Recently, power conversion efficiencies of organic photovoltaics based on small molecules have been dramatically improved by means of the bulk heterojunction (BHJ) structure. Moreover, to optimize photovoltaic perform...Recently, power conversion efficiencies of organic photovoltaics based on small molecules have been dramatically improved by means of the bulk heterojunction (BHJ) structure. Moreover, to optimize photovoltaic performance, thermal annealing treatments have often been used because of the simplicity of the process. However, the elucidation of effects of thermal annealing treatment on BHJ film structure based on small molecules is still not enough. Here, we report the results of structural analysis with synchrotron radiation of α-sexithiophene:fullerene BHJ films before and after thermal annealing treatment. In particular, the open-circuit voltage was increased to as high as 0.72 V;moreover, the BHJ films based on α-sexithiophene and fullerene were also clearly crystallized by the thermal annealing treatment. In this study, we found that the optimal crystal size existed in BHJ films for high-performance organic photovoltaics.展开更多
In-situ impedance spectroscopy (IS) observations of the photoconductivity of the carriers induced by photo-irradiation in organic hetero-junction structured photovoltaic devices are presented. In the IS measurements, ...In-situ impedance spectroscopy (IS) observations of the photoconductivity of the carriers induced by photo-irradiation in organic hetero-junction structured photovoltaic devices are presented. In the IS measurements, the externally applied voltage and the dependence of the light intensity applied to the device were investigated. Analysis of the frequency characteristics which was measured by changing the light intensity shows there is a proportional relationship between the changes in the conductivities of the two components. The mobilities of the CuPc and C60 layers were calculated from the conductivities and were in the orders of 10﹣4 and 10﹣3 cm2/Vs, respectively.展开更多
The carrier dynamics in organic photovoltaic (OPV) cells were investigated by impedance spectroscopy. We introduced a novel impedance spectrum representation called dynamic modulus plot (DMP), which allowed us to obse...The carrier dynamics in organic photovoltaic (OPV) cells were investigated by impedance spectroscopy. We introduced a novel impedance spectrum representation called dynamic modulus plot (DMP), which allowed us to observe the layer-to-layer carrier injection behavior graphically. In this work, the impedance responses were characterized in the N,N’-diphenyl-N,N’-di-m-tolyl- 4,4’-diaminobiphenyl (TPD)/C60 p-n heterostructured OPV cells against applied voltages. The dependence of impedance responses on the layer thickness revealed a constant internal electric field that disturbed the carrier transport within the OPV cells. We applied this technique to new donor materials, in which thiophene units were inserted to the center of TPD. By increasing the number of thiophene units in TPD the fill-factor (FF) improved from 33% to 59%, which increased the power conversion efficiency (PCE). Based on the DMP analysis, we assigned the improvement in device performance to the reduction of the internal electric field.展开更多
The effect of the molecular structure on photovoltaic performance was investigated by comparing two types of active layers. One is an active layer formed by sexithiophene (6T) and C60 molecules which don’t have side ...The effect of the molecular structure on photovoltaic performance was investigated by comparing two types of active layers. One is an active layer formed by sexithiophene (6T) and C60 molecules which don’t have side chains. Another one is an active layer formed by a,ω-bis(2-hexyldecyl)sexithiophene (BHD6T) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) molecules which have side chains. The 6T:C60 active layer exhibited an excessive crystallization of 6T, which led to the low photovoltaic performance. In the BHD6T:PCBM active layer, the crystallization of BHD6T was suppressed. The crystallization of BHD6T was also easily controlled by thermal annealing, which led to improved photovoltaic performance.展开更多
