No abstract

In this work, bulk heterojunction solar cells based on 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]] and phenyl-C71-butyric-acid-methyl-ester were fabricated using 1,2-dichlolobenzene solutions containing different weight ratios of oleamide. The oleamide layers were self-assembled on the active layer surfaces during the solidification of the active layer after spin coating. A significant increase in open-circuit voltage was observed after the introduction of oleamide at the expense of short-circuit current density. The optimal performance of the solar cell was obtained by spin coating the active layer at 1000 rpm for 60 s using a 1,2-dichlolobenzene solution containing 3% oleamide. The solar cell exhibited a short-circuit current density, an open circuit voltage, a fill factor, and a power conversion efficiency of 13.95 mA/cm2, 0.79 V, 0.47, and 5.22%, respectively. These solar cell behaviors are discussed on the basis of results of morphological analysis by optical microscopy, atomic force microscopy, and surface energy analysis.

Nickel oxide (NiO) has become attractive as a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT :PSS) substitute in solar cells’ hole transport layers (HTLs). However, solar cells with NiO HTLs based on 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) and [6,6]-phenyl C71 butyric acid methyl ester (PC71BM) remain poorly characterized. We report the effects of NiO-layer thickness on the performance of glass/ITO/NiO/PTB7:PC71BM/LiF/Al-structured solar cells. Thickness was optimized by changing nickel acetate tetrahydrate concentration in 2-methoxyethanol solution used for spin-coating deposition. We achieved a power conversion efficiency of 3.78% at 0.2 M of nickel acetate tetrahydrate.

Organic solar cells are expected to have superior performance with flexibility and low cost fabrication. However, conventional organic solar cells usually have issues of using rare earth ITO and inferior long term reliability. To seek possible solutions for these issues, we fabricated an inverted solar cell with a structure of PEN/PEDOT:PSS/PFN/PTB7:PC71BM/MoO3/Au, and found that these devices had much improved long-term reliability when they were stored in air without any surface passivation layer. The resultant conversion efficiency of the solar cell was 1.88%, and the conversion efficiency continued to be almost independent of time even after 100 h of storage in air.

Bulk-heterojunction solar cells were fabricated using ternary blend 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-C61-butyric acid methyl ester (PC61BM):[6,6]-phenyl C71 butyric acid methyl ester (PC71BM) with different weight ratios between PC61BM and PC71BM. In all the solar cells, the overall weight ratio of polymer to fullerene was maintained at 1:1.5, while the composition of the fullerene component (PC61BM:PC71BM) was varied. The measurement results of the solar cell performance showed that the open-circuit voltage notably increased for PC61BM weight fractions between 10% and 90%, while it decreased at 100%. The short-circuit current showed the most significant increase in the PC61BM weight fraction range between 50% and 60%. A power conversion efficiency of 3.4% was achieved when the PC61BM weight fraction was between 50% and 60%. These results may suggest that the transport of the photoexcited electrons between the cathode and the PC61BM/PC71BM nanodomains was enhanced.