The authors report on a highly efficient small-molecule organic photovoltaic device employing a planar-mixed heterojunction structure with subphthalocyanine (SubPc) as the donor and C 70 as the acceptor. By changing the mixing ratio of SubPc and C 70 , the power conversion efficiency can be significantly improved from 1.8% to 6.0% under air mass 1.5 G solar illumination. From the internal quantum efficiency measurement, the highest carrier extraction is observed when an optimized weight ratio for SubPc to C 70 of 1:7 is used. Besides, atomic force microscopy images demonstrate that a good phase separation of the blend layer is realized under such an optimized mixing ratio. This phenomenon may contribute to the improved fill factor and hence the bulk resistance. As a result, the J SC of our device is significantly enhanced to 13.0 mA/cm 2 , which is almost twice the conventional value for planar heterojunction SubPc devices.
We find an explicit relation between the two known ways of generating an infinite set of local conserved charges for the string sigma model on AdS 5 × S 5 : the Bäcklund and monodromy approaches. We start by constructing the two-parameter family of Bäcklund transformations for the string with an arbitrary world-sheet metric. We then show that only for a special value of one of the parameters the solutions generated by this transformation are compatible with the Virasoro constraints. By solving the Bäcklund equations in a non-perturbative fashion, we finally show that the generating functional of the Bäcklund conservation laws is equal to a certain sum of the quasi-momenta. The positions of the quasi-momenta in the complex spectral plane are uniquely determined by the real parameter of the Bäcklund transform.
Here, an efficient subphthalocyanine (SubPc)/C60 heterojunction organic photovoltaic device is demonstrated by using MoO3 as the anodic buffer. In comparison with the device without any treatments, the insertion of MoO3 leads to a significant increase in open-circuit voltage due to a better energy level alignment of the SubPc, which is similar to the use of oxygen-plasma. In addition, MoO3 serves as an optical spacer to tune the SubPc/C60 interface at the optimum optical field distribution. As a result, the short-circuit current density is considerably improved as predicted using the simulation model based on the transfer matrix. A slightly increased fill factor implies the efficient hole extraction after the insertion of MoO3. Moreover, the device with MoO3 as anodic buffer shows an elongated lifetime as compared with the device with oxygen-plasma treatment.
A high open-circuit voltage (V OC ) of an organic photovoltaic device (OPV) has been realized using an ultrathin electron donor layer, 2,3-Bis(2-(diphenylamino)-9,99-spirobifluorene-7-yl)fumaronitrile (PhSPFN), which exhibits the most suitable and low-lying highest occupied molecular orbital (HOMO) to align between the anode and donor energy levels. The planar heterojunction OPV, represented as indium tin oxide electrode/PhSPFN/fullerene C 60 /bathocuproine/aluminum electrode shows high performance with a V OC of 0.91 V, short current density of 3.9 mA/cm 2 , fill factor of 56% and power conversion efficiency of 2% under an air-mass of 1.5 global illumination at 1 sun. In addition, the effect of the V OC change is discussed in terms of various donor materials. The V OC turns out to be restricted to the energetic alignment between the work function of the anode and the HOMO level, indicating that the optimization of V OC requires energetically good contact between the anode and organic materials.
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