A STUDY OF ORGANIC SEMICONDUCTOR POLYMER MATERIAL AND DEVICE STRUCTURES FOR APPLICATION IN OPTICAL DETECTORS

In this work, polymer photo-detectors having good electrical and optical characteristics have been demonstrated. It is shown that pure MEHPPV, an electroluminescent material can be used as active material in organic photodetector. Further, devices fabricated using blends of MEHPPV with PCBM as photoabsorbing layer has an order of improved photoresponse with respect to the device having only MEHPPV as active layer. The optimization of the processing conditions and change of device structure has been done in order to get good quality devices. It is shown that the use of aromatic solvent leads to best results. The photoresponse in the device with polymer dissolved in 1-2 Dichlorobenzene is found to be better with maximum ratio of photo current to dark current as 29.9 at -2.2 V, where as the leakage current in the device with MEHPPV dissolved in Chlorobenzene is less. The thickness variation of the active layer is incorporated and it is observed that photo-response is better in the device with thinner active layer. The maximum ratio of the photocurrent to the dark current is in the thinner device that is 29.51 at very low bias voltage of -0.8V.The leakage current is reduced to -9 x 10 A/ cm as the active polymer layer thickness is increased. The device using blend of MEHPPV: PCBM in 1:1 proportion shows a very high ratio of photocurrent density to dark current density that is 2324.07 at a very low applied bias of 0.6V. The physical demonstration of the photo-detector using MEHPPV: PCBM (1:4) as photoabsorbing layer using an OP-AMP photodetector circuit has been made. The response time of the detector at 680 Ω load was measured to be 450 ns and calculated capacitance value is 0.566 nF.