EFFECT OF RARE-EARTH DOPING ON THE ELECTRICAL AND PHOTOELECTRICAL PROPERTIES OF FURAZANO[3,4-B]PIPERAZINE (FP) THIN-FILM DEVICES

Schottky diodes of rare-earth, praseodymium (Pr)-doped and samarium (S m)-doped furazano[3,4-b]piperazine (FP), sandwiched between Al and ind ium-tin oxide (ITO) were made by a spin-coating technique. The diodes, in which doped FP behaves as a p-type organic semiconductor, exhibit rectification behaviour, The p-type semiconductivity and rectification properties of the devices improve with rare-earth doping. The electri cal effects observed in these devices are explained in terms of the p- type semiconducting behaviour of the doped FP thin films and the forma tion of a blocking contact (Schottky barrier) with the Al electrode an d ohmic contact with the ITO electrode. Various electrical parameters such as carrier mobility, position of Fermi level, free carrier concen tration, trap density, trap level and conductivity of doped FP are cal culated and discussed. It is found that the position of the Fermi leve l shifts toward the valence band on rare-earth doping; concentration o f free carriers and carrier mobility increase on doping. From the capa citance-voltage (C-V) measurements, various electrical parameters such as barrier height, density of ionized acceptor atoms and depletion la yer width are calculated and discussed. From the action spectra and ab sorption spectra it is confirmed that the Al-doped FP interface forms a Schottky barrier and the ITO-doped FP interface shows ohmic contact. The photovoltaic measurement on the two devices reveals that the shor t circuit current, open circuit voltage, fill factor and power convers ion efficiency increase on rare-earth doping.