TECHNOLOGY FOCUS - INSTRUMENTATION AND TESTING - Preferred Components: The organic layer comprises a hole transport layer, a hole injection layer, an electron injecting layer, and an electron transport layer. The photoactive layer comprises an electron donor and an electron acceptor, where the electron donor comprises the copolymer. The photoactive layer has a bilayer structure, and further comprises an n-type organic compound layer and a p-type organic compound layer. The p-type organic compound layer comprises the copolymer.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Components: The electron acceptor is fullerene, fullerene derivatives, carbon nanotube, carbon nanotube derivatives, and/or basocuproin based semiconductive element.    TECHNOLOGY FOCUS - POLYMERS - Preferred Components: The copolymer is of formula (-((B1a-C1)l-(B2a-A)m)n-). The unit B acts as an electron donor. The unit B has divalent groups of formulae (A)-(J). The copolymer further comprises: a unit C comprising optionally substituted heterocyclic ring containing one or more of N, O or S atoms and having optionally substituted aryl. The unit C acts as an electron acceptor. The unit C has divalent groups of formulae (i)-(viii). The unit A is present in an amount of 0.01-30 mole%. The unit B is present in an amount of 50-80 mole%. The unit C is present in an amount of 0-30 mole%. The copolymer has number average molecular weight of 500-1000000 g/mole and molecular weight distribution of 1-100.a, b = 1-3;c = 1-6;X1-X3 = C(Ra1)(Rb1), N(Ra1), O, Si(Ra1)(Rb1), P(Ra1), S, Ge(Ra1)(Rb1), Se or Te;Y1, Y2 = C(Ra1), N, Si(Ra1), P or Ge(Ra1);R10-R13, Ra1, Rb1 = alkyl, cycloalkyl, alkoxy, aryl, alkylamine, arylamine, alkyl sulfoxide, aryl sulfoxide, alkenyl, silyl, B, alkylamine, aralkyl, amine, fluorenyl, carbazole, heterocyclic group comprising N, O or S (all optionally substituted), H, D, halo, nitrile group, nitro, imide, amide or OH;d = 1-2;e = 1-3;R14-R17 = R10-R13;X5-X8 = X1-X3;Y3-Y5 = Y1, Y2;l, m = 0-1;l+m = 1;n = 1-10000;B1a, B2a = unit B;C1 = unit C; andA = unit A. EXAMPLE - No suitable example given.