Optical Optimization of Tandem Structure Formed by Organic Photovoltaic Cells Based on P3HT: PCBM and PBBTDPP2: PCBM Interpenetrating Blends

Abstract

AbstractThe chapter focuses on the optical optimization of the tandem structure composed of organic photovoltaic (OPV) cells based on interpenetrating blend materials P3HT: PCBM and pBBTDPP2: PCBM. For this purpose, a simulation based on the transfer matrix formalism is developed. The aim is to calculate the current (JSC) (assuming 100% internal Quantum efficiency). Optical performance of the two OPV cells separately is studied. Firstly, the P3HT: PCBM OPV cell is optimized to find the geometry of the stack giving the best optical properties. The OPV cell structure is given by: glass/ITO/PEDOT: PSS/P3HT: PCBM/Ca/Al. The best JSC current value (in this case 12.48 mA/cm2) is reached for an active layer thickness dActive layer = 91 nm. In a second time, the optical yield of the OPV cell based on pBBTDPP2: PCBM interpenetrating blend is optimized. A comparison of the optical performance of this cell with those of OPV cells based on materials commonly used in the field of OPVs is carry out. The simulation shows a pBBTDPP2: PCBM interpenetrating blend OPV cell offering the best result (JSC = 17 mA/cm2) in addition of a high absorption in the 600–800 nm range. Finally, the tandem structure formed by the two OPV cells is studied taking into account the arrangement of the two cells with respect to each other. Two configurations are considered namely, the Normal Tandem Solar Cell (NTSC) which considers P3HT: PCBM blend layer as the front active layer and pBBTDPP2: PCBM blend layer as the back active layer and the Reverse Tandem Solar Cell (RTSC) which considers pBBTDPP2: PCBM blend layer on top of the tandem structure and P3HT: PCBM blend layer on the back of the device. The aim is to find for both configurations the optimized thicknesses of the blend active layers of the front and rear OPV cells giving the highest current matching. Results show that NTSC configuration is more efficient for the large thicknesses of the top cell, whereas the RTSC configuration is more efficient for the thin thicknesses of the top cell.KeywordsOptical modelingOrganic solar cellP3HT: PCBM blendpBBTDPP2: PCBM blendTandem structureCurrent matching