu Acm(-2), V-oc value of 0.69 V, ff value of 0.34, and eta value of 4.8% when illuminated with 445 nn monochromatic light of 11.7 mu Wcm(-2) intensity at the Al/HD interface, where HD represents a heterodimer consisting of 5,10,15-tri(4-chlorophenyl)-20-(3-pyridyl)porphyrin(H(2)pyp(3)p(Cl)) and 5,10,15,20-tetra(2,5-dimethoxyphenyl)porphyrinatozinc(Zntpp(OMe)(2)).