The Spatial Collection Efficiency of Charge Carriers in Photovoltaic and Photoelectrochemical Cells

Segev, Gideon; Dotan, Hen; Ellis, David S.; Piekner, Yifat; Klotz, Dino; Beeman, J. W.; Cooper, Jason K.; Grave, Daniel A.; Sharp, Ian; Rothschild, Avner

doi:10.1016/j.joule.2017.12.007

Cited by 43 publications

(78 citation statements)

References 59 publications

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“…The origin of this discrepancy most likely arises from the inability to extract the photogenerated charge carriers due to recombination in thicker films, [30] or the lack of asymmetry for charge transport and collection. [31] In order to reduce these electrical losses, heterogeneously doped hematite photoanodes with the following doping profile were fabricated: 1 cat% Zn -undoped -1 cat% Ti doped. [13] The light and dark current densities of heterogeneously doped hematite photoanodes with hematite thickness of 9 and 14 nm are depicted in Figure S13b (Supporting Information).…”

Section: Ultrathin Optical Aborbersmentioning

confidence: 99%

Film Flip and Transfer Process to Enhance Light Harvesting in Ultrathin Absorber Films on Specular Back‐Reflectors

et al. 2018

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Optical interference is used to enhance light-matter interaction and harvest broadband light in ultrathin semiconductor absorber films on specular back-reflectors. However, the high-temperature processing in oxygen atmosphere required for oxide absorbers often degrades metallic back-reflectors and their specular reflectance. In order to overcome this problem, a newly developed film flip and transfer process is presented that enables high-temperature processing without degradation of the metallic back-reflector and without the need of passivation interlayers. The film flip and transfer process improves the performance of photoanodes for photoelectrochemical water splitting comprising ultrathin (<20 nm) hematite (α-Fe O ) films on silver-gold alloy (90 at% Ag-10 at% Au) back-reflectors. Specular back-reflectors are obtained with high reflectance below hematite films, which is necessary for maximizing the productive light absorption in the hematite film and minimizing nonproductive absorption in the back-reflector. Furthermore, the film flip and transfer process opens up a new route to attach thin film stacks onto a wide range of substrates including flexible or temperature sensitive materials.

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Section: Ultrathin Optical Aborbersmentioning

confidence: 99%

Film Flip and Transfer Process to Enhance Light Harvesting in Ultrathin Absorber Films on Specular Back‐Reflectors

et al. 2018

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“…Evaluating the spatial collection efficiency (SCE), i.e., the yield with which locally photogenerated charge carriers contribute to the photocurrent, has been used to study other types of photovoltaic devices such as crystalline Si, GaAs, CdS/CdTe, CIGS, as well as photoelectrochemical cells . Extending this characterization tool to new device architectures, such as CQD, perovskite, and organic solar cells, remains a challenge due to the complex effect of thin‐film interference, for this effect precludes the use of conventional analytical methods in the calculation of the SCE.…”

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confidence: 99%

Spatial Collection in Colloidal Quantum Dot Solar Cells

Ouellette

Lesage‐Landry

Scheffel

et al. 2019

Adv Funct Materials

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In thin-film photovoltaic (PV) research and development, it is of interest to determine where the chief losses are occurring within the active layer. Herein, a method is developed and presented by which the spatial distribution of charge collection, operando, is ascertained, and its application in colloidal quantum dot (CQD) solar cells is demonstrated at a wide range of relevant bias conditions. A systematic computational method that relies only on knowledge of measured optical parameters and bias-dependent external quantum efficiency spectra is implemented. It is found that, in CQD PV devices, the region near the thiol-treated hole-transport layer suffers from low collection efficiency, as a result of bad band alignment at this interface. The active layer is not fully depleted at short-circuit conditions, and this accounts for the limited short-circuit current of these CQD solar cells. The high collection efficiency outside of the depleted region agrees with a diffusion length on the order of hundreds of nanometers. The method provides a quantitative tool to study the operating principles and the physical origins of losses in CQD solar cells, and can be deployed in thin-film solar cell device architectures based on perovskites, organics, CQDs, and combinations of these materials.

