Electrically Detected Magnetic Resonance of MEH-PPV diodes
- PDF / 78,571 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 9 Downloads / 176 Views
P4.18.1
Electrically Detected Magnetic Resonance of MEH-PPV diodes George B. Silva, Lucas F. Santos1, Roberto M. Faria1, Carlos F. O. Graeff Departamento de Física e Matemática-FFCLRP-USP, Av. Bandeirantes 3900, 14040-901 Ribeirão Preto, Brazil 1-Instituto de Física de São Carlos-USP, C.P. 369, 13560-970 São Carlos, Brazil ABSTRACT In this work electrically detected magnetic resonance (EDMR) is used to study the electronic properties of poly(2-methoxy-5-(2'-ethyl-hexoxy)-1,4-phenylene vinylene) (MEHPPV) diodes. Two kinds of MEH-PPV diodes were characterized. The first one was a bipolar light emitting diode whose structure was ITO/MEH-PPV/Al. In this diode the EDMR signal is composed of two lines, a line that can be fitted by a lorentzian with peak-to-peak linewidth of 5.0 ± 0.5 G and the other best fitted with gaussian line with a linewidth of 24 ± 1 G. The g factor of both components is 2.002 ± 0.001 and signals were only observed at forward bias. The second diode is a hole only device, with a structure ITO/MEH-PPV/Au, the EDMR signal in this case is dominated by a gaussian line with peak-to-peak linewidth of 5 ± 1 G and average g factor of 2.0014 ± 0.0002. In high forward bias (V > 30 volts at T = 130K) a second line could be observed with a linewidth of 10 ± 2 G and a g factor of 2.0012 ± 0.0004. The signal from both types of diodes is quenching, and tipically10-5 in amplitude. The EDMR signal is assigned to the spin-dependent fusion of two like-charged polarons. Our results indicate that the narrower component is coming from positive polarons while the broader to negative polarons.
INTRODUCTION Light-emitting diodes (LEDs) based on conjugated polymers are interesting devices for applications requiring large areas such as in displays [1]. Among the various polymers used for LEDs and specially for displays, poly(2-methoxy-5-(2'-ethyl-hexoxy)-1,4-phenylene vinylene) (MEH-PPV) is one of the most promising, due to its good solubility, and easiness to process and the high efficiency of LEDs based on this material [2]. The detailed understanding of carrier injection and transport in these devices is of fundamental importance. Electrically detected magnetic resonance (EDMR) has provided insight into various transport and recombination mechanisms in both organic and inorganic semiconductors [3-10]. Normally in an EDMR experiment, microwave-induced changes in the conductivity are measured as the sample is subjected to a varying magnetic field. The EDMR signal comes from transport (for example hopping) or recombination processes, which are spin-dependent. Of special interest when studying devices, compared to standard Electron Spin Resonance (ESR), EDMR has proven to be more sensitive in detecting paramagnetic states [8]. In a previous work we have investigated ITO/MEH-PPV/Al diodes [10]. Those preliminary results indicated that the EDMR signal coming from such bipolar devices were composed of two contributions that were assigned to negatively and positively charged polarons. In this work, EDMR is applied to a homopolar
Data Loading...
