Low Cost Fabrication of High Efficiency Polymer Solar Cells

Cost effective and highly efficient renewable energy is playing a critical role in this present age with high demand for energy with zero emissions. The developments in organic solar cells (OSC) have the advantages of low cost and relatively simple construction in addition to compatibility with flexible polymer substrates. The type of OSC of primary focus in this paper is the polymer solar cell (PSC).  Due to their low-cost production and excellent electronic and photonic properties, polymers are very well suited for low-cost electronics and photovoltaics technology. Over the past years, the power conversion efficiencies of PSCs have steadily improved to reaching about 10%. The improvement in this study was possible because of changes made to the device structure, the optimization of processing parameters and the device processing techniques.

Polymer solar cells are third generation solar cells which emerged about a decade ago. Since then one of the goals has been to improve the PSCs by making it less expensive both in terms of cost and method of fabrication. The PSCs have been faced with the challenges of low efficiencies, low stability and low durability. The PSC basically use the solution-processed materials such as nanoparticles and polymers as opposed to expensive semiconductors, which makes it easier to manufacture using cheap and inexpensive method. Several methods are employed for the fabrication of these solar cells, which include, but are not limited to spin-coating, electrophoresis, knife over edge (doctor blading), screen printing, slot-die, coating, gravure printing and spray coating [1-3]. For the purpose of this research, the current method used is the spin-coating and the ink-jet printing, screen printing, and the doctor blading methods are anticipated method which will be used as the fabrication progress.

               I.         EXPERIMENTAL METHOD

A glass transparent slide was used as the substrate on which the active layer for the PSC is prepared. The active layer contains a mixture of poly(3-hexylthiohene0-2,5-diyl) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) dissolved in a specific volume of chlorobenzene which is then mixed and thoroughly stirred. The typical profile of a PSC is shown in Figure 1

The indium tin-oxide (ITO) layer is basically a polyethylene terephthalate (PET) with ITO coating. The ITO layer stands as the anode as is seen in Figure 1. The PEDOT: PSS: poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) layer is an electron blocking layer  which could act as anode in some designs. The PEDOT:PSS layer was spin-coated on the ITO. Our experimental work is aimed at eliminating defects such as irregularities and pinholes. Some earlier studies have shown that the annealing effect and also the effect of using various solvents for spray coating of P3HT:PCBM on PEDOT:PSS could help improve the physical, optical and electronic characteristics of the film [4,5]. The result of spray coating which is more efficient than the spin-coating of PEDOT:PSS and P3HT:PCBM films on ITO – coated glass substrate is shown in the 

The goal of this paper is to compare the different printing, coating and deposition techniques for the active layer and the PEDOT:PSS on the ITO and be able to determine the process which gives the highest efficiency and best characteristics. These various techniques and methods will be used to evaluate the performance of the material with the methods used, then characterization and analysis of the PSC material to determine if the resulting material would be of higher performance as whole.

             II.         REFERENCES

 [1] Krebs, F.C. Fabrication and processing of polymer solar cells: A review of printing and coating techniques. Sol. Energy Mater. Sol. Cells 2009, 93, 394–412.

[2] Søndergaard, R.R.; Hosel, M.; Krebs, F.C. Roll-to-roll fabrication of large area functional organic materials. J. Polym. Sci. Part B Polym. Phys. 2013, 51, 16–34.

[3] Wengeler, L.; Schmitt, M.; Peters, K.; Scharfer, P.; Schabel, W. Comparison of large scale coating techniques for organic and hybrid films in polymer based solar cells. Chem. Eng. Process. 2013, 68,38–44.

[4] Lee, J-H.; Sagawa, T.; Yoshikawa, S. Morphological and topographical characterizations in spray coated organic solar cells using an additional solvent spray deposition. Org. Electron. 2011, 12, 2165–2173.

[5] Lee, J-H.; Sagawa, T.; Yoshikawa, S. Thickness dependence of photovoltaic performance of additional spray coated solar cells. Thin Solid Films 2013, 529, 464–469.