Factors Limiting Device Efficiency in Organic Photovoltaics

• Published in: Advanced materials (Weinheim) 2013-04, Vol.25 (13), p.1847-1858
• Main Authors: Janssen, René A. J., Nelson, Jenny
• Format: Article
• Language: English
• Subjects: Computational efficiency; Computing time; Constraining; Devices; Empirical analysis; Mathematical models; organic electronics; Photovoltaic cells; photovoltaic devices; polymeric materials; semiconductors; Solar cells
• ISSN: 0935-9648; 1521-4095
• DOI: 10.1002/adma.201202873

The power conversion efficiency of the most efficient organic photovoltaic (OPV) cells has recently increased to over 10%. To enable further increases, the factors limiting the device efficiency in OPV must be identified. In this review, the operational mechanism of OPV cells is explained and the detailed balance limit to photovoltaic energy conversion, as developed by Shockley and Queisser, is outlined. The various approaches that have been developed to estimate the maximum practically achievable efficiency in OPV are then discussed, based on empirical knowledge of organic semiconductor materials. Subsequently, approaches made to adapt the detailed balance theory to incorporate some of the fundamentally different processes in organic solar cells that originate from using a combination of two complementary, donor and acceptor, organic semiconductors using thermodynamic and kinetic approaches are described. The more empirical formulations to the efficiency limits provide estimates of 10–12%, but the more fundamental descriptions suggest limits of 20–24% to be reachable in single junctions, similar to the highest efficiencies obtained for crystalline silicon p‐n junction solar cells. Closing this gap sets the stage for future materials research and development of OPV. The power conversion efficiency of donor‐acceptor organic solar cells now reaches over 10% in single‐junction and tandem cells. Empirical models suggest that the maximum efficiency may be limited at 10–12%, yet recent, more refined detailed‐balance models indicate that, under favorable conditions, efficiencies in the range of 20–24% can be achieved.