Perspectives of organic photovoltaic devices as next generation solar cells for sustainable energy

Abstract

Organic solar cells, especially polymer based devices, frequently called polymer solar cells, are recently gaining popularity due to the simple process and the relatively low cost compared with silicon-based solar cells. The structure of the organic solar cells is composed of a photoactive layer and two electrodes that are different work functions. The anode electrode is a semitransparent oxide layer, its role is to allow light to pass through and to transfer electron back to the cells. It coats on top of a transparent substrate, usually glass. The cathode electrode is a layer of thin metal. The perspectives focusing on recent progress of organic photovoltaics in terms of efficiency, durability, energy payback time, and CO2 emission rate was reviewed in this contribution. Organic photovoltaics are lightweight and flexible as compared to those of the conventional silicon and other inorganic semiconductors-based cells. Efforts now focus on their efficiency and lifetime. Recent progress of the power conversion efficiency of organic photovoltaics has been reached up to 10-11 %. While the lifetime of a polymer-based solar cell lasted 7 years. Such progress is based on the developments of various kinds of organic and inorganic semiconducting materials, transparent conducting metal oxide coated substrates, metal electrodes, sealing films, and the assembling of the new materials to construct the highly efficient polymer solar cells. In particular, new materials of p- and n-type organic semiconductors of polymers and fullerenes as active layer and nanostructured metal oxides as interlayer effectively enhanced open circuit voltage and improved the electron conduction to the anode through the formation of highly efficient carrier path, which brings large short circuit current density. Construction of tandem solar cell is another promising strategy to achieve high power conversion efficiency. Through the numerical calculations, 14-20% is predictable by taking the tandem structure. It was also estimated that organic photovoltaic system would become one of the future power generation systems showing relatively short energy payback time of 1.35 year and low CO2 emission rate of 37.8 g-CO2/kWh, when the power conversion efficiency was 3% as compared with those of the conventional silicon and other inorganic semiconductors-based cells.