Structural Order: The Dominant Factor for Nongeminate Recombination in Organic Photovoltaic Devices

Xu, Liang; Wang, Jian; Hsu, Julia W. P.

doi:10.1021/acs.jpcc.7b03183

Cited by 3 publications

(4 citation statements)

References 47 publications

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“…Bimolecular (non-geminate) recombination of the electrons and holes in the CS state is expected to occur in microseconds as reported for similar PSC systems. [64,65] For the bleach band of the donor (XB D ), we observed a minor bleach that was built on an approximately 20 ps timescale. The hole transfer from the HOMO of an acceptor, which can also be photoexcited at The aforementioned absorption bands are all superimposed across the monitored wavelengths.…”

Section: Resultsmentioning

confidence: 83%

Viable Mixing Protocol Based on Formulated Equations for Achieving Desired Molecular Weight and Maximal Charge Separation of Photovoltaic Polymer

Lee

Kim

Nho

et al. 2021

Advanced Energy Materials

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acceptors have garnered extensive interest due to their benefits of the simple device structure, lightweight, flexibility, and low manufacturing cost using printing technologies. [1][2][3][4] Rapid material development and device-engineering advancement in the BHJ PSC community has resulted in a major increase in PSC performance over the past few decades, culminating in substantial breakthroughs in power conversion efficiencies (PCEs), which now exceed 18%. [5][6][7] Despite the success of the field of PSCs, batch-to-batch differences in molecular weight of a conjugated polymer used as one of the active layer components within a BHJ active layer, led to inconsistency in macromolecular ordering, optoelectronic and charge transport characteristics, and ultimately device performance. [8][9][10][11] There have been several attempts to overcome the molecular weight limitations caused by synthetic polymers. For example, You's and Marks's groups independently demonstrated the possibility of controlling polymer's molecular weight via a synthetic strategy based on the classic Carothers equation, considering the comonomer ratios and degree of polymerization. [12,13] We recently established a successful stepwise polymerization methodology for synthesizing high-quality polymers with narrow polydispersity and high molecular weight. [14] McCulloch et al. also isolated polymer fractions with well-defined molecular weights and narrow polydispersity using reparative-scale recycling size exclusion chromatography (rec-SEC). [15] These findings are useful in improving batch-to-batch reproducibility. To execute these technologies successfully, the reactant monomers and palladium (Pd) catalysts must be rigorously purified via multiple purification technologies and precisely weighed to ensure proper stoichiometric balance; otherwise, fractionation via the rec-SEC equipment must be tailored to the polymers produced, making it difficult to use in large-scale production. Hence, such methods are commercially inefficient and nonproductive.In this study, effective mathematical equations capable of achieving polymer batches with controlled molecule weights have been formulated. A series of PM6 donor polymers with varying molecular weights was prepared at different reaction times to verify the equations' effectiveness. Polymers with A major difficulty in the polymer solar cell (PSC) community is discovering a methodology capable of accessing polymeric photovoltaic materials with controllable/predictable molecular weights. Effective mathematical equations that enable the reproduction of polymer batches with precisely controlled molecular weight, by mixing as-synthesized polymer batches with the ones that have different molecular weights, are formulated in this study. The properties of both the as-synthesized and mixed-different-molecular weight PM6 polymer series are systematically investigated to determine the effect of molecular weight on the performance of related PSCs. The power conversion efficiencies (PCEs) improve monotonically with an i...

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Section: Resultsmentioning

confidence: 83%

Viable Mixing Protocol Based on Formulated Equations for Achieving Desired Molecular Weight and Maximal Charge Separation of Photovoltaic Polymer

Lee

Kim

Nho

et al. 2021

Advanced Energy Materials

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“…Furthermore, for many fullerene acceptor systems, for example, P3HT:PC 71 BM, BHJ V oc is much lower than that for DD OPVs for the same donor−acceptor pair. 2,8,42 Thus, compared to BHJ, the V oc variation in DD OPVs seems to be negligible. By examining a wider variety of donors in fullerene and NFA acceptors, we show here that a low concentration of donors does affect V oc quite significantly, largely determined by nonradiative loss.…”

Section: Resultsmentioning

confidence: 93%

“…For donor materials with similar structures or chemistry, they will interact similarly with the acceptor, leading to comparable charge recombination rates and non-radiative voltage loss; therefore, V oc values would appear independent of donors. Furthermore, for many fullerene acceptor systems, for example, P3HT:PC 71 BM, BHJ V oc is much lower than that for DD OPVs for the same donor–acceptor pair. ,, Thus, compared to BHJ, the V oc variation in DD OPVs seems to be negligible. By examining a wider variety of donors in fullerene and NFA acceptors, we show here that a low concentration of donors does affect V oc quite significantly, largely determined by non-radiative loss.…”

Section: Resultsmentioning

confidence: 96%

Re-Examining Open-Circuit Voltage in Dilute-Donor Organic Photovoltaics

et al. 2022

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Dilute-donor (DD) organic photovoltaic (OPV) devices comprise a low concentration of donor molecules in an acceptor matrix. The open-circuit voltage (V oc) of these devices is commonly higher than their bulk heterojunction (BHJ) counterparts and has been attributed to Schottky barrier heights between the anode and the acceptor matrix or reduced bimolecular recombination due to smaller donor/acceptor interfacial areas. Here, we examine the V oc of a variety of small-molecule and polymer donors, all at 5 wt %, in both fullerene and non-fullerene acceptors by performing photovoltaic (PV) and electroluminescence (EL) measurements on the same devices. We find a substantial V oc variation for different donors in the same acceptor matrix, indicating that DD V oc cannot be adequately explained by the Schottky barrier or interfacial area. V oc values of fullerene DD devices vary linearly with the band gap value as determined from the intercept of PV external quantum efficiency and EL spectra. In contrast, the non-fullerene acceptor (NFA) DD devices show V oc variation with donors despite having the same band gap. These results show that V oc of DD OPVs is predominantly determined by non-radiative voltage loss, similar to BHJ OPVs. NFA-based DD devices show promises for low voltage loss and high charge generation.

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“…Nesse sentido, inúmeros trabalhos [45][46][47] 34 Obviamente, a morfologia das heterojunções (doador-aceitador) tem um papel crucial sobre os eventos de recombinação. [50][51]…”

Section: Recombinaçãounclassified

Análise teórico-experimental sobre mecanismos de transporte em células solares orgânicas de P3HT e PCBM

Amorim¹

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Structural Order: The Dominant Factor for Nongeminate Recombination in Organic Photovoltaic Devices

Cited by 3 publications

References 47 publications

Viable Mixing Protocol Based on Formulated Equations for Achieving Desired Molecular Weight and Maximal Charge Separation of Photovoltaic Polymer

Viable Mixing Protocol Based on Formulated Equations for Achieving Desired Molecular Weight and Maximal Charge Separation of Photovoltaic Polymer

Re-Examining Open-Circuit Voltage in Dilute-Donor Organic Photovoltaics

Análise teórico-experimental sobre mecanismos de transporte em células solares orgânicas de P3HT e PCBM

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