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Photovoltaic properties of bulk heterojunction devices based on CuI-PVA as electron donor and PCBM and modified PCBM as electron acceptor

Sharma G. D., Shanap T. S., Patel K. R., El-Mansy M. K.

Materials Science Poland

2012

Vol. 30, No. 1

10--16

In this paper, we have investigated the bulk heterojunction organic solar cells based on CuI - polyvinyl alcohol (CuI-PVA) nanocomposite as electron donor and [6,6] - phenyl C60 - butyric acid methyl ester (PCBM) or modified PCBM i.e. F as electron acceptor. The power conversion efficiencies (PCEs) of 0.46 % and 0.68 % were achieved for the photovoltaic devices based on as cast CuI-PVA:PCBM and CuI-PVA:F blend films, respectively. The higher PCEs of the organic solar cells based on F as electron acceptor resulted from the increase in both short circuit current (Jsc) and open circuit voltage (Voc), due to the increased absorption of F in visible region and its higher LUMO level. After thermal annealing, the PCEs of the organic solar cells were further increased to 0.54 % and 0.80 % for CuI-PVA:PCBM and CuI-PVA:F blends, respectively. The increase in the PCEs was mainly due to the increase in Jsc, which has been attributed to the improvement in hole mobility and broadening of the absorption band in the longer wavelength region. The improved hole mobility resulted in more balanced charge transport in the devices based on the thermally annealed blends.

Mechanism of charge generation and photovoltaic effects in lead phthalocyanine based Schottky barrier

Sharma G. D., Choudhary V. S., Janu Y., Roy M. S.

Materials Science Poland

2007

Vol. 25, No. 4

1173--1191

Photovoltaic properties of lead phtalocyanine (PbPc) thin films sandwiched between indium tin oxide (ITO) and aluminum electrodes (ITO/PbPc/Al) have been investigated. The J-V characteristics of the device reveals that current flow across the device is limited by hole injection at Al/PbPc below 300 K, wherein Al is kept at higher bias. Junction parameters such as built-in potential (Vbi), carrier concentration (Na), the width of depletion layer (W) were evaluated from the C-V measurements. The mechanism of transport of carriers in Al/PbPc/ITO has been investigated based on the detailed analysis of current- voltage characteristics at various temperatures in the dark. The PbPc form hole injection barriers with both Al and ITO electrodes which are 0.88 eV and 0.11 eV, respectively, indicating the formation of nearly Ohmic contact with ITO and the Schottky barrier with Al. The photovoltaic parameters of the device have been estimated from the analysis of the current-voltage characteristics under illumination and discussed in detail. Electrically active defects were investigated by the space charge capacitance spectroscopy methods at various temperatures (from 250 K to 350 K) and frequencies (from 5 Hz to 1 MHz), respectively. The activation energy calculated from the capacitance spectroscopy at various temperatures is about 0.32 eV suggesting that the defects originate from the trapping centres at Al/PbPc interface.