Charge conduction process and photovoltaic effect in ITO/ArV/CHR/In p-n junction device

The present communication deals with the designing of a new p-n junction de vice made with 4,4'-aryl bipyridine, also known as aryl viologen (ArV), a p -type organic semiconductor and 3-diazophenyl, 4,5 dihydroxynaphthalene, 2, 7 disulphonic acid, disodium salt, commonly known as chromotrope 2R (CHR), a n-type organic semiconductor. The electrical and photoelectrical properti es of the fabricated p-n junction having configuration ITO/ArV/CHR/In was s tudied by analysing its current-voltage (J-V) characteristics, capacitance- voltage (C-V) characteristics in the dark and photoaction spectra. The anal ysis of dark current-voltage (J-V characteristics at room temperature has b een presented in order to elucidate the conduction mechanisms and to evalua te the device parameters. The charge transport conduction mechanism in forw ard biased condition in the low voltage region is described by the modified Schockley effect. For biases >1.0 V, the dark current is a space charge li mited current (SCLC) in the presence of exponentially distributed traps. Th e variation of 1/C-2 with voltage also shows the straight line at low frequ ency indicating the formation of p-n junction between ArV and CHR and the p otential barrier height is about 1.18 eV at room temperature which decrease s with the increase in temperature. The comparison of photoaction spectra w ith absorption spectra of the ArV-CHR layer reveals that photocurrent in th is device is due to the generation of excitons both in ArV and CHR. The exc itons generated in AN dissociated by electron transfer to CHR and those cre ated in CHR are ionised by hole transfer to the ArV This charge transfer ma y be driven by the offset between the electron affinities and ionisation po tentials of two semiconductors. (C) 2001 Elsevier Science B.V. All rights r eserved.