Abstract
Photoinduced space-charges in organic optoelectronic devices, which are usually caused by poor mobility and charge injection imbalance, always limit the device performance. Here we demonstrate that photoinduced space-charge layers, accumulated at organic semiconductor-insulator interfaces, can also play a role for photocurrent generation. Photocurrent transients from organic devices, with insulator-semiconductor interfaces, were systematically studied by using the double-layer model with an equivalent circuit. Results indicated that the electric fields in photoinduced space-charge layers can be utilized for charge generation and can even induce a photovoltage reversal. Such an operational process of light harvesting would be promising for photoelectric conversion in organic devices.
Highlights
Organic optoelectronic devices [1,2,3,4,5], including photovoltaic devices [6,7,8,9], usually suffer from space-charges inside them due to poor charge mobility [10] and charge injection imbalance [11], in spite of the advantages of low cost, flexibility and ease of fabrication for organic semiconductors.The space-charges can usually induce a DC photocurrent accompanied by two photocurrent transients with opposite polarities for thick organic thin-film devices [12]
To fully understand the metal/insulator/organic semiconductor/metal (MISM) devices with photocurrent transients, an equivalent circuit can be established as the inset
Assuming that the SL is adjacent to the cathode Al, the photo-generated excitons will be separated into free charges
Summary
The space-charges can usually induce a DC photocurrent accompanied by two photocurrent transients with opposite polarities for thick organic thin-film devices [12]. Metal/insulator/organic semiconductor/metal (MISM) devices were developed, which were found to be promising for transient photodetection [13], artificial retinas [12,14] and near electric-field detection for ferroelectric domains [15]. The underlying physics of how the space-charges influence device performance is still not very clear, especially for organic photovoltaic devices of which performance can be dramatically enhanced under certain conditions, by the addition of dielectric/ferroelectric components [20,21,22,23,24,25]
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