Crystallization of amorphous poly(lactic acid) (PLA) was investigated by exposing to vapor of acetone. The vapor of acetone induced crystallization of the amorphous PLA effectively. It took about 24 min to complete th...Crystallization of amorphous poly(lactic acid) (PLA) was investigated by exposing to vapor of acetone. The vapor of acetone induced crystallization of the amorphous PLA effectively. It took about 24 min to complete the crystallization of a 1 cm × 2 cm × 0.55 mm specimen at 25℃. The crystallization rate increased with increasing of conducting temperature. The crystallization method yielded high crystallinity about 40%, which was almost equal to that attained by annealing or immersion methods conducted as references. The specimens crystallized by the vapor showed higher transparency than those prepared by the reference methods. The crystallization was induced by diffusion of acetone into the amorphous phase of PLA, and polarized optical photomicrographs cleared that the diffusion obeyed Fick type diffusion.展开更多
文摘Recently, power conversion efficiencies of organic photovoltaics based on small molecules have been dramatically improved by means of the bulk heterojunction (BHJ) structure. Moreover, to optimize photovoltaic performance, thermal annealing treatments have often been used because of the simplicity of the process. However, the elucidation of effects of thermal annealing treatment on BHJ film structure based on small molecules is still not enough. Here, we report the results of structural analysis with synchrotron radiation of α-sexithiophene:fullerene BHJ films before and after thermal annealing treatment. In particular, the open-circuit voltage was increased to as high as 0.72 V;moreover, the BHJ films based on α-sexithiophene and fullerene were also clearly crystallized by the thermal annealing treatment. In this study, we found that the optimal crystal size existed in BHJ films for high-performance organic photovoltaics.
文摘In-situ impedance spectroscopy (IS) observations of the photoconductivity of the carriers induced by photo-irradiation in organic hetero-junction structured photovoltaic devices are presented. In the IS measurements, the externally applied voltage and the dependence of the light intensity applied to the device were investigated. Analysis of the frequency characteristics which was measured by changing the light intensity shows there is a proportional relationship between the changes in the conductivities of the two components. The mobilities of the CuPc and C60 layers were calculated from the conductivities and were in the orders of 10﹣4 and 10﹣3 cm2/Vs, respectively.
文摘The carrier dynamics in organic photovoltaic (OPV) cells were investigated by impedance spectroscopy. We introduced a novel impedance spectrum representation called dynamic modulus plot (DMP), which allowed us to observe the layer-to-layer carrier injection behavior graphically. In this work, the impedance responses were characterized in the N,N’-diphenyl-N,N’-di-m-tolyl- 4,4’-diaminobiphenyl (TPD)/C60 p-n heterostructured OPV cells against applied voltages. The dependence of impedance responses on the layer thickness revealed a constant internal electric field that disturbed the carrier transport within the OPV cells. We applied this technique to new donor materials, in which thiophene units were inserted to the center of TPD. By increasing the number of thiophene units in TPD the fill-factor (FF) improved from 33% to 59%, which increased the power conversion efficiency (PCE). Based on the DMP analysis, we assigned the improvement in device performance to the reduction of the internal electric field.
文摘The effect of the molecular structure on photovoltaic performance was investigated by comparing two types of active layers. One is an active layer formed by sexithiophene (6T) and C60 molecules which don’t have side chains. Another one is an active layer formed by a,ω-bis(2-hexyldecyl)sexithiophene (BHD6T) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) molecules which have side chains. The 6T:C60 active layer exhibited an excessive crystallization of 6T, which led to the low photovoltaic performance. In the BHD6T:PCBM active layer, the crystallization of BHD6T was suppressed. The crystallization of BHD6T was also easily controlled by thermal annealing, which led to improved photovoltaic performance.
文摘Crystallization of amorphous poly(lactic acid) (PLA) was investigated by exposing to vapor of acetone. The vapor of acetone induced crystallization of the amorphous PLA effectively. It took about 24 min to complete the crystallization of a 1 cm × 2 cm × 0.55 mm specimen at 25℃. The crystallization rate increased with increasing of conducting temperature. The crystallization method yielded high crystallinity about 40%, which was almost equal to that attained by annealing or immersion methods conducted as references. The specimens crystallized by the vapor showed higher transparency than those prepared by the reference methods. The crystallization was induced by diffusion of acetone into the amorphous phase of PLA, and polarized optical photomicrographs cleared that the diffusion obeyed Fick type diffusion.
