Direct observation of trap-assisted recombination in organic photovoltaic devices

Zeiske, Stefan; Sandberg, Oskar J.; Zarrabi, Nasim; Li, Wei; Meredith, Paul; Armin, Ardalan

doi:10.1038/s41467-021-23870-x

Cited by 93 publications

(85 citation statements)

References 41 publications

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“…Furthermore, this work solely focuses on the trap at the shallow tail states rather than the midgap trap states. Recent research has proposed that the recombination from the trap state located 0.35–0.6 eV below the transport edges can be switched off at low incident light intensities . Further efforts are required to separate and clarify the effects from different types of trap states to assist future research in the indoor OPV community.…”

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confidence: 99%

Trap State Induced Recombination Effects on Indoor Organic Photovoltaic Cells

et al. 2021

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Organic photovoltaic (OPV) cells have shown effectiveness as off-grid power entities to drive the low power consumption electronics among the Internet of Things. The trap states and the induced recombination in OPV cells are critically relevant to the photovoltaic performance but remain ambiguous in OPV cells for indoor application. Here, we investigate the trap effects on the indoor photovoltaic performance by employing PBBD-T series donors and wide bandgap acceptor BTA3. It is revealed that the discrete density of state in OPV cells introduces low-lying trap states and further aggravates the trap-induced recombination. Instead of the domination of bimolecular recombination under solar radiation, trap-induced recombination prevails under indoor scenarios because of the low level of carrier densities under indoor weak illuminations. This work illustrates the details of charge carrier recombination behavior in OPV cells for indoor application and points out the importance of trap controlling in achieving high-performance indoor OPV cells.

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confidence: 99%

Trap State Induced Recombination Effects on Indoor Organic Photovoltaic Cells

et al. 2021

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“…The relationships of V oc and P light of the two blends are presented in Figure 3f. 45,46 The slope values were calculated to be 1.15 kT/q for the PBDB-T:QOC6-4Cl blend and 1.28 kT/q for the PBDB-T:QOC6-4H blend, indicating that the QOC6-4H blend suffers more severe trap-assisted recombination than QOC6-4Cl-based blend. The J sc vs P light curves of the QOC6-4X-based device are shown in Figure S8a.…”

Section: T H Imentioning

confidence: 99%

Facile Modification of a Noncovalently Fused-Ring Electron Acceptor Enables Efficient Organic Solar Cells

Huang

Qin

et al. 2021

ACS Appl. Mater. Interfaces

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Electron acceptors with nonfused aromatic cores (NCAs) have aroused increasing interest in organic solar cells due to the low synthetic complexity and flexible chemical modification, but the corresponding device performance still lags behind. Herein, we designed and synthesized two new quinoxaline-based NCAs, namely, QOC6-4H and QOC6-4Cl. Although both NCAs show good backbone coplanarity, QOC6-4Cl with chlorinated end groups exhibits higher extinction coefficient, enhanced crystallinity, and more compact π−π stacking, which is correlated with the stronger intermolecular interactions induced by chlorine atoms. Benefiting from the broader and stronger optical absorption, improved carrier mobilities, and suppressed charge recombination, a notable power conversion efficiency (PCE) of 12.32% with a distinctly higher short-current density (J sc ) of 22.91 mA cm −2 and a fill factor (FF) of 69.01% could be obtained for the PBDB-T:QOC6-4Cl-based device. The PCEs of PBDB-T:QOC6-4H were only lower than 8%, which could mainly be attributed to the unsymmetric charge transport. Our work proves that the chlorination of end groups is a facile and effective strategy to enhance the intermolecular interactions and thus the photovoltaic performance of NCAs, and a careful modulation of the intermolecular interactions plays a vital role in further developing both high-performance and low-cost organic photovoltaic materials.

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“…In organic semiconductors, the presence of trap states has been previously shown via sensitively measured photothermal deflection spectroscopy as well as intensity dependent photocurrent measurements for a large set of fullerene and non-fullerene blends. 18 Recently, the effect of mid-gap trap states has also been observed in the sub-gap EQE 19 directly and by impedance spectroscopy. 20 In this work, we provide evidence that the dark saturation current in organic photodiodes is dominated by recombination via mid-gap trap states.…”

Section: Introductionmentioning

confidence: 99%

Mid-gap Trap State Mediated Dark Current in Organic Photodiodes

Kaiser

Sandberg

Zeiske

et al. 2021

Preprint

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Photodiodes are ubiquitous in industry and consumer electronics. New applications for photodiodes are constantly emerging, such as the internet of things and wearable electronics that demand different mechanical and optoelectronic properties from those provided by conventional inorganic devices. This has stimulated considerable interest in the use of next generation semiconductors, particularly the organics, which provide a vast palette of available optoelectronic properties, can be incorporated into flexible form factor geometries, and promise extremely low cost, low embodied energy manufacturing from earth abundant materials. The sensitivity of a photodiode to low light intensities (typically important in these new applications) depends critically on the dark current. Organic photodiodes, however, are characterized by a much higher dark current than expected for thermally excited band-to-band transitions. Here, we show that the lower limit of the dark current is given by recombination via mid-gap trap states. This new insight is generated from temperature dependent dark current measurements of narrow-gap photodiodes for the near-infrared. Based on Shockley-Read-Hall statistics, a diode equation is derived which can be used to determine an upper limit for the specific detectivity and to explain the general trend observed for the light to dark current ratio as a function of the experimental open-circuit voltage for a series of organic photodiodes. A detailed understanding of the origins of noise in any detector is fundamental to defining performance limitations and thus is critical to materials and device selection, design and optimisation for all applications. Our work establishes these important principles for organic semiconductor photodiodes for the near-infrared.

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Direct observation of trap-assisted recombination in organic photovoltaic devices

Cited by 93 publications

References 41 publications

Trap State Induced Recombination Effects on Indoor Organic Photovoltaic Cells

Trap State Induced Recombination Effects on Indoor Organic Photovoltaic Cells

Facile Modification of a Noncovalently Fused-Ring Electron Acceptor Enables Efficient Organic Solar Cells

Mid-gap Trap State Mediated Dark Current in Organic Photodiodes

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