Environmental Passivation and Temperature Cycling of PCBM - Polymer Solar Cells
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1031-H09-23
Environmental Passivation and Temperature Cycling of PCBM - Polymer Solar Cells Annick Anctil1,2, Andrew Merrill2, Cory Cress1,2, Brian Landi2, and Ryne Raffaelle1,2 1 Microsystems Engineering, Rochester Institute of Technology, Rochester, NY, 14623 2 Nanopower Research Laboratories, Rochester Institute of Technology, 85 Lomb Memorial Drive, Rochester, NY, 14623 ABSTRACT In the present work, polymer solar cells were fabricated from composite blends of poly[2methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) and poly(3-hexylthiophene)(P3HT with PCBM[60] and PCBM[70]. The composite blends were used as active layers in an ITO/PEDOT:PSS/active layer/Al device structure. Power conversion efficiencies have been measured from current-voltage (I-V) measurements for each of these different composite blends under simulated AM1.5 illumination. In the case of the MEH-PPV devices, the I-V performance has been measured as a function of polymer molecular weight, type of fullerene derivative (C60 or C70), and PCBM:polymer ratios. The highest efficiencies for the ranges used in this study were obtained using the 150,000 g/mol MEH-PPV molecular weight, the C70 PCBM derivative, and a 1:4 MEH-PPV:PCBM ratio. The effect of thermal cycling on the I-V performance for both MEH-PPV and P3HT devices has also been measured from 77K to 330K. The devices exhibited a positive temperature coefficient for the short-circuit current density (Jsc), which dominated the overall efficiency of the device over this temperature range. Finally, the use of a combination of parylene and polymethylmethacralate for device passivation was shown to provide a dramatic reduction in device degradation under ambient conditions as compared to non-passivated devices. INTRODUCTION Recent progress with P3HT devices has resulted in efficiencies of approximately 5%[1], although concerns over limitations due to material properties (i.e. bandgap, mobility, etc.) promote alternative strategies. The use of MEH-PPV as an active layer has shown promise, although with limited efficiencies to date [2]. In devices incorporating P3HT, it has been shown that higher molecular weight (MW) P3HT resulted in slower degradation and increased glass transition temperature (Tg) [3]. This result will obviously affect the usable temperature range of these devices. Faster degradation is expected to occur at a temperature close to the Tg due to the increased motion of the polymer chains and possible diffusion of electrode degradation products [4]. Comparable studies of MEH-PPV blends are presently lacking, but may offer advantages in terms of environmental stability and power conversion efficiency. Conventional polymer devices generally employ a PEDOT:PSS layer and a derivatized polythiophene or polyphenylenevinylene (PPV) composite blend sandwiched between two electrodes. It is well established that exposure to ambient atmosphere will degrade device performance on the order of hours to a few days. Practical implementation of these devices will rely upon the development of
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