Amphiphilic low band-gap rod-coil block copolymers: synthesis, characterization and hybrid PV application

Rod-coil block copolymers (BCPs) can be powerful tools to achieve ideal morphologies in bulk heterojunction (BHJ) solar cells, which require an interprenetrating network between donor and acceptor material at the nanoscale. Their self-assembly behavior is strictly connected to the lenght of the two blocks and to the synthetic route to their preparation. Step-growth strategy implies the preparation of two blocks properly functionalized to covalently react. Chain-growth method consists, instead, of the preparation of a macroinitiator activated with an end-group directly capable to promote the polymerization of the second block or to be converted into a functional group able to do it. Many conjugated polymers were used as rigid moiety in BCPs for solar cells. For the fist time, we used a low band-gap copolymer, poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b:3.4-b']dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (PCPDTBT) intesively studied as donor material into hybrid solar cells (HSCs). Poly-4-vynilpyridine (P4VP), was selected as flexible segment that allows the interaction with acceptor materials, in particular semiconducting inorganic nanoparticles, as CdSe nanocristals (NCs). Exploiting both synthetic approaches, with a proper combination of Suzuki Coupling and Nitroxide-Mediated Radical Polymerization (NMRP), two different series of BCPs were obtained, deeply investigated to elucidate their molecular structure, and then tested into the active layer of HSCs, as nanostructuring compatibilizer.