Charge Generation Recombination Research Articles

Unraveling Device Physics of Dilute-Donor Narrow-Bandgap Organic Solar Cells with Highly Transparent Active Layers.

The charge generation-recombination dynamics in three narrow-bandgap near-IR absorbing nonfullerene (NFA) based organic photovoltaic (OPV) systems with varied donor concentrations of 40%, 30%, and 20% are investigated. The dilution of the polymer donor with visible-range absorption leads to highly transparent active layers with blend average visible transmittance (AVT) values of 64%, 70%, and 77%, respectively. Opaque devices in the optimized highly reproducible device configuration comprising these transparent active layers lead to photoconversion efficiencies (PCEs) of 7.0%, 6.5%, and 4.1%. The investigation of these structures yields quantitative insights into changes in the charge generation, non-geminate charge recombination, and extraction dynamics upon dilution of the donor. Lastly, this study gives an outlook for employing the highly transparent active layers in semitransparent organic photovoltaics (ST-OPVs).

Solution-Processed Semitransparent Organic Photovoltaics: From Molecular Design to Device Performance.

Recent research efforts on solution-processed semitransparent organic solar cells (OSCs) are presented. Essential properties of organic donor:acceptor bulk heterojunction blends and electrode materials, required for the combination of simultaneous high power conversion efficiency (PCE) and average visible transmittance of photovoltaic devices, are presented from the materials science and device engineering points of view. Aspects of optical perception, charge generation-recombination, and extraction processes relevant for semitransparent OSCs are also discussed in detail. Furthermore, the theoretical limits of PCE for fully transparent OSCs, compared to the performance of the best reported semitransparent OSCs, and options for further optimization are discussed.

Photo-Hall-Effect Spectroscopy with Enhanced Illumination in p−Cd1−xMnxTe Showing Negative Differential Photoconductivity

We studied deep levels (DLs) in p-type CdMnTe by photo-Hall effect spectroscopy with enhanced illumination. We showed that the mobility of minority and majority carriers can be deduced directly from the spectra by using proper wavelength and excitation intensity. Four deep levels with ionization energies 0.63 eV, 0.9 eV, 1.0 eV and 1.3 eV were detected and their positions in the bandgap were verified by comparison of photogenerated electron and hole concentrations. Deduced DL model was analyzed by numerical simulations with Shockley-Reed-Hall charge generation-recombination theory and compared with alternative DL models differing in the position of selected DLs relative to Ec and Ev. We showed that the consistent explanation of collected experimental data principally limits the applicability of alternative DLs models. We also demonstrated the importance of the extended operation photon fluxes used in the spectra acquisition for correct determination of DLs character. Negative differential photoconductivity was observed and studied by charge dynamic theoretical simulations.

Electric-field-assisted bipolar charge generation from internal charge separation zone composed of doped organic bilayer

For studying the mechanism of electric-field-assisted bipolar charges spouting from an internal charge separation (ICS) zone, three different categories of organic thin-film devices, which contain p-n heterojunction bilayer of tetrafluorotetracyanoquinodimethane-doped N,N′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine and Mg-doped tris(8-quinolinolato)aluminum(III) for the ICS zone, have been fabricated. The bipolar charge separation mechanism in p- and n-doped organic bilayer system was explained in terms of the charge generation-recombination mechanism used in traditional inorganic p-n homojunction diodes.

Conductivity of water-in-oil microemulsions: Fluctuations from the charge generation-recombination equilibrium

A theory for conductivity fluctuations in water-in-oil microemulsions is presented. The treatment is based on the charge fluctuations model proposed by Eicke et al., Hall, and Halle. The portion of current fluctuations due to fluctuations in the number of charge carriers is attributed to the charge generation-recombination equilibrium: two neutral drops ⇌ positive drop+negative drop. The power spectrum of the fluctuations is a Lorentzian determined by the forward and reverse rates of this equilibrium. Implications of the charge fluctuation model for experimental studies of water-in-oil microemulsions are suggested.

Measurement of space charge generation-recombination current in Hg 1− xCd xTe photodiodes by deep level transient spectroscopy

Deep Level Transient Spectroscopy (DLTS) measurements have been used to characterize n + − pHg 1− x Cd x Te junction photodiode performance. Deep level results obtained on a x = 0.320 liquid phase epitaxial grown photodiode and a x = 0.219 bulk quench anneal-grown photodiode have identified deep Shockley-Read recombination centers. Detailed characterization of trap energy, trap density, and capture cross sections for these traps located within the diode depletion region have been used to predict a space charge generation-recombination current and dynamic resistance-area product at zero bias voltage. This paper presents for the first time a direct correlation of DLTS parameters with photodiode device performance.