Photovoltaic cell

DETAILED DESCRIPTION What is claimed is: 1.
A photovoltaic cell (10) comprising an electrolyte (14) which comprises a dissolved spiro or heterospiro hole conductor compound of the formula (I), ##STR38## wherein .
PSI.
is C, Si, Ge or Sn, and K.
sup.
1 and K.
sup.
2 are, independently of one another, conjugate systems, as redox system, and wherein the electrolyte (14) is in a liquid state.
2.
A cell as claimed in claim 1 wherein the spiro or heterospiro compound is a spirobifluorene derivative of the formula (II), ##STR39## where .
PSI.
is C, Si, Ge or Sn and the benzo groups may, independently of one another, be substituted and/or fused.
3.
A cell as claimed in claim 2 wherein the 9,9'-spirobifluorene derivative is a compound of the formula (III), ##STR40## where the symbols and indices have the following meanings: .
PSI.
is C, Si, Ge or Sn, K.
sup.
1, L, M, N.
sup.
1, R.
sup.
1, R.
sup.
2, R.
sup.
3, R.
sup.
4 are identical or different and are each a) hydrogen, NO.
sub.
2, --CN, --F or --Cl, b) a straight-chain or branched alkyl radical having from 1 to 20 carbon atoms, where b1) one or more nonadjacent CH.
sub.
2 groups can be replaced by , --O--, --S--, --CO--O--, --O--CO--, --O--CO--O--, NR.
sup.
5 or --Si(CH.
sub.
3).
sub.
2 -- and/or b2) one or more CH.
sub.
2 groups can be replaced by --CH.
dbd.
CH--, --C.
ident.
C--, 1,4-phenylene, 1,4-cyclohexylene or 1,3-cyclopentylene and/or b3) one or more H atoms can be replaced by F and/or Cl, and/or c) one of the following groups: ##STR41## ##STR42## X, Y.
sup.
1 are in each case identical or different and are .
dbd.
CR.
sup.
7 -- or .
dbd.
N--; Z is --O--, --S--, --NR.
sup.
5 --, --CRR--, --CR.
dbd.
CR-- or --CR.
dbd.
N--; R.
sup.
5, R.
sup.
6 are in each case identical or different and are each a) hydrogen b) a straight-chain or branched alkyl radical having from 1 to 20 carbon atoms, where b1) one or more nonadjacent CH.
sub.
2 groups which are not bound to nitrogen can be replaced by --O--, --S--, --CO--O--, --O--CO--, --O--CO--O-- or --Si(CH.
sub.
3).
sub.
2 -- and/or b2) one or more CH.
sub