We report the effect of COOH-functionalized single walled carbon nanotubes (COOH-SWCNT) on the electrical and photovoltaic characteristics of Malachite Green (MG) dye based photovoltaic cells. Two different types of photovoltaic cells were prepared, one with MG dye and another by incorporating COOH-SWCNT with this dye. Cells were characterized through different electrical and photovoltaic measurements including photocurrent measurements with pulsed radiation. From the dark current—voltage (I–V) characteristic results, we observed a certain transition voltage (Vth) for both the cells beyond which the conduction mechanism of the cells change sharply. For the MG dye, Vth is 3.9 V whereas for COOH-SWCNT mixed with this dye, Vth drops to 2.7 V. The device performance improves due to the incorporation of COOH-SWCNT. The open circuit voltage and short circuit current density change from 4.2 to 97 mV and from 108 to 965 μA/cm2 respectively. Observations from photocurrent measurements show that the rate of growth and decay of the photocurrent are quite faster in the presence of COOH-SWCNT. This observation indicates a faster charge separation processes due to the incorporation of COOH-SWCNT in the MG dye cells. The high aspect ratio of COOH-SWCNT allows efficient conduction pathways for the generated charge carriers.

The influence of single walled carbon nanotube (SWCNT) on the series resistance (Rs) of Rose Bengal (RB) and Methyl Red (MR) dye-based organic diodes has been studied. It has been revealed from experimental results that SWCNT has a significant effect on Rs. The values of Rs are measured from current–voltage (I–V) characteristics and also by utilizing the Cheung method. Obtained values from the Cheung method have been verified using H(I)–I plots for all dye-based devices. The extracted values using these two processes show a good consistency with each other. It is observed that Rs is reduced significantly by incorporating SWCNT for both dyes. The estimated amounts of reduction of Rs using SWCNT are 76.08% and 64.23% obtained from the I–V relationship whereas the value of Rs shows a reduction of 83.5% and 67.1% when measured by using the Cheung method for RB and MR dyes respectively. The ideality factor and barrier height of the diodes have also been extracted. The ideality factor has decreased with incorporation of SWCNT. A reduction in barrier height for the devices has also been observed in the presence of SWCNT.

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Evening twilight airglow emissions of OH (7,2) band and Li 6708 A are observed by DunwManring type photometer and following important results are obtained.(i) Intensity of OH (7,2) and Li (6708 A) decrease exponentially during evening twilight period. (ii) OH (7,2) band covaries with Li (6708 A) during evening twilight period. (iii) Empirical equations of OH (7,2) band with time is obtained. (iv) Possible explanations of such type of variations is also presented.

In this work, we investigated the effect of single walled carbon nanotubes (SWCNT) on the electrical and photovoltaic properties of methyl red (MR) dye based photoelectrochemical cell (PEC). MR dye based PEC with LiClO 4 as ion salt were fabricated with and without mixing SWCNT. The cells were characterized through electrical and optical measurements. The performance of the devices changed drastically in presence of SWCNT. The transition voltage and trap energy of the cells were estimated from the steady-state dark current voltage (I-V) analysis. The transition voltage and trap energy decreased for MR dye cell in presence of SWCNT. Open circuit voltage (V oc ), short circuit current (J sc ), fill factor (FF) and power conversion efficiency (η) increased due to the addition of SWCNT. Further measurement of the transient photocurrent showed that the growth and decay of photocurrent was quite faster in presence of SWCNT. The photocurrent decay with time was fitted for both the cells and found to follow a power law relation which indicates dispersive transport mechanism with exponential trap states distributed in between lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) levels. Possible interpretation is done on the lowering of trap energy with the photocurrent. These results suggest that SWCNT lowers the trap energy of the cells by providing efficient percolation pathways for the conduction of charges. It is expected that due to lowering of trap energy the residing time of the free carriers within the traps decreases. In other words, it may also be said that the charge recombination decreases. These factors affect the overall conduction of charges and improve the electrical and photovoltaic properties.