Even if organic solar cells (OSCs) could have many advantages with respect to silicon devices, their industrial implementation is still limited by some relevant drawbacks. Besides reduced stability and efficiency, the commonly used techniques in laboratory are not suitable for application on industrial scale. To improve efficiency of the devices, morphology control during the active layer deposition results a key point for achieving high efficiency in OSCs. Optimized interpenetrating networks of donor and acceptor materials, nanoscale phase separation, and vertical percolation pathways are essential for effective separation, transport, and collection of the charges. Usually this control is obtained through the use of mixed organic solvents for the active layer deposition (chlorinated and/or aromatic solvents), the use of additives or post-fabrication treatments, as thermal or solvent annealing.1 The preparation of water-processable nanoparticle (NP) dispersions of semiconducting polymers recently emerged as an elegant technique to control morphology at nanoscale. At the same time, it allows lowering chlorinated solvents waste, thus reducing the environmental payback of energy obtained from OPVs and paving the way for the industrial application. The NPs dispersion can be obtained through the miniemulsion method that requires use of a great amount of surfactant agents to ensure NPs stability, the excess of surfactant has to be removed at the end of the process through dialysis.2 Rod-coil block copolymers (BCPs) can be powerful tools to achieve ideal morphologies because of their self-assembly capability that is strictly connected to the length of the two blocks and to their physical-chemical properties.3 We report on the PV application of rod-coil BCPs, PCPDTBT-b-P4VP, constituted by a low band-gap copolymer, PCPDTBT as the rigid segment, studied as donor material in hybrid and organic devices,4 and tailored segments of poly-4-vinylpyridine (P4VP) able to interact with acceptor materials commonly used in OPVs,5 as fullerene derivatives. Taking advantage of hydrophilic behavior of their flexible moiety, these amphiphilic rod-coil BCPs were used for preparing NPs in blend with PCBM, through miniemulsion method in aqueous medium without use of surfactants, thus avoiding dialysis purification. The NPs were fully morphologically and electrically characterized, showing suitable properties for PV application. The PCBM:BCP blend NPs dispersed in aqueous medium were used for the preparation of efficient eco-friendly OSCs, reaching a power conversion efficiency over 2%, near the best result reported for the same system studied in chlorinated solvents.6 1. Polymers 2014, 6, 2832 2. Nature Mat 2003, 2, 408 3. Mater Sci Eng R 2008, 62, 37 4. ACS Nano 2013, 7, 4846; Chem Commun 2013, 49, 8602 5. Eur Pol J 2014, 60, 222 6. Adv Mater 2010, 22, 367
TOWARDS ECO-FRIENDLY WATER-PROCESSABLE ORGANIC SOLAR CELLS VIA LOW BAND-GAP ROD-COIL BLOCK COPOLYMERS
STEFANIA ZAPPIA;GUIDO SCAVIA;UMBERTO GIOVANELLA;
2016
Abstract
Even if organic solar cells (OSCs) could have many advantages with respect to silicon devices, their industrial implementation is still limited by some relevant drawbacks. Besides reduced stability and efficiency, the commonly used techniques in laboratory are not suitable for application on industrial scale. To improve efficiency of the devices, morphology control during the active layer deposition results a key point for achieving high efficiency in OSCs. Optimized interpenetrating networks of donor and acceptor materials, nanoscale phase separation, and vertical percolation pathways are essential for effective separation, transport, and collection of the charges. Usually this control is obtained through the use of mixed organic solvents for the active layer deposition (chlorinated and/or aromatic solvents), the use of additives or post-fabrication treatments, as thermal or solvent annealing.1 The preparation of water-processable nanoparticle (NP) dispersions of semiconducting polymers recently emerged as an elegant technique to control morphology at nanoscale. At the same time, it allows lowering chlorinated solvents waste, thus reducing the environmental payback of energy obtained from OPVs and paving the way for the industrial application. The NPs dispersion can be obtained through the miniemulsion method that requires use of a great amount of surfactant agents to ensure NPs stability, the excess of surfactant has to be removed at the end of the process through dialysis.2 Rod-coil block copolymers (BCPs) can be powerful tools to achieve ideal morphologies because of their self-assembly capability that is strictly connected to the length of the two blocks and to their physical-chemical properties.3 We report on the PV application of rod-coil BCPs, PCPDTBT-b-P4VP, constituted by a low band-gap copolymer, PCPDTBT as the rigid segment, studied as donor material in hybrid and organic devices,4 and tailored segments of poly-4-vinylpyridine (P4VP) able to interact with acceptor materials commonly used in OPVs,5 as fullerene derivatives. Taking advantage of hydrophilic behavior of their flexible moiety, these amphiphilic rod-coil BCPs were used for preparing NPs in blend with PCBM, through miniemulsion method in aqueous medium without use of surfactants, thus avoiding dialysis purification. The NPs were fully morphologically and electrically characterized, showing suitable properties for PV application. The PCBM:BCP blend NPs dispersed in aqueous medium were used for the preparation of efficient eco-friendly OSCs, reaching a power conversion efficiency over 2%, near the best result reported for the same system studied in chlorinated solvents.6 1. Polymers 2014, 6, 2832 2. Nature Mat 2003, 2, 408 3. Mater Sci Eng R 2008, 62, 37 4. ACS Nano 2013, 7, 4846; Chem Commun 2013, 49, 8602 5. Eur Pol J 2014, 60, 222 6. Adv Mater 2010, 22, 367I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
