Stress-induced variation of MDMO-PPV film thickness and resistance

- The mechanic and electrical properties of MDMO-PPV are measured.
- Stress tightens MDMO-PPV and makes it more conductive.
- The maximum piezoresistance coefficient is 4.36 × 10−3 Pa−1.
- Conductive mechanism changes from TCLC to Ohm's law after tightening.

The loading curves and Young's modulus of poly(2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylenevinylene) (MDMO-PPV) films have been measured using nanoindentation through single- and multicycle- test. The ITO\MDMO-PPV\Al devices were fabricated and measured. We measured the I-V characteristics of the devices under different stresses. We found that the applied stress makes the film not only tightened but also more conductive. The devices showed a good piezoresistive performance. Their piezoresistance coefficients have even reached 4.36 × 10−3 Pa−1. The device resistance significantly decreased with the periodical stress produced by a weight, demonstrating a good sensitivity, stability, and repeatability. We propose that two mechanisms are involved in the I-V characteristics in the bias range from 0 to 4 V. One is the Ohm's law, which is taking effect at low current density or high stress (more than 118 kPa); the other is the trapped charge limited current (TCLC) mechanism, which is taking effect at high current density and low stress (less than 118 kPa).