Open‐Circuit Photovoltage and Charge Recombination at Semiconductor/Liquid Interfaces

Mao, D.; Kim, Kang‐Jin; Frank, Arthur J.

doi:10.1149/1.2054901

Cited by 13 publications

(13 citation statements)

References 9 publications

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“…where z is the number of electrons involved in the reaction; in this case, z equals 14. 104 In this case, E oc is expected to decrease with increasing concentration of oxidized species which is the same result obtained with the model presented in this paper.…”

Section: ) Electrode Preparationsupporting

confidence: 87%

“…Other models exist that explain charge recombination process at semiconductor/liquid interfaces. 104 For non-ideal semiconductor/liquid junctions, when [1] the Fermi-level is pinned at semiconductor/liquid junctions where the barrier height is invariant with the concentration of redox species and [2] the interfacial charge transfer controls the recombination current, the open-circuit photovoltage can be described as…”

Section: ) Theoretical Modelsmentioning

confidence: 99%

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The Influence of Surface Chemistry on the Photoelectrochemical Properties of FeS(2) Photoanodes

Qi¹

2000

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The recurring theme of this dissertation is the correlation between FeS 2 surface chemistry and key electrical and electronic properties of FeS 2. Efforts have been made to identify and characterize the FeS 2 surface, investigate the photoelectrochemistry of FeS 2 photoanodes under anhydrous and anoxic conditions, and investigate the influence of deliberate surface chemistry on FeS 2 photoelectrochemistry. Infrared reflection-absorption spectroscopy (IRRAS) was used to investigate a thin adsorbate layer on pyrite. The results showed that the combination of angledependent studies and computational efforts are a powerful tool for characterizing the pyrite surface. The photoelectrochemistry of FeS 2 photoanodes was investigated in an I-/I 3 acetonitrile electrolyte. The results revealed that the non-aqueous system was suitable for strictly anhydrous and anoxic photoelectrochemical studies. A model was proposed to explain the observed influence of concentration of dissolved I 2 on the photovoltage. A central component of the proposed model was that shunting was assumed to take place at physically distinct regions of the electrode and that mass-transport to and from these regions could be treated separately from mass-transport to the regions responsible for the rectifying behavior of the FeS 2 /liquid junction. The implication of the agreement between experimental and calculated J-E curves is that macroscopic photoelectrochemical investigations may underestimate the quality of FeS 2 photoanodes due to the presence of defects. ii The influence of surface treatments on FeS 2 photoelectrochemistry was further studied using non-coordinating redox species. A statistically significant increase of photovoltage was observed after treating FeS 2 surfaces with KCN. X-ray photoelectron spectroscopy was used to study chemical bond formation between the electron donating ligands and iron(II) centers on the pyrite surface. The results were discussed in terms of charge recombination models and surface coordination chemistry. Unfinished work is also presented. Cathodic polarization in acidic media is a prerequisite for any detectable photoresponse. The exact function of the electrochemical activations was further investigated by electropolishing pyrite electrode under different experimental conditions including etchant identity and applied bias. The results suggested that the electrochemical treatment removes the damaged surface layer caused by mechanical polishing, and might also stabilize the surface states. Further experiments can be focus on anhydrous etching of pyrite photoanode. The research presented in this dissertation guides future studies of thin film FeS 2 photovoltaics. iii Dedication This dissertation is dedicated to my family. iv Acknowledgments I wish to express my sincere gratitude to my advisor Prof. Erik Johansson. His broad knowledge and logical way of thinking have been of great value for me. The present dissertation would not have been possible without his encouragement and supervision. I would like to thank Pro...

