Abstract
We investigate the dark and illuminated current density-voltage (J/V) characteristics of poly(2-methoxy-5-(2’-ethylhexyloxy)1-4-phenylenevinylene) (MEH-PPV)/single-walled carbon nanotubes (SWNTs) composite photovoltaic cells. Using an exponential band tail model, the conduction mechanism has been analysed for polymer only devices and composite devices, in terms of space charge limited current (SCLC) conduction mechanism, where we determine the power parameters and the threshold voltages. Elaborated devices for MEH-PPV:SWNTs (1:1) composites showed a photoresponse with an open-circuit voltage Voc of 0.4 V, a short-circuit current density JSC of 1 µA/cm² and a fill factor FF of 43%. We have modelised the organic photovoltaic devices with an equivalent circuit, where we calculated the series and shunt resistances.
Highlights
Solar cells based on conjugated polymers [1,2] are attractive due to their potential for low-cost manufacture
The observed space-charge limited current (SCLC) of the photovoltaic cells is explained based on an effective exponential tail state for the polymer matrix, which is modified by the embedded single-walled carbon nanotubes (SWNTs)
The dark current density-voltage J/V characteristics in logarithmic scale are presented in MEH-PPV:SWNTs composite)
Summary
Solar cells based on conjugated polymers [1,2] are attractive due to their potential for low-cost manufacture. The typical diffusion length of excitons, is only around 20 nm [5], and important to maximise the interface area for a given device so as to increase the chances of excitons encountering the interface This fact, has investigated the development of bulk heterojunction organic solar cells containing blends of electrons and holes conducting materials, in which the fine detail of the structure creates the large interface area required [6]. Polymers have been used previously in photovoltaic cells, but the low electrons mobilities of most conjugated polymers only allows them for use as the hole conducting components in a blend with other materials, such as fullerene [7], organic dyes [9] or in the present work with carbon nanotubes (CNTs) In these composite materials, the photocurrent is typically increased by several orders of magnitudes with comparaison to polymer only devices. The observed space-charge limited current (SCLC) of the photovoltaic cells is explained based on an effective exponential tail state for the polymer matrix, which is modified by the embedded SWNTs
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