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Ibrahim M. ALROUGY Dai TAGUCHI Takaaki MANAKA
Electric field induced optical second harmonic generation (EFISHG) measurement at the laser wavelength of 1000nm and 1080nm is conducted to investigate the carrier behaviors in PCPDTBT and PC71BM bulk heterojunction organic solar cells (OSCs). We find that the response time for electrode charging through the external circuit in +1V and -1V are almost identical but the response time for the Maxwell-Wagner-type interfacial charging is different in +1V or -1V. We find that the accumulated charges of PC71BM is more than the accumulated charges of PCPDTBT and consequently affects the efficiency of the bulk heterojunction OSCs.
Masaya OHZEKI Shunjiro FUJII Hiromichi KATAURA Yasushiro NISHIOKA
We fabricated bulk heterojunction organic solar cells based on 1,2-dichlorobenzene solutions of poly[[4,8-bis[(2-ethylhexyl) oxy]benzo[1,2-b:4,5-b'] dithiophene-2,6-diyl] [3-fluoro-2-[(2-ethylhexyl) carbonyl]thieno [3,4-b]-thiophenediyl]] (PTB7): [6,6]-phenyl-C71-butyric-acid-methyl-ester (PTB7:PC71BM) with additional dimethyl sulfoxide (DMSO) and surfactants diiodooctane (DIO). The optimal weight ratios of DMSO and DIO relative to the total weight of PTB7:PC71BM were 13% and 3%, respectively, and the resulting solar cells exhibited an open circuit voltage of 0.72 V, short circuit current density of 15.63 mA/cm2, fill factor of 0.49, and power conversion efficiency of 5.47%. The surfaces of the active layers deposited with added DMSO and DIO were smoother than those of the layers without the added surfactants and consisted of smaller nanograins, which may have resulted in the improved solar cell performance.
Kosei HASHIBA Shunjiro FUJII Hiromichi KATAURA Yasushiro NISHIOKA
Organic solar cells are expected to have superior performance in terms of flexibility and low-cost fabrication. However, conventional organic solar cells usually have issues while using rare earth ITO materials and have poor long-term reliability. To seek possible solutions for these issues, we fabricated an inverted solar cell structure of PEN/PEDOT:PSS/PFN/PTB7:PC71BM/MoO3/Au, and found that the fabricated devices had considerably improved long-term reliability when stored in air without any surface passivation layer. The resultant conversion efficiency of the solar cell was 1.88%, and it decreased to 90% of its initial value after 100 h of storage in air.