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Section: ) Electrode Preparationsupporting

confidence: 87%

Section: ) Theoretical Modelsmentioning

confidence: 99%

The Influence of Surface Chemistry on the Photoelectrochemical Properties of FeS(2) Photoanodes

Qi¹

2000

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“…All electrodes were etched, prior to use, with HF solution (49% by mass), as shown earlier [16]. The electrode was immersed in the HF solution for about 20 s, rinsed with distilled water, and then washed with methanol.…”

Section: Electrode Fabricationmentioning

confidence: 99%

Modification of n-Si Characteristics by Annealing and Cooling at Different Rates

Salih

Hilal

Sa'deddin

et al. 2003

Active and Passive Electronic Components

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The effect of annealing of the n-Si semiconductor on its characteristics in photoelectrochemical systems has been investigated. The annealing improved the dark current density vs. potential plots. The surface was improved by annealing, as manifested by SEM results. The effect of the cooling rate on preheated n-Si wafers was also investigated. It was found that the slowly cooled electrodes gave better dark current density vs. potential plots, for samples annealed at lower than 550 C. For samples annealed at higher temperatures, quenching gave better dark-current density vs. potential plots. SEM measurements showed parallel results to these findings. Enhanced surface textures were observed for slowly cooled wafers from temperatures below 550 C. Samples quenched from temperatures above 550 C showed better surfaces than slowly cooled counterparts.

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“…43,45 Voc/E 0 ' < 1 can be ascribed to defects present at the semiconductor/liquid interface. 32,43 Given that all redox couples' concentrations were approximately equal for reduced and oxidized species and across the electrolytes, Voc/E ≈ Voc/E 0 '. 45 The J-V data in Figure 8 and on pages 22-24 are consistent with the following explanations: 1) a Schottky-junction at the p-type QD solid/electrolyte interface (see Figure 4), 2) a rectifying junction at an FTO/n-type QD solid interface, and 3) partial n-type doping of the QD solid to yield a buried p-n junction.…”

Section: A) Results and Discussionmentioning

confidence: 99%

“…shown to affect open-circuit voltages by allowing for unwanted charge-carrier recombination within light absorbing material. [32][33][34][35] For PbS QD solids, specifically, it has been shown that non-optimal QD surface chemistry leads to, among other things, greater densities of sub-bandgap states. 36 Surface defects affect the performance of photovoltaic devices through charge-carrier recombination, but also through Fermi-level pinning.…”

Section: Ii) Introductionmentioning

confidence: 99%

Development of a Liquid Contacting Method for Investigating Photovoltaic Properties of PbS Quantum Dot Solids

Dereviankin¹

2000

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Photovoltaic (PV) devices based on PbS quantum dot (QD) solids demonstrate high photon-to-electron conversion yields. However, record power conversion efficiencies remain limited mainly due to bulk and interfacial defects in the light absorbing material (QD solids). Interfacial defects can be formed when a semiconductor, such as QD solid, is contacted by another material and may predetermine the semiconductor/metal or semiconductor/metal-oxide junction properties. The objective of the work described in this dissertation was set to explore whether electrochemical contacting using liquid electrolytes can provide sufficient means of contacting the QD solids to investigate their PV performance without introducing the unwanted interfacial defects. I have initially focused on optimizing processing conditions for efficient QD solids deposition and studied their photovoltaic properties in a standardized solid-state, depleted heterojunction solar cell configuration. Further, a liquid contacting method was developed to study the relationship between photovoltages of QD solids and the energetics (e.g. reduction potentials) of the liquid contacting media. This electrochemical contacting of PbS QD solids was achieved by using anhydrous liquid electrolytes containing fast, non-coordinating, outer-sphere redox couples. Depending on the energetics of a redox couple, both rectifying and nonrectifying (Ohmic) PbS QD solid/electrolyte junctions were successfully formed with both p-and n-type QD solids. Furthermore, application of the liquid solution contacting method in studies of the PbS QD solids has unprecedentedly demonstrated that an ideal behavior of the photovoltage changes with respect to the changes in the energetics of the contacting media can be achieved. This fact supports the initially proposed hypothesis that such liquid

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Open‐Circuit Photovoltage and Charge Recombination at Semiconductor/Liquid Interfaces

Cited by 13 publications

References 9 publications

The Influence of Surface Chemistry on the Photoelectrochemical Properties of FeS(2) Photoanodes

The Influence of Surface Chemistry on the Photoelectrochemical Properties of FeS(2) Photoanodes

Modification of n-Si Characteristics by Annealing and Cooling at Different Rates

Development of a Liquid Contacting Method for Investigating Photovoltaic Properties of PbS Quantum Dot Solids

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