Quantifying Recombination Losses during Charge Extraction in Bulk Heterojunction Solar Cells Using a Modified Charge Extraction Technique

Wright, Brendan; Nakajima, Yukihiro; Clarke, Tracey M.; Okuda, Kouichi; Paananen, Heikki; Mozer, Attila J.; Mori, Shogo

doi:10.1002/aenm.201602026

Cited by 12 publications

(15 citation statements)

References 20 publications

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“…In fact, the exciton separation is typically accompanied with the charge recombination, which aggravates with enhanced n . [ 17 ] In this case, increasing electric field and the light intensity leads to higher electron concentration and enhanced charge recombination. Hence, we propose that the electric field, screening effect, and charge recombination on photoinduced charges are connected with the coupled modulation of σ.…”

Section: Figurementioning

confidence: 99%

Enhanced Thermoelectric Performance of n‐Type Organic Semiconductor via Electric Field Modulated Photo‐Thermoelectric Effect

et al. 2020

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Modulating photophysical processes is a fundamental way for tuning performance of many organic devices. However, it has not been explored as an effective strategy to manipulate the thermoelectric (TE) conversion of organic semiconductors (OSCs) owing to their critical requirement to carrier concentration (>1018 cm−3) and the fact of low exciton separation efficiency in single element OSCs. Here, an electric field modulated photo‐thermoelectric (P‐TE) effect in an n‐type OSC is demonstrated to realize a significant improvement of TE performance. The electrical and spectroscopy characterizations reveal that the electric field gating generates combined modulation of exciton separation, charge screening, and carrier recombination, which produces a more than ten times improvement of photoinduced carrier concentration. These coupled processes contribute to the unconventional Seebeck coefficient (S)‐electrical conductivity (σ) trade‐off relationship of the photoexcited films, therefore leading to a more than 500% enhancement in the power factor for n‐type OTE semiconductors. This work opens a unique way toward state‐of‐the‐art organic P‐TE materials for energy harvesting applications.

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Section: Figurementioning

confidence: 99%

Enhanced Thermoelectric Performance of n‐Type Organic Semiconductor via Electric Field Modulated Photo‐Thermoelectric Effect

et al. 2020

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“…where d is the device thickness, q is the unit charge, t e is the extraction time (usually 1 ms is enough), j ( t ) is the transient current density, C geom is the geometric capacitance, V a the voltage applied prior extraction (in most cases V oc ) and V e is the extraction voltage. The charge on the capacitance needs to be subtracted [ 83 ] because only the charge carrier density inside the bulk is of interest.…”

Section: Characterization Techniquesmentioning

confidence: 99%

Opto-electronic characterization of third-generation solar cells

Neukom

Züfle

Jenatsch

et al. 2018

Science and Technology of Advanced Materials

113

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We present an overview of opto-electronic characterization techniques for solar cells including light-induced charge extraction by linearly increasing voltage, impedance spectroscopy, transient photovoltage, charge extraction and more. Guidelines for the interpretation of experimental results are derived based on charge drift-diffusion simulations of solar cells with common performance limitations. It is investigated how nonidealities like charge injection barriers, traps and low mobilities among others manifest themselves in each of the studied cell characterization techniques. Moreover, comprehensive parameter extraction for an organic bulk-heterojunction solar cell comprising PCDTBT:PC70BM is demonstrated. The simulations reproduce measured results of 9 different experimental techniques. Parameter correlation is minimized due to the combination of various techniques. Thereby a route to comprehensive and accurate parameter extraction is identified.

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“…Instead of the surface passivation mechanism discussed above, the reduced recombination using PEDOT-PSS / and various electron interfacial layers is suggested to originate from the spatial charge separation of electrons and holes near the contacts, induced by the increased built-in electric field. Previous applied-bias and active layer thickness dependent charge extraction measurements suggested a similar mechanism 49. Charge carrier lifetimes in devices with thinner active layers were longer.…”

mentioning

confidence: 63%

“…Note that the photovoltage decay measurements were recorded using a 1 MOhm impedance, set by an oscilloscope.Therefore the decays measured towards the millisecond timescale could be influenced by current through the RC circuit, rather than recombination internally in the device. Therefore the measured curves are compared from the sub-microsecond to 1 ms time scale 49. The much higher transient photovoltage values for the reference device A compared to the steady state measurements (0.26 V) suggest higher charge density, at least initially, in transient measurements compared to what is achievable under AM 1.5 illumination.…”

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confidence: 99%

Effects of Interfacial Layers on the Open Circuit Voltage of Polymer/Fullerene Bulk Heterojunction Devices Studied by Charge Extraction Techniques

Saekung

Wright

Clarke

et al. 2019

ACS Appl. Mater. Interfaces

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Interfacial layers are frequently used in organic solar cells performing various functions, including blocking surface recombination, improving selectivity of charge carrier extraction, modification of the work function of the contact materials and enhancing light absorption within the photoactive layer through an optical cavity effect. The aim of this work is to investigate the origin of performance enhancement of bulk heterojunction solar cells using various electron and hole interfacial layers with a particular focus on the improvement to the open circuit voltage (Voc). Solar cells using poly[N-9′-hepta-decanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′benzothiadiazole)](PCDTBT) :)]:[6,6]-phenyl C70-butyric acid methyl ester (PC[70]BM) (1:4) active layers were prepared with a combination of polymeric, metal oxide and polyelectrolyte electron and or hole interfacial layers. Four device structures with i) no interfacial layers (reference); ii) only hole; iii) only electron; iv) both electron and hole interfacial layers were fabricated and compared using current-voltage, transient photovoltage and charge extraction measurements. The voltage gains (ΔVoc) at matched charge density due to work function modification (ΔVoc h or ΔVoc e) is distinguished from the increase in Voc due to increased charge carrier density due to longer charge carrier lifetime. At the hole contact, ΔVoc h was 0.21 V by using a PEDOT-PSS hole interfacial layer, while ΔVoc e was 0.29 V on the electron contact using a PEI-TiOx interfacial layer compared to reference devices. The electron lifetime also improved by orders of magnitude with the use of either electron or hole contact layers, contributing to a further 0.35-0.38 V increase in the open circuit voltage ((ΔVoc rec) due to increased charge density. The increased charge carrier lifetime is proposed to originate from the larger spatial separation of the electrons and holes in the device due to the increased internal field. Using both an electron and a hole interfacial layer didn't significantly increase the charge carrier lifetime compared to single interfacial layer devices, therefore the Voc didn't increase significantly. The findings presented clarify the role of interfacial layers in organic solar cells, and provides new insights into using time resolved charge extraction techniques to understand the influence of interfacial layers on the open circuit voltage.

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Quantifying Recombination Losses during Charge Extraction in Bulk Heterojunction Solar Cells Using a Modified Charge Extraction Technique

Cited by 12 publications

References 20 publications

Enhanced Thermoelectric Performance of n‐Type Organic Semiconductor via Electric Field Modulated Photo‐Thermoelectric Effect

Enhanced Thermoelectric Performance of n‐Type Organic Semiconductor via Electric Field Modulated Photo‐Thermoelectric Effect

Opto-electronic characterization of third-generation solar cells

Effects of Interfacial Layers on the Open Circuit Voltage of Polymer/Fullerene Bulk Heterojunction Devices Studied by Charge Extraction Techniques

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