All-polymer solar cells (APSC) are a class of organic solar cells in which hole and electron transporting phases are made of conjugated polymers. Unlike polymer/fullerene solar cell, photoactive material of APSC can be designed to have hole and electron transporting polymers with complementary absorption range and proper frontier energy level offset. However, the highest reported PCE of APSC is 5 times less than that of polymer/fullerene solar cell. The low PCE of APSC is mainly due to: i) low charge separation efficiency; and ii) lack of optimal morphology to facilitate charge transfer and transport; and iii) lack of control over the exciton and charge transport in each phase. My research work is focused towards addressing these issues. The charge separation efficiency of APSC can be enhanced by designing novel electron transporting polymers with: i) broad absorption range; ii) high electron mobility; and iii) high dielectric constant. In addition to with the above parameters chemical and electronic structure of the repeating unit of conjugated polymer also plays a role in charge separation efficiency. So far only three classes of electron transporting polymers, CN substituted PPV, 2,1,3-benzothiadiazole derived polymers and rylene diimide derived polymers, are used in APSC. Thus to enhance the charge separation efficiency new classes of electron transporting polymers with the above characteristics need to be synthesized. I have developed a new straightforward synthetic strategy to rapidly generate new classes of electron transporting polymers with different chemical and electronic structure, broad absorption range, and high electron mobility from readily available electron deficient monomers. In APSCs due to low entropy of mixing, polymers tend to micro-phase segregate rather than forming the more useful nano-phase segregation. Optimizing the polymer blend morphology to obtain nano-phase segregation is specific to the system under study, time consuming, and not trivial. Thus to avoid micro-phase segregation, nanoparticles of hole and electron transporters are synthesized and blended. But the PCE of nanoparticle blends are far less than those of polymer blends. This is mainly due to the: i) lack of optimal assembly of nanoparticles to facilitate charge transfer and transport processes; and ii) lack of control over the exciton and charge transport properties within the nanoparticles. Polymer packing within the nanoparticle controls the optoelectronic and charge transport properties of the nanoparticle. In this work I have shown that the solvent used to synthesize nanoparticles plays a crucial role in determining the assembly of polymer chains inside the nanoparticle there by affecting its exciton and charge transport processes. To obtain the optimal morphology for better charge transfer and transport, we have also synthesized nanoparticles of different radius with surfactants of opposite charge. We propose that depending on the radius and/or Coulombic interactions these nanoparticles can be assembled into mineral structure-types that are useful for photovoltaic devices.

Les cellules solaires organiques (OSC) apparaissent comme une technologie prometteuse pour les énergies renouvelables en raison de leur poids léger, leur grande flexibilité et leur processus de fabrication peu coûteux. Jusqu'à présent, la plupart des OPV ont utilisé des dérivés de Fullerene, tels que PCBM ou PC71BM, en tant qu'accepteur d'électrons dans la couche active, qui s'est avéré être un goulet d'étranglement pour cette technologie. Par conséquent, le développement d'accepteurs non-fullerene est devenu la nouvelle force motrice de ce domaine. Les cellules solaires tout-polymères (tous-PSC) qui ont les avantages de la robustesse, de la stabilité et de l'accessibilité ont déjà atteint PCE jusqu'à 9%. Ainsi, le développement de nouveaux matériaux accepteurs est impératif pour améliorer les performances de tous les PSC. / Organic solar cells (OSCs) appear as a promising technology for renewable energy owing to their light weight, great flexibility and low-cost fabrication process. So far most of the OPV shave been using fullerene derivatives, such as PCBM or PC71BM, as the electron acceptor in the active layer, which have been proven to a bottleneck for this technology. Therefore,developing non-fullerene acceptors has become the new driving force for this field. All-polymer solar cells (all-PSCs) that have the advantages of robustness, stability and tunability have already achieved PCE up to 9%. Thus, developing novel acceptor materials is imperative for improving the performance of all-PSCs.