Nonlinear Transient Photovoltaic Response in Al/C60/Au Devices: Control of Polarity with Optical Bias

We report fast (nanosecond) transient photovoltaic response and steady-state photovoltage of rectifying Al/C60/Au sandwich devices. The transient photovoltage changes polarity at a critical light intensity, which can be varied and controlled by applying steady-state light as bias. This ability to change the polarity of the transient photovoltaic response and to control the intensity at which the polarity changes sign offers potential for use in applications in the area of fast nonlinear optoelectronic detectors. Applied Physics Letters is copyrighted by The American Institute of Physics

Dynamics of Photoexcited Carriers in Pristine Oxygen-Free C60 Films: Study of the Time-Resolved Transient Photoconductivity

We study the dynamics of photoexcited carriers in pristine oxygen-free C60 films using the measurement of the transient photoconductivity (PC). The nonexponential relaxation of photocarriers in oxygen-free C60 can be described by the multiple trapping model. The carrier recombination kinetics is characteristic of bimolecular recombination at high temperature. As the thermally-activated long-lived PC component freezes out at the low temperature regime, a monomolecular recombination prevails and the carrier relaxation approaches an exponential decay. The peak transient PC exhibits a local maximum at T ≈ 240 K, near a first-order structural phase transition temperature, indicating that evaporated film of oxygen-free C60 contains regions of structurally ordered C60. The disorder in a pristine C60 film is manifested by the existence of a large, thermally-activated, long-lived PC component

Improvement of Raman Spectra of SAPO-5 by Chromium(III)-Induced Luminescence Quenching

Addition of small amounts of Cr(N03)3 x 9 H20 during the hydrothermal synthesis of SAPO-5 produced pseudooctahedrally coordinated chromium(III) species within the unidimemsional channel system of the molecular sieve. A broad intense photoluminescence that occurs in the visible region upon 532 nm photoexcitation of calcined SAPO-5 is efficiently quenched in Cr-SAPO-5 allowing for unobstructed detection of Raman scattering spectra. The photoluminescence quenching mechanism appears to involve an energy transfer from the molecular sieve photoexcited surface states to the metastable chromium(III) 2E state, giving rise to the well-known chromium(III) 2E - 4A2 luminescence at 696 nm

Effects of Oxygen on the Photocarrier Dynamics in a C60 Film: Studies of Transient and Steady-State Photoconductivity

The intrinsic dynamics of photoexcited carriers in an oxygen-free C60 film and their remarkable evolution as the film is exposed to oxygen are revealed by transient and steady-state photoconductivity (PC) measurements at various temperatures, light intensities, and photon energies. Exposure of C60 film to oxygen creates deep traps that reduce drastically the carrier lifetime and, consequently, the room-temperature steady-state photoconductivity by three to six orders of magnitude. Oxygen affects the steady-state photoconductivity excitation spectrum in a qualitatively similar way, as does decreasing the ambient temperature; in both cases, the photoconductivity decreases faster when carriers are photoexcited into the band edges. The transient and steady-state PC of a C60 film fully exposed to oxygen becomes temperature independent

Semiconducting Polymer-Buckminsterfullerene Heterojunctions: Diodes, Photodiodes, and Photovoltaic Cells

The characterization of rectifying heterojunctions (diodes) fabricated from a semiconducting polymer, a soluble derivative of poly(phenylene-vinylene), and buckminsterfullerene, C60, are reported. Rectification ratios in the current versus voltage characteristics exceed 104. When illuminated, the devices exhibit a large photoresponse as a result of photoinduced electron transfer across the heterojunction interface from the semiconducting polymer (donor) onto C60 (acceptor). The photodiode and photovoltaic responses are characterized. Photoinduced electron transfer across the donor-accepted rectifying heterojunction offers potential for photodetector and for solar cell applications

The Effect of Oxygen on the Photoconductivity of C60 Film: Action Spectrum and Temperature-Dependence

Abstract We report the effect of oxygen on the action spectrum of the steady-state photoconductivity (PC) of C60 film and its temperature dependence. The steady-state PC decreases more than 4 orders of magnitude upon exposure to oxygen; the PC decreases faster below ω≊2.3 eV. The low-temperature PC spectrum of the oxygen-free C60 is similar to the high-temperature PC spectrum of C60 exposed to oxygen. The steady-state PC exhibits a peak at T≊240 K in the oxygen-free C60, which disappears in C60 exposed to oxygen. The results indicate that the oxygen in C60 film acts as an efficient deep trap for photoexcited carriers and reduces the structural order