Life on the Urbach Edge

Ugur, Esma; Ledinský, Martin; Allen, Thomas G.; Holovský, Jakub; Vlk, Aleš; Wolf, Stefaan De

doi:10.1021/acs.jpclett.2c01812

Cited by 79 publications

(92 citation statements)

References 74 publications

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“…in which very few tail states ( E U < k B T ) below the bandgap are generally observed. − It is evident that the radiative loss occurs due to the tail state absorption of the photoactive layer, which can be minimized with a proper combination of D–A systems. Our observation shows good agreement with the expected relationship of V OC with E U . , A recent study also suggested that reducing the molecular vibration can lead to reduction in radiative voltage losses . Therefore, the fine-tuning of the molecular structure effectively regulates the molecular packing behavior, and it consequently plays an important role in reducing the energetic disorder and hence lower radiative recombination loss.…”

Section: Resultssupporting

confidence: 89%

“…Our observation shows good agreement with the expected relationship of V OC with E U . 64,65 A recent study also suggested that reducing the molecular vibration can lead to reduction in radiative voltage losses. 66 Therefore, the finetuning of the molecular structure effectively regulates the molecular packing behavior, and it consequently plays an important role in reducing the energetic disorder and hence lower radiative recombination loss.…”

Section: Donor−acceptor Systems With Different Energymentioning

confidence: 99%

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Role of Exciton Lifetime, Energetic Offsets, and Disorder in Voltage Loss of Bulk Heterojunction Organic Solar Cells

Suthar

Abhijith

Dahiya

et al. 2023

ACS Appl. Mater. Interfaces

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Recently, the power conversion efficiency (PCE) of organic solar cells (OSCs) has significantly progressed with a rapid increase from 10 to 19% due to state-of-theart research on nonfullerene acceptor molecules and various device processing strategies. However, OSCs still exhibit significant open circuit voltage loss (ΔV OC ∼ 0.6 V) due to high energetic offsets and molecular disorder. In this work, we present a systematic investigation to determine the effects of energetic offset and disorder on different recombination losses in open circuit voltage (V OC ) using 13 different photoactive layers, wherein the PCE and ΔV OC vary in the ranges of 2.21−14.74% and 0.561−1.443 V, respectively. The detailed voltage loss analysis of all these devices was carried out, and voltage losses were correlated with energetic offset and disorder. This has enabled us to identify the key features for minimizing the voltage loss like: (1) a low energy offset between the donor and acceptor molecular states is essential to attain a nonradiative voltage loss (ΔV OC, nrad ) as low as ∼200 meV and (2) Urbach energy, which is a measure of the materials' disorder and packing, should be low for the minimization of the radiative voltage loss (ΔV OC, rad ). In addition, time-resolved photoluminescence spectroscopy was employed to further understand the exciton dynamics of pristine materials and donor−acceptor blends. It was observed that the absorbers with ultralong exciton lifetime (∼1000 ps) produce higher efficiencies. The current study emphasizes the importance of simultaneously testing photovoltaic performance and active layer exciton dynamics for rational device optimization and opens new prospects for designing novel molecules with fine-tuning of energetic offset and disorder with longer exciton lifetime which is the effective strategy to boost the efficiency of OSCs to their modified Shockley−Queisser (SQ) limit by minimizing radiative and nonradiative voltage losses.

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Section: Resultssupporting

confidence: 89%

Section: Donor−acceptor Systems With Different Energymentioning

confidence: 99%

Role of Exciton Lifetime, Energetic Offsets, and Disorder in Voltage Loss of Bulk Heterojunction Organic Solar Cells

Suthar

Abhijith

Dahiya

et al. 2023

ACS Appl. Mater. Interfaces

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“…The Urbach energy has been shown to change with halide composition in systems such as MAPb(Br 1– x I x ) 3 . This band tailing in the density of states and the absorption spectra reduces the radiative efficiency of solar cells below the Shockley–Queisser limit by deviating from the step-function absorption assumption. − …”

mentioning

confidence: 99%

The Electronic Disorder Landscape of Mixed Halide Perovskites

et al. 2022

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Band gap tunability of lead mixed halide perovskites makes them promising candidates for various applications in optoelectronics. Here we use the localization landscape theory to reveal that the static disorder due to iodide:bromide compositional alloying contributes at most 3 meV to the Urbach energy. Our modeling reveals that the reason for this small contribution is due to the small effective masses in perovskites, resulting in a natural length scale of around 20 nm for the “effective confining potential” for electrons and holes, with short-range potential fluctuations smoothed out. The increase in Urbach energy across the compositional range agrees well with our optical absorption measurements. We model systems of sizes up to 80 nm in three dimensions, allowing us to accurately reproduce the experimentally observed absorption spectra of perovskites with halide segregation. Our results suggest that we should look beyond static contribution and focus on the dynamic temperature dependent contribution to the Urbach energy.

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Section: Resultsmentioning

confidence: 99%

“…Upon fitting this tail, we find that its Urbach energy is as high as 416 meV, indicating a strong energetic disorder that might be correlated with the amorphous arrangement of the lead halide frameworks (Figure S9b). 51,52 The PL properties of the products were investigated in detail. Under UV-light excitation, D230−Pb−Cl exhibits bright photoluminescence (PL), which emits blue light under 365 nm and blue-green light under 280 nm (Figure S10a−c).…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Noncrystalline Hybrid Lead Halides with Liquid-Polymer Characteristics

et al. 2022

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Hybrid lead halide (HLH) semiconductors, particularly those featuring perovskite and its derivative structures, have been popular materials with many promising optoelectronic applications. In general, HLHs are predominantly crystalline solids, whether they are bulk single crystals, microcrystals, or nanocrystals. This paper shows that when some short-chain Jeffamine, a widely used polyetheramine, is used as the organic species, the resultant HLH would become noncrystalline with unusual liquid-polymer-like characteristics. In this material, Jeffamine ammoniums and lead halide octahedron frameworks are both arranged amorphously, while its optical properties are similar to those of crystalline HLHs. In contrast to conventional organic species, Jeffamine exhibits a disordered molecular packing, which is believed to account for the peculiar characteristics of the HLH products. Through A-site engineering with Jeffamine, even classic lead halide perovskites such as CsPbBr3 can acquire partial noncrystallinity and transform into a liquid-polymer-like form. This discovery demonstrates that Jeffamine as a novel organic species would confer liquid-polymer properties to the products, which may provide a strategy to transform HLH materials and classic halide perovskites into special “liquid semiconductors”, thereby potentially enabling new processing techniques and new designs of soft electronics.

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Life on the Urbach Edge

Cited by 79 publications

References 74 publications

Role of Exciton Lifetime, Energetic Offsets, and Disorder in Voltage Loss of Bulk Heterojunction Organic Solar Cells

Role of Exciton Lifetime, Energetic Offsets, and Disorder in Voltage Loss of Bulk Heterojunction Organic Solar Cells

The Electronic Disorder Landscape of Mixed Halide Perovskites

Noncrystalline Hybrid Lead Halides with Liquid-Polymer Characteristics

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