TECHNOLOGY FOCUS - POLYMERS - Preparation: No preparation method is given. Preferred Components: In the complex, at least one of the n ligands (L1) a(i.e. (L1) 1-(L1) n) comprises a pyridine ring or a ring system comprising a pyridine ring connected by a covalent bond or fused to the five-membered heteroring and/or to the six-membered ring comprising at least two heteroatoms, where the pyridine ring or a ring system comprises a pyridine ring (optionally substituted). The complex is overall neutral or carries an overall positive or negative charge. In the device, the complex and its reduced or oxidized counterpart is used as a redox-pair. In the device, any (L2) a(i.e. (L2) 1-(L2) n) is pyridine or polypyridine ligand, pyrazole, pyrazine, triazole, pyridazine, imidazole (all optionally substituted by 1-40C hydrocarbyl (optionally comprising 0-20 heteroatoms, halogens, nitro, amine or hydroxy)). The charge transport layer comprises an organic solvent, and/or at least one ionic liquid. The first electrode is a semiconductor electrode comprising a surface facing the charge transport layer of the device, where on the surface, there is adsorbed a dye so as to form a layer on the surface, and the dye is dyes carrying no charge or carrying a positive charge when being adsorbed on the surface. The dye (when adsorbed on the surface) lacks any negatively charged, free (non-anchored) anchoring group. The dye comprises a single anchoring group, where the dye is attached to the surface. Preferred Definitions:    (L1) a=63 heteroaryl compounds e.g. substituted pyridinyl compounds of formula (a1), substituted (2,2')bipyridinyl compounds of formula (a2), substituted (1,10)phenanthrolinyl compounds of formula (a3), substituted (1,7)phenanthrolinyl compounds of formula (a4), substituted (4,7)phenanthrolinyl compounds of formula (a5), substituted (1,2,4)triazinyl compounds of formula (a6), substituted (1,2,3,5)tetrazinyl compounds of formula (a7), substituted pyrrol-1-ide compounds of formula (a8), and substituted 1H-pyrrolyl compounds of formula (a9) or (a10), where, if (L1) ais of formulae (a1)-(a5), then at least one substituents R 1-R 8is 76 heteroaryl compounds e.g. substituted 2H-pyrrol-2-yl compounds of formula (b1), substituted 2H-pyrrol-3-yl compounds of formula (b2), substituted 2H-pyrrol-1-yl compounds of formula (b3), substituted 2H-pyrrol-2-yl compounds of formula (b4) or (b5), substituted 4H-pyrazol-4-yl compounds of formula (b6), substituted 2H-imidazol-2-yl compounds of formula (b7), substituted 4H-(1,2,3)triazol-4-yl compounds of formula (b8), substituted 1H-(1,2,3)triazol-4-yl compounds of formula (b9), substituted 1H-tetrazol-5-yl compounds of formula (b10), substituted isoindol-2-yl compounds of formula (b11), substituted 1H-indazol-2-yl compounds of formula (b12), and substituted benzotriazol-2-yl compounds of formula (b13);    R 1-R 8=1-50C hydrocarbyl (optionally containing 0-20 heteroatoms), H, halo, -NO 2, NH 2or -OH;    R1m, R2m=(-CH 2R 1), (-CHR 1R 2) or (-CR 1R 2R 3);    (L2) a=32 heteroaryl compounds e.g. substituted pyridinyl compounds of formula (k1), substituted (2,2')bipyridinyl compounds of formula (k2), substituted (1,10)phenanthrolinyl compounds of formula (k3), substituted pyrrol-1-ide compounds of formula (k4), substituted 1H-pyrrole compounds of formula (k5), substituted 1H-imidazol-3-ium compounds of formula (k6), and substituted (2,2';6',2'')terpyridine compounds of formula (k7);    one of R1a-R8a, and R1b-R6b=1-30C hydrocarbyl (optionally comprising 0-20 heteroatoms), halo, -NO 2, -NH 2or -OH or H, where R1a-R8a, and R1b-R6b are substituted by 61 heteroaryl compounds e.g. substituted pyrrol-1-yl compounds of formula (d1), substituted 1H-pyrrol-2-yl compounds of formula (d2), substituted isoindol-2-yl compounds of formula (d3), substituted 1H-indazol-2-yl compounds of formula (d4), and substituted benzotriazol-2-yl compounds of formula (d5);    R1s, R2s=CR1fR2fR3f; and    R1f-R3f=1-30C hydrocarbyl (optionally comprising 0-20 heteroatoms or halo) or H, where R1f is -NO 2, -NH 2or -OH, if R2f and R2f are not halo, -NO 2, -NH 2or -OH.    EXAMPLE - Cobalt chloride hexahydrate (91 mg) was dissolved in water (25 ml) and in another flask, pyridine-pyridine-pyrazole ligand (93 mg) was dissolved in acetone (25 ml). The two solutions were combined and heated to 55 degrees C for 2 hours. Then, ammonium hexafluorophosphate (400 mg) dissolved in water (100 ml) was added to the reaction mixture. The reaction mixture was stored overnight at 3 degrees C for precipitation. Then the product was collected on a sintered glass frit and dried in vacuum, to obtain bis(6-pyrazol-1-yl-(2,2')bipyridinyl)cobalt(II) dihexafluorophosphate complex (yield 95 mg).