Textured substrate based organic solar cell for higher absorption and improved performance
- PDF / 590,613 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 42 Downloads / 190 Views
1210-Q03-29
Textured substrate based organic solar cell for higher absorption and improved performance Kanwar S. Nalwa1,3, Joong-Mok Park2, Wai Leung3, Kristen Constant4, Kai-Ming Ho2 and Sumit Chaudhary1,3,4 1 Department of Electrical and Computer Engineering, Iowa state University, Ames, IA-50011 (USA) 2 Ames Laboratory-USDOE & Department of Physics and Astronomy’ Iowa State University, Ames, IA 50011 (USA) 3 Microelectronics Research Center, Iowa State University, Ames, IA 50011 (USA) 4 Department of Materials Science and Engineering, Iowa State University, Ames, IA 50011 (USA)
ABSTRACT The performance of polymer-based photovoltaic devices is limited by several factors like high band-gap and low charge-carrier mobility, to name a few. Thicker active-layers have high optical absorption but the transport of carriers in them is inefficient. Thus the optimal thickness of the active-layers has to be determined carefully. This conflict can be resolved using a threedimensional (3D) microscale textured grating shaped solar cell geometry. The solar cells in this study were fabricated on photoresist gratings to give them 3D texture required for enhanced light absorption. Introduction of texturing has a significant effect on over all power conversion efficiency of the devices. Grating based solar cell having 2 micron pitch showed improved power conversion efficiency over the flat solar cell. In addition to favorable guiding of optical modes, the improvement in efficiency is accomplished by homogenous coverage of the spin-coated active layer, which is a challenging process for non-flat surfaces. Uniform thickness in this study was facilitated by the sufficiently high pitch and low height of the underlying photoresist gratings. INTRODUCTION Conjugated polymers have emerged as promising materials for photovoltaics primarily because of the prospect of high throughput solution-processible manufacturing using roll-to-roll or spray deposition. Most of the developments that have improved performance of Polymer based photovoltaic devices (PPVDs) are based on electron donor-acceptor heterojunctions. In a planar heterojunction, or ‘bilayer’ device, the donor-acceptor interface separates excitons which are created within diffusion length into charge carriers and contribute to the photovoltaic conversion process. This poses a serious limit to the thickness of the photovoltaic layer and hence the efficiency due to low absorption [1-3]. A revolutionary development in organic photovoltaics came in the mid-1990s with the introduction of a dispersed/bulk heterojunction, where an electron accepting and an electron donating material are blended together [4-6]. If the length scale of the blend is similar to the exciton diffusion length, then wherever an exciton is photogenerated in either material, it is likely to diffuse to an interface and break up. The
dissociation of excitons leads to free electrons and holes which may travel to the contacts, if continuous pathways exist in each material from the interface to the respective electrodes.
Data Loading...
