TECHNOLOGY FOCUS - ELECTRONICS - Preferred Components: The heterojunction device further comprises one or more electron donors or electron acceptors.    TECHNOLOGY FOCUS - POLYMERS - Preferred Composition: In (I), at least one of the blocks is conjugated. (I) is: fully conjugated; diblock copolymer; and free of amphiphilic substituents. (I) is a triblock copolymer having a structure of ADA, DAD, ADA' or DAD', where A and A' represent different electron acceptor blocks and D and D' are different electron donor blocks. (I) comprises a first block of controlled polydispersity and other block is formed via a chain extension process performed on the first block. (I) comprises a first block of controlled polydispersity and other block comprising a preformed macromonomeric unit linked to the first block. (I) comprises the monomers, which is triarylamine, 9,9-dioctylfluorene and benzothiadiazole. Preferred Components: The polydispersity of the block is less than or equal to 2, preferably less than or equal to 1.5. The chain length of the blocks is such that the number average molar mass is 4000-100000 Daltons. The first block is a central block and the other block is an end block. The copolymer assembles in the solid phase in length scales of less than or equal to 100 nm, preferably 15-40 nm. The polydispersity of the central block is controlled through polymerization. The blocks are based on repeat units comprising linear, branched, fused or linked aromatic, heteroaromatic, arylene vinylene and heteroarylene vinylene. The repeat units comprise a sulfur condensed heterocycle. In (I), the energy level of the highest occupied molecular orbital (HOMO) for the electron donor block is -6.5 to -4.5 eV. The energy level of the HOMO for the electron acceptor block is below that of the energy level of HOMO of the electron donor block and the energy level of the lowest unoccupied molecular orbital for the electron acceptor block is at least 1 eV higher than the energy level of the HOMO of the electron donor block. Preferred Process: The polymerization technique comprises controlled living or quasi living polymerization, quasi living Suzuki polycondensation or living free radical polymerization. The polydispersity is controlled through physical separation, where the physical separation is achieved by solubility difference or chromatography. EXAMPLE - A reaction mixture containing Block D copolymer of formula (A1) (0.504 g), Block C copolymer of formula (B1) (1.075 g), and tetraethylammonium hydroxide (20 wt.% in water) was degassed by bubbling a stream of nitrogen through it for 30 minutes. The catalyst, tetrakis(triphenylphosphine) palladium (5 mg, excess), was added and the nitrogen stream continued for 10 minutes before the reaction mixture was stirred at 80?0C for 16 hours. The reaction mixture was filtered through silica, the volume of the filtrate was reduced to 5 ml and the product was precipitated by dropwise addition of the toluene solution to a rapidly stirred methanol (100 ml) and worked up to give triblock copolymer of formula (C1) (90 %).