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“…Hence, the suggested method has to be refined to accept arbitrary optical generation profiles. Pang et al 5 and Segev et al 9 suggested solving eqn (2) using standard regularization methods, such as Tichonov, 31,32 and applied it to CIGS solar cells 5 and hematite water splitting photoanodes, respectively. 9 In order to apply such methods, eqn (2) must be discretized:…”

Section: Discussionmentioning

confidence: 99%

“…The emergence of such a technique could significantly accelerate device and material development by providing insights into how bulk transport, photocarrier recombination, and surface chemical reaction govern performance characteristics under real operating conditions. In this work, we show that simple experimental techniques can be used to extract the spatial collection efficiency, [3][4][5][6][7][8][9] f(z), thereby allowing different loss mechanisms in an emerging semiconductor photoanode material, g-Cu 3 V 2 O 8 , to be probed and quantified. Defined as the fraction of optically generated charge carriers at a given location that contribute to the chemical reaction, the spatial collection efficiency (SCE) provides a functional depth profile of the active regions in the device.…”

Section: Introductionmentioning

confidence: 99%

“…Extraction of the SCE offers a non-destructive, operando method to evaluate and quantify the transport and loss mechanisms in new materials. [3][4][5][6][7][8][9] The method couples optical modelling based on data obtained from spectroscopic ellipsometry with incident photon-to-current efficiency (IPCE) measurements. As a recently discovered material system for water splitting, copper vanadate [25][26][27][28] serves as an excellent case study for the suggested method.…”

Section: Introductionmentioning

confidence: 99%

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Quantification of the loss mechanisms in emerging water splitting photoanodes through empirical extraction of the spatial charge collection efficiency

Segev

Jiang

Cooper

et al. 2018

Energy Environ. Sci.

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The operando quantification of surface and bulk losses is key to developing strategies for optimizing photoelectrodes and realizing high efficiency photoelectrochemical solar energy conversion systems. This is particularly true for emerging thin film semiconductors, in which photocarrier diffusion lengths, surface and bulk recombination processes, and charge separation and extraction limitations are poorly understood. Insights into mechanisms of efficiency loss can guide strategies for nanostructuring photoelectrodes, engineering interfaces, and incorporating catalysts. However, few experimental methods are available for direct characterization of dominant loss processes under photoelectrochemical operating conditions. In this work, we provide insight into the function and limitations of an emerging semiconductor photoanode, g-Cu 3 V 2 O 8 , by quantifying the spatial collection efficiency (SCE), which is defined as the fraction of photogenerated charge carriers at each point below the surface that contributes to the measured current. Analyzing SCE profiles at different operating potentials shows that increasing the applied potential primarily acts to reduce surface recombination rather than to increase the thickness of the space charge region under the semiconductor/ electrolyte interface. Comparing SCE profiles obtained with and without a sacrificial reagent allows surface losses from electronically active defect states to be distinguished from performance bottlenecks arising from slow reaction kinetics. Combining these insights promotes a complete understanding of the photoanode performance and its potential as a water splitting photoanode. More generally, application of the SCE extraction method can aid in the discovery and evaluation of new materials for solar water splitting devices by providing mechanistic details underlying photocurrent generation and loss. Broader contextThe next generation of solar energy conversion systems require design and integration of new semiconductor materials. Detailed understanding of the optoelectronic properties of these materials and the driving forces and loss mechanisms that limit device performance is essential to the development of high efficiency systems. Insights into mechanisms of efficiency loss can guide strategies for nanostructuring photoelectrodes, engineering interfaces, and incorporating catalysts. However, few experimental methods are available for direct characterization of dominant loss processes under photoelectrochemical operating conditions. In this work, we provide insight into the function and limitations of an emerging semiconductor photoanode, g-Cu 3 V 2 O 8 , by quantifying the spatial collection efficiency (SCE), which is defined as the fraction of photogenerated charge carriers at every point that contribute to extracted current. Analyzing SCE profiles at different operating potentials while performing different chemical reactions allows distinguishing between bulk and surface losses and between different types of surface recombination mechanisms...

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The Spatial Collection Efficiency of Charge Carriers in Photovoltaic and Photoelectrochemical Cells

Cited by 43 publications

References 59 publications

Film Flip and Transfer Process to Enhance Light Harvesting in Ultrathin Absorber Films on Specular Back‐Reflectors

Film Flip and Transfer Process to Enhance Light Harvesting in Ultrathin Absorber Films on Specular Back‐Reflectors

Spatial Collection in Colloidal Quantum Dot Solar Cells

Quantification of the loss mechanisms in emerging water splitting photoanodes through empirical extraction of the spatial charge collection efficiency

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