Field quenching in photoconductive CdS as possible reason to enhance <i>V</i><sub>oc</sub> and FF in thin‐film solar cells

Böer, Karl W.

doi:10.1002/pssa.200925291

Cited by 13 publications

(4 citation statements)

References 31 publications

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“…The additional voltage drop is absorbed by expanding the high-field domain [38]. This causes an almost doubling of the open circuit voltage [39] (Fig. 33).…”

Section: Stationary Domains Improve Efficiencies Of Solar Cellsmentioning

confidence: 99%

The importance of gold‐electrode‐adjacent stationary high‐field Böer domains for the photoconductivity of CdS

Böer

2015

Annalen der Physik

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When the electron density decreases stronger than linearly with the electric field in photoconductive CdS due to field quenching, high-field domains must occur that remain attached to either the cathode or anode in slit electrode geometry with blocking cathodes. These Böer domains 1 are easily seen by their shift in optical absorption due to the Franz-Keldysh effect and offer unique opportunities to analyze field dependent parameters within the range of constant electron density and electric field, such as the carrier density or mobility as a function of the field, and give information of the light dependent work function. They also provide insight why a 200Å thick cover layer of CdS on top of a CdTe solar cell increases its efficiency from 8 to 16% . The behavior of these Böer domains escapes conventional current voltage analyses except for their visual observation, while other high-field domains with their current fluctuations or oscillations are easily observed and are the subjects of thousands of publications and many books. In this review we will exclude detailed discussion of dynamic domains, but include some new specifics that help to understand the mechanisms of the Böer domains and their applications. Only properties at low optical excitation intensities are discussed that exclude Joules heating. Within the p-type regime of the anode-adjacent domain extremely steep electronic quenching signal becomes visible that could signalize an intrinsic donor level slightly above the middle of the band gap that may be responsible for not allowing CdS to ever become ptype by doping.

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“…The additional voltage drop is absorbed by expanding the high-field domain [38]. This causes an almost doubling of the open circuit voltage [39] (Fig. 33).…”

Section: Stationary Domains Improve Efficiencies Of Solar Cellsmentioning

confidence: 99%

The importance of gold‐electrode‐adjacent stationary high‐field Böer domains for the photoconductivity of CdS

Böer

2015

Annalen der Physik

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“…These domains limit the field at the junction interface below 80 kV/cm and thereby eliminate junction leakage. This causes an almost doubling of the open circuit voltage [39,44,45].…”

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confidence: 98%

“…Without a direct measurement of the field distribution in these stationary domains, their existence remains obscure. But since these domains have now gained major technical interest by explaining the important contribution of a thin CdS layer on top of a CdTe solar cell, to almost doubling its efficiency [39,44,45], it became important to further evaluate the stationary domains. This is the purpose of this paper.…”

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confidence: 99%

Stationary high‐field domains as tools to measure field‐dependent carrier densities and mobilities in CdS and work functions of blocking contacts

Böer

2012

Physica Status Solidi (b)

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It is shown that stationary high-field domains that occur in the range of negative differential conductivity, can be used to clearly identify field-quenched states in CdS. These are distinguished as cathode and anode-adjacent domains and permit an unambiguous determination of electron density and mobility as function of the electric field. The anode-adjacent domain permits additional insight into the high-field properties of CdS in a field range that is now stabilized in the prebreakdown range. Here one finds direct evidence, by using the spectral distribution of the photoconductivity within the domain, of inverting the CdS to p-type either by more complete quenching or by hole injection from the anode. Both types of stationary domains are determined by the work function of blocking contacts and thereby permit a closer analysis of the contact/CdS interface by shifting the space charge region away from the cathode to the bulk-side end of the domain. This allows a more precise determination of the dependence of the work function on the photoconductivity of the adjacent CdS. The field-of-direction (phase portrait) analysis of the time-independent transport and Poisson equations allows a simple classification of the two types of stationary high-field domains relating to the two singular points in the decreasing branch of the current-voltage characteristic. This permits a transparent discussion of the field distribution of these domains that can be directly observed by the Franz-Keldysh effect. Herewith the transition between cathode-to anode-adjacent domains as a function of the applied voltage can be directly followed.

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“…The origin of the photocurrent decrease at voltage biases larger than 10 V should be thermally assisted and is related to the high electric eld. Here maybe conformational changes of the octapod assembly, or charges that are emitted from trap states, could play a role, [24][25][26] but this effect needs further investigation.…”

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Cold field emission dominated photoconductivity in ordered three-dimensional assemblies of octapod-shaped CdSe/CdS nanocrystals

et al. 2013

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Semiconductor nanocrystals, especially their ordered assemblies, are promising materials for various applications. In this paper, we investigate the photoconductive behavior of sub-micron size, ordered three-dimensional (3D) assemblies of octapod-shaped CdSe/CdS nanocrystals that are contacted by overlay electron-beam lithography. The regular structure of the assemblies leads to photocurrent-voltage curves that can be described by the cold field electron emission model. Mapping of the photoconductivity versus excitation wavelength and bias voltage allows the extraction of the band gap and identification of the photoactive region in the voltage and spectral domain. These results have important implications for the understanding of photoconductive transport in similar systems.

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Field quenching in photoconductive CdS as possible reason to enhance V_oc and FF in thin‐film solar cells

Cited by 13 publications

References 31 publications

The importance of gold‐electrode‐adjacent stationary high‐field Böer domains for the photoconductivity of CdS

The importance of gold‐electrode‐adjacent stationary high‐field Böer domains for the photoconductivity of CdS

Stationary high‐field domains as tools to measure field‐dependent carrier densities and mobilities in CdS and work functions of blocking contacts

Cold field emission dominated photoconductivity in ordered three-dimensional assemblies of octapod-shaped CdSe/CdS nanocrystals

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Field quenching in photoconductive CdS as possible reason to enhance Voc and FF in thin‐film solar cells

Cited by 13 publications

References 31 publications

The importance of gold‐electrode‐adjacent stationary high‐field Böer domains for the photoconductivity of CdS

The importance of gold‐electrode‐adjacent stationary high‐field Böer domains for the photoconductivity of CdS

Stationary high‐field domains as tools to measure field‐dependent carrier densities and mobilities in CdS and work functions of blocking contacts

Cold field emission dominated photoconductivity in ordered three-dimensional assemblies of octapod-shaped CdSe/CdS nanocrystals

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Field quenching in photoconductive CdS as possible reason to enhance V_oc and FF in thin‐film solar cells