Optoelectronic conversion by polarization current, triggered by space charges at organic-based interfaces

Abstract

We report that a highly efficient optoelectronic conversion can be achieved by photogenerated space charges, which usually damp photocurrent. Theoretical analysis of metal-organic insulator-organic semiconductor-metal photocells indicates the generation of a large transient current that is triggered by photogenerated space charges and governed by the dielectric properties of the insulator layer. We experimentally demonstrated this mechanism with model photocells, revealing that the quantum efficiency can be dramatically increased by increasing the dielectric constant of the insulator.

Storage of an electric field for photocurrent generation in ferroelectric-functionalized organic devices

“…6b), large photocurrent transients (J tr ), consisting of an ON-state (J on ) and an OFF-state transient upon light on and off, with positive/negative directions, are detected for these devices. The positive J tr is caused by a light-induced charging process, while the negative J tr originates from the discharging or recovery process 20 . As can be seen, the polarities of the J tr induced by positive and negative poling are opposite to each other.…”

“…The multilayer devices were fabricated by similar techniques to those described previously 20,21 (see also the Methods section). First, we chose a symmetric MSFSM device structure, with aluminium (Al) as the electrodes, for study to avoid the influence of chemical reactions at each Al/P(VDF-TrFE) interface 19 .…”

“…Current-voltage characteristics and photocurrent transients 20,21 from metal/organic semiconductor/ferroelectric polymer/organic semiconductor/ metal (MSFSM) devices were utilized to characterize such fields, which are caused by incomplete compensation of the ferroelectric polarization that undergoes a multi-step polarization process. We note that the average net field, after becoming stable, is comparable with that produced by an electrode potential difference f. A prototype photodetector driven by these oriented stray fields is demonstrated with a photoresponsive memory effect, and a responsivity of B0.1 mA W À 1 under zero bias voltage (passive mode).…”

A route to high gain photodetectors through suppressed recombination in disordered films

“…1,2 Recently, innovative photodetector designs have been demonstrated, such as the use of an insulating layer to produce a high-frequency detector that is insensitive to background illumination. 3,4 Another advance has been the creation of narrowband detectors that use inefficient charge transport to engineer a sharp peak in external quantum efficiency (EQE) near the optical absorption edge of the active layer. 5,6 However, these designs and others 7,8 work by simply transporting the photogenerated charges through the device and have responsivities that are limited by the efficiencies of photon absorption, charge generation, and charge extraction.…”

Changing inter-molecular spin-orbital coupling for generating magnetic field effects in phosphorescent organic semiconductors

“…Therefore, both dissociation and charge reaction channels can be affected by matrix dielectric constant. On one hand, increasing matrix dielectric constant can increase the dissociation rates for both singlet and triplet polaron pairs through Onsager process 34,35 by changing the Onsager radius (R c ¼ e 2 4pe 0 eKT ). This minimizes the difference between singlet and triplet dissociation yields in polaron pairs.…”