Double Extraction of Uniformly Generated Electron-Hole Pairs from Insulators with Noninjecting Contacts

Abstract

A simple physical model has been used to derive an approximate theory of the double extraction of uniformly generated electron-hole pairs from a photoconductor layer with noninjecting contacts. The theory predicts 4 regimes of current versus applied voltage behavior: (1) At low voltage, I∝V. (2) At higher voltage, a transition region between I∝V and I∝V1/2. (3) At still higher voltage, I∝V1/2. (4) At very high voltage (above a saturation value), I=constant. The model relates the extent of these regimes to the physical parameters of the system, viz., μpτp (mobility × lifetime product for holes), μnτn (mobility × lifetime product for electrons), and the layer thickness. Good agreement is obtained between the theory and measurements on lead oxide vidicons. The theory also provides some insight into the nature of the transient phenomena ``red fade'' and ``after image'' sometimes observed in the operation of lead oxide vidicons. At high light excitation levels, space-charge-limited currents are expected. In this case, two regimes of current versus applied voltage behavior can be predicted: (1) Below a saturation value of voltage, I∝V1/2. (2) Above a saturation value of voltage, I=constant. The reasons for the one-half power current-voltage relationships are distinctly different in the μτ-limited and the space-charge-limited cases. In addition, the dependence of current on light intensity in the space-charge-limited case is a three-quarter power relation whereas in the μτ-limited case the dependence is a linear one. Also, the saturation voltage varies as the one-half power of the light intensity in the space-charge-limited case and is independent of the light intensity in the μτ-limited case.

Mobility and fill factor correlation in geminate recombination limited solar cells

“…25 Dissociation-limited FF can thus be lower than the 0.25 or 0.38 minima of transport or space-charge-limited FF. Furthermore, the mobility range over which the FF increases is considerably larger for dissociation-limited systems.…”

Nano-engineering of hybrid organic heterojunctions with carbon nanotubes to improve photovoltaic performance

“…It is generally accepted that Ohmic conduction is due to the low intrinsic conductivity of the polymer. 18 The charge carrier conduction is increased with the increase of voltage up to a certain value called the transition voltage, V T, and above this V T the charge conduction is governed by Child's Law due to the space charge limited current (SCLC) conduction: Where  is the permittivity of the material which is taken to be 3.…”

Carrier drift-mobilities and solar cell models for amorphous and nanocrystalline silicon

“…We shall refer to this model as the "5-parameter" model because the larger of the carrier mobilities usually has no significant effect on its predictions. This model has been developed at some length elsewhere [2,5,6], and may be directly useful in some materials [7]. For a-Si:H, we think that two additional parameters are required to give a good account of as-deposited cells (before lightsoaking is significant).…”

“…The 7-parameter model is motivated by general arguments [2,5,6] that the spacecharge of slowly drifting holes is likely to Table 1. Based on ref.…”

“…Under the conditions present in solar cells, holes in hydrogenated amorphous silicon (a-Si:H) have drift mobilities more than 10 5 smaller than in c-Si, and recombination lifetimes about 10 2 smaller. The corresponding ambipolar diffusion lengths are around 0.1 µm.…”