| Summary: | 碩士 === 明志科技大學 === 電子工程系碩士班 === 106 === Higher efficiency of an organic photovoltaic (OPV) could be easily achieved by availing the theoretical open circuit voltage (Voc) which are limited by several loss mechanisms inherent in the system. In general, the VOC is grossly determined by the energy level difference of the donor and acceptor molecules and constrained by the Schottky barrier (SB) heights at the semiconductor-metal contacts. In this study, the inhomogeneous SB heights formed at the anode-semiconductor junction of a DTDCPB: C70 bulk heterojunction OPV have been investigated rigorously by measuring current density – voltage (J-V) and capacitance – voltage (C-V) characteristics of the device under a large temperature range of 100K to 300 K and by inserting an insulating layer and hole transporting layer of MoO3 with varied thickness. Experimental results show a continuous non-linear increase in SB heights with the decrease in temperature throughout the whole temperature range as opposed to the existence of double Gaussian SB heights distribution corresponding to low and high temperature zone respectively. The mismatch of the SB barrier heights estimated from the J-V and C-V data have been explained by considering the non-linear variation of SB heights with temperature in the theory of inhomogeneous SB at the metal-semiconductor contacts. The calculated barrier heights (at high temperature range) at the interface of the active layer (DTDCPB: C70) and anode increase as increasing the thickness of the insulator layer (5, 10, 15 nm) and yield the prediction of open-circuit voltage (Voc) matching the experimental values. In addition, we found that the Mott-Schottky relation is not generally appropriate to determine built-in potential and estimate the limitation of Voc in small molecular OPV at low temperature.
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