Towards large scale organic photovoltaics

Large area organic photovoltaic (OPV) modules are gaining a lot of interest due to their potential for low cost electricity generation. Modules are typically fabricated from organic polymeric solutions using reel-to-reel (R2R) techniques such as slot-die coating. Control of the nanoscale morphology of the polymeric solutions during deposition has so far proven difficult. Here, we present a novel method for fabricating the active layer of OPV modules using colloidal suspensions of polymer nanoparticles. The nanoscale morphology of the active layer can be directly controlled using the nanoparticulate approach. We have shown that through careful control of the surface energy of the films produced, multiple layer films can be constructed. Multiple layer films are important because previous work in the literature using single layer nanoparticle films has shown very poor device performance. Multilayer nanoparticulate devices were constructed using nanoparticles containing blends of PFB:F8BT. The devices were constructed with both aluminium and calcium/aluminium electrodes and showed a large improvement in efficiency as compared to previous work. Interestingly these nanoparticulate devices were twice as efficient as the highest known bulk heterojunction devices. As OPV cells increase in size series resistance can limit module performance. The origin of the series resistance in OPV cells is probed and the area dependent resistances are identified. The contribution to the series resistance from the aluminium cathode is shown to be significant in some cases and can detrimentally affect device performance. A novel coating technique for the formation of the films used in OPV modules is described. The relationship between coating velocity and film thickness is shown to control the coating process. Proof-of-concept OPV modules have been produced, showing great promise for the efficient production of large area OPV modules. This work illuminates a pathway for constructing highly efficient, large area modules from aqueous dispersions that promise to fulfil the potential of organic photovoltiacs.