Abstract
We report the negative capacitance of nanocrystalline titanium dioxide/poly (3-hexyl thiophene), nc-TiO2/P3HT, heterojunction solar cells. In air, low frequency negative capacitance has been observed under forward bias associated with high values of conductance. Interestingly, the negative capacitance disappear when the device was placed in vacuum chamber. These results are attributed to affect the ambient conditions on the charge carrier concentration in materials used to fabricated solar cells and increase the bulk region resistance.
Highlights
In the last decades, many researchers have used small-signal admittance techniques to identify microscopic processes in electronic devices, for example, charges recombination and generation at interfacial areas such as metal/semiconductor or semiconductor/insulator (Zaki et al, 2013; Itoj and Nakagoshi, 2014; Taylor et al, 1991; Stallinga et al, 2002)
The negative capacitance was not observed in vacuum
It has been shown that the negative capacitance of nc-TiO2/P3HT, heterojunction cells is dependent on the ambient condition
Summary
Many researchers have used small-signal admittance techniques to identify microscopic processes in electronic devices, for example, charges recombination and generation at interfacial areas such as metal/semiconductor or semiconductor/insulator (Zaki et al, 2013; Itoj and Nakagoshi, 2014; Taylor et al, 1991; Stallinga et al, 2002). To explore the physical mechanisms at interfaces, studying capacitance characteristic of organic devices under different frequencies is a useful method to achieve that. One of these mechanisms is Negative Capacitance (NC) which appears in organic solar cells and light emitting diodes. This Phenomenon have attracted a lot of attentions. The appearance of NC in signal admittance measurements indicates the processes occurred at interfaces in organic electronic device either generation of exciton (electron-hole pair) in solar cells or recombination of exciton in light emitting diode. We found that the negative capacitance in P3HT/nc-TiO2 solar cells depends on the ambient conditions
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