Spin dynamics of carrier generation in a photoconductive C60-doped poly(N-vinylcarbazole) film

Photocurrent enhancements in a porphyrin-viologen linked compound under plasmonic and magnetic fields

Zinc-porphyrin( ZnP )–viologen(V2+) linked compound containing six methylene group ( ZnP (6) V )–silver nanoparticle ( AgNP ) composite films was fabricated by combining electrostatic layer-by-layer adsorption and the Langmuir–Blodgett method. The incident photo to photocurrent efficiency (IPCE) values of the ZnP (6) V – AgNP composite films are higher than those of the ZnP (6) V films and much higher than those of ZnP derivative films without V2+moiety as a reference. The large increase in the IPCE values of the ZnP (6) V – AgNP composite films likely comes from a combination of localized surface plasmon resonance (LSPR) from AgNPs and photoinduced intramolecular electron-transfer upon linking to a V2+moiety. The photocurrents of the ZnP (6) V – AgNP composite films and the ZnP (6) V films increase upon application of a magnetic field. Magnetic field effects (MFEs) were clearly observed for both ZnP (6) V – AgNP composite films and the ZnP (6) V films. Photocurrents increase with magnetic field under low magnetic fields (B ≤ 150–300 mT) and are constant under high magnetic fields (B > 150–300 mT). MFEs can be explained by a radical pair mechanism. The magnitude of the MFEs in the ZnP (6) V – AgNP composite films is higher than that in the ZnP (6) V films. A remarkable increase in photocurrent for the ZnP (6) V – AgNP composite films was observed because of LSPR from the AgNPs in the presence of a magnetic field when compared with the ZnP (6) V films in the absence of a magnetic field.

Magneto-optical investigations on the formation and dissociation of intermolecular charge-transfer complexes at donor-acceptor interfaces in bulk-heterojunction organic solar cells

The electron-hole pairs can be formed in intermolecular charge-transfer (CT) states between two adjacent molecules due to Coulomb interaction in organic semiconducting materials. In general, the exciton dissociation can experience the intermediate states: intermolecular CT states at the donor-acceptor interfaces to generate a photocurrent in organic solar cells. This article reports the magneto-optical studies on intermolecular CT states in the generation of photocurrent by using magnetic field effects of photocurrent (MFE(PC)) and light-assisted dielectric response (LADR). The MFE(PC) and LADR studies reveal that internal electrical drifting and local Coulomb interaction can largely change the formation and dissociation of CT states by changing internal charge-transport channels and local Coulomb interaction through morphological development upon thermal annealing. Therefore, the MFE(PC) and LADR can be used as effective magneto-optical tools to investigate charge recombination, separation, and transport in organic solar cells.

Magnetoconductivity and magnetoluminescence studies in bipolar and almost hole-only sandwich devices made from films of a π-conjugated molecule

We present magnetoconductivity and magnetoluminescence measurements in sandwich devices made from films of a π-conjugated molecule and demonstrate effects of more than 30 and 50% magnitude, respectively, in fields of 100 mT at room-temperature. It has previously been recognized that the effect is caused by hyperfine coupling, and that it is phenomenologically similar to other magnetic field effects that act on electron-hole pairs, which are well-known in spin-chemistry. However, we show that the very large magnitude of the effect contradicts present knowledge of the electron-hole pair recombination processes in electroluminescent π-conjugated molecules, and that the effect persists even in almost hole-only devices. Therefore, this effect is likely caused by the interaction of radical pairs of equal charge.