The effect of nanopatterning and surface modification on the blend morphology of bulk-heterojunction (BHJ) organic photovoltaic cell(OPVC)

Abstract

Harnessing solar energy is one of the promising ways to solve today’s energy problems. Among the various solar cells system, intensive research has been conducted towards the development of organic photovoltaic due to its potential for the production of low-cost, easily processible, and flexible devices with acceptable efficiency. The energy conversion process in organic solar cells has four fundamental steps in the commonly accepted mechanism : 1) Absorption of light and generation of excitons, 2) diffusion of exciton, 3) charge separation and 4)charge transport and collection[1]. And the performance is the product of four efficiency of each step. So for enhancing the efficiency of organic solar cells, we need to increase the efficiency of each step. A significant breakthrough was achieved with the advent of bulk-heterojunction system based on π-conjugated polymer as electron donor and fullerene derivatives as electron acceptors. The key parameters for efficient BHJ solar cells are three dimensional morphology of blended films, including phase separation of blends, crystallinity and orientation of polymer chain, because of the diffusion of excitons, separation and collection of charges are greatly affected by these morphologies. The size of donor and acceptor domains should be in the range of exciton diffusion length (~10nm) for efficient separation, while maintaining the bicontinuous pathway to each electrode for charge transport and collection. And the charge transport in conjugation polymer is anisotropic due to delocalized electrons along the polymer backcones and the overlap of π-orbitals. Consequently, charge transport, mobility and collection can be significantly affected by blend morphology. In chapter 2, we investigate the blend morphology of nanopatterned P3HT:PCBM mixture films according to different process conditions of pattering procedures and its effect on the performance of organic photovoltaic cell (OPVC). The patterns were prepared by therma...