NOVELTY - An inverted tandem polymer photovoltaic device has a hole-extracting electrode, an electron extracting electrode spaced apart from the hole-extracting electrode, a first bulk hetero-junction polymer semiconductor layer, a second bulk hetero-junction polymer semiconductor layer spaced apart from the first bulk hetero-junction polymer semiconductor layer, a p-type layer provided between the first and second bulk hetero-junction polymer semiconductor layers, and an n-type layer.    USE - Inverted tandem polymer photovoltaic device i.e. tandem electronic or electro-optic device such as a polymer solar cell device or photodetector device (all claimed).    ADVANTAGE - The device has better photovoltaic effect, high mobility, flexibility and easy processibility. The device is inexpensive and light in weight.    DETAILED DESCRIPTION - An inverted tandem polymer photovoltaic device has a hole-extracting electrode, an electron extracting electrode spaced apart from the hole-extracting electrode, a first bulk hetero-junction polymer semiconductor layer, a second bulk hetero-junction polymer semiconductor layer spaced apart from the first bulk hetero-junction polymer semiconductor layer, a p-type layer provided between the first and second bulk hetero-junction polymer semiconductor layers, and an n-type layer, where the p-type layer is in physical contact with one of the first and second bulk hetero-junction polymer semiconductor layers, the n-type layer is in physical contact with the other of the first and second bulk hetero-junction polymer semiconductor layer, and the p-type and the n-type layers are doped to an extent that charge carriers tunnel through the p-type and/or n-type layer. An INDEPENDENT CLAIM is also included for an electronic or electro-optic device comprising a first electrode, a second electrode spaced apart from the first electrode, and a layer of active material disposed between the first electrode and the second electrode, where the active layer comprises a polymer comprising substituted 1,5-dihydro-s-indacene compound of formula (I).    R1-R3=18C alkyl or optionally substituted aryl;    X=O, S, Se or N;and    Ar1,Ar2=1-5 monocyclic arylene, bicyclic arylene, polycyclic arylene, monocyclic heteroarylene, bicyclic heteroarylene or polycyclic heteroarylene (all optionally fused or linked).    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of a tandem electro-optic device.    Tandem electro-optic device (100)    Electrodes (102, 104)    Active layer (106)    Material layer (108)