Electrode, nanostructure, interface and process engineering towards high performance flexible polymer solar cells

Abstract

Considerable attention has been devoted to polymer solar cells (PSCS) as potential next-generation solar energy-harvesting devices, owing to their low manufacturing cost and the possibility of fabricating PSCs in lightweight flexible plastic. In spite of the intensive research efforts in this field, the performance of PSCs is still far away from commercialization level requirements, primarily because the short exciton diffusion length of organic semiconductor limits the active layer thickness for efficient light absorption. Although polymer/fullerene bulk heterojunction (BHJ) system has been employed to increase the number of interfaces for facilitating charge separation, the low carrier mobilities and tortuous transport paths in these structure increase recombina-tion losses in thicker devices. Therefore, it is important to develop efficient light-trapping structures that can maximize light absorption, and at the same time ensure the resulting carrier can be efficiently collected by elec-trodes, with minimum recombination loss.In chapter 2, we optically and electrically designed and experimentally demonstrated a highly efficient top-illuminated flexible polymer solar cells on the nano-patterned polyethylene terephthalate (PET) substrates with 3D nano-patterned microresonant cavity. To enable optimum carrier transport in the dielec-tric/metal/dielectric (DMD) transparent electrode-based solar cells through a nanopatterned micro resonant cavi-ty, we precisely controlled the thickness of the photoactive and transporting layers. Then, the optical-field distri-bution inside the photoactive layer was tuned by the out-of-cell capping layer’s thickness and nanopattern. Fi-nally, the PET substrates under the PS mask was etched by reactive ion etching with a line-shaped pattern 50nm in height and 500nm in width. Then, each layer of device was conformally coated onto the nanpatterned PET substrates, confining the incident light within active layer. The resulting 3D nano...