Characterization of polymer bulk heterojunction photocell with unmodified C70 prepared with halogen-free solvent for indoor light harvesting |
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| Affiliation: | 1. CAS Key Laboratory of Biomedical Diagnostics, Suzhou Institute of Biomedical Engineering and Technology, Chinese Academy of Science (CAS), 88 Keling Road, Suzhou 215163, China;2. Institute of Theoretical Chemistry, Jilin University, Changchun 130023, China;3. Department of Chemical and Biomolecular Engineering, Lafayette College, Easton 18042, PA, USA;1. Institute of Photoelectronic Thin Film Devices and Technology, Tianjin Key Laboratory of Photoelectronic Thin Film Devices and Technology, Nankai University, Tianjin 300071, PR China;2. Department of Mechanical Sciences and Engineering, Tokyo Institute of Technology, Meguro, Tokyo 152-8550, Japan;1. Instituto de Ciencia Molecular (ICMOL), Universidad de Valencia, Calle Catedrático José Beltrán, 2, 46980 Paterna, Spain;2. Skolkovo Institute of Science and Technology, 143025 Skolkovo, Moscow Region, Russia;3. Canatu Oy, Konalankuja 5, FI-00390, Helsinki Finland;4. Department of Applied Physics, Aalto University, School of Science, P.O. Box 15100, FI-00076 Aalto, Finland;5. St. Petersburg Polytechnic University, 195251, St. Petersburg, Russia |
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| Abstract: | Although photocells are commonly characterized under AM1.5G 100 mW cm−2 (1 sun) illumination, their performance under low light illumination is also important, because photocells are frequently used for indoor applications. In this study, polymer photocells based on a bulk heterojunction composite consisting of a low energy gap polymer PTB7 and unmodified C70 prepared with a halogen-free solvent 1,2,4-trimethylbenzene have been characterized under the illumination of 1 sun or below. A typical photocell with the power conversion efficiency (PCE) of 4% at 1 sun shows the PCE of approximately 7% at 10−3 sun, which seems to fit for some indoor applications such as a permanent power source for a wireless sensor node. The sublinear dependence of short-circuit photocurrent on light intensity as well as the increase of fill-factor under low light illumination yields the increased efficiency under low light illumination. An analysis employing a one-diode equivalent circuit model suggests that the increased parallel resistance as well as the decreased saturation current of the diode under low light illumination accounts for the latter feature. It is also pointed out that the parallel resistance and/or the saturation current under dark strongly influence the PCE of a photocell under low light illumination. In addition, the dependence of the device performance on the light intensity is found to be useful for analyzing the effects of the thermal treatment and the PFN interlayer at cathode. |
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| Keywords: | Conjugated polymer Unmodified fullerene Bulk heterojunction composites Halogen-free solvent Photocell Indoor light harvesting |
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