Charge versus Energy Transfer Effects in High-Performance Perylene Diimide Photovoltaic Blend Films

Singh, Ranbir; Shivanna, Ravichandran; Iosifidis, Agathaggelos; Butt, Hans‐Jürgen; Floudas, George; Narayan, K. S.; Keivanidis, Panagiotis E.

doi:10.1021/acsami.5b08224

Cited by 28 publications

(29 citation statements)

References 66 publications

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“…We have also investigated the PL quenching efficiency of bis-PDI (excited at 532 nm), revealing almost complete quenching in the PffBT4T-2OD:bis-PDI blend films (Figure S3). The complete quenching of bis-PDI excimers implies that bis-PDI is relatively close to the polymer or bis-PDI domain sizes lying well within the excimer diffusion length, so bis-PDI excimers could reach a heterojunction before emitting 31,32 . The AFM images of these two systems are showed in Figure S4.…”

Section: Resultsmentioning

confidence: 99%

Unraveling the efficiency-limiting morphological issues of the perylene diimide-based non-fullerene organic solar cells

Singh

Suranagi

Lee

et al. 2018

Sci Rep

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Herein we report a comparative morphological analysis of the perylene diimide (PDI)- and fullerene-based organic solar cells (OSCs) to identify the factors responsible for low performance of PDI-based devices. A PDI derivative, bis-PDI, and a fullerene derivative, PC70BM, are mixed with an efficient polymer donor, PffBT4T-2OD. The large disparity in power conversion efficiencies (PCEs) of OSCs composed of PffBT4T-2OD:bis-PDI (PCE = 5.18%) and PffBT4T-2OD:PC70BM (PCE = 10.19%) observed are attributed to differences in the nanostructural motif of bulk heterojunction (BHJ) morphologies of these blend systems. The X-ray scattering and surface energy characterizations revealed that the structurally dissimilar bis-PDI and PC70BM molecules determine the variation in blend film morphologies, and in particular, the molecular packing features of the donor PffBT4T-2OD polymer. In addition, high-resolution transmission electron microscopy (HRTEM) images explore the BHJ morphologies and presence of longer polymer fibrils in PffBT4T-2OD:bis-PDI system, justifying the unbalanced charge transport and high hole mobility. The low performance of PffBT4T-2OD:bis-PDI devices was further investigated by studying charge carrier recombination dynamics by using light-intensity-dependent and transient photovoltage (TPV) experiments. Furthermore, the temperature-dependent experiments showed the photovoltaic properties, including charge recombination losses, are strongly affected by energetic disorder present in bis-PDI-based system.

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Section: Resultsmentioning

confidence: 99%

Unraveling the efficiency-limiting morphological issues of the perylene diimide-based non-fullerene organic solar cells

Singh

Suranagi

Lee

et al. 2018

Sci Rep

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“…A recent report by Singh et al has specifically looked at the question of energy transfer versus charge transfer processes in PDI:PBDTTT-CT blends ( Figure 9a). 91 Due to the overlap of the PDI photoluminescence with the polymer absorption, the conditions are present to allow for FRET from the PDI to the polymer (Figure 9b). The authors varied the blend ratio and found that there was inefficient quenching of the PDI excimer, even though a substantial amount of polymer was present (10 wt %).…”

Section: Categorizing Donor−acceptor Blends By Their Absorptionmentioning

confidence: 99%

Charge Generation Pathways in Organic Solar Cells: Assessing the Contribution from the Electron Acceptor

et al. 2016

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Photocurrent generation in organic bulk heterojunction (BHJ) solar cells is most commonly understood as a process which predominantly involves photoexcitation of the lower ionization potential species (donor) followed by electron transfer to the higher electron affinity material (acceptor) [i.e., photoinduced electron transfer (PET), which we term Channel I]. A mirror process also occurs in which photocurrent is generated through photoexcitation of the acceptor followed by hole transfer to the nonexcited donor or photoinduced hole transfer (PHT), which we term Channel II. The role of Channel II photocurrent generation has often been neglected due to overlap of the individual absorption spectra of the donor and acceptor materials that are commonly used. More recently Channel II charge generation has been explored for several reasons. First, many of the new high-efficiency polymeric donors are used as the minority component in bulk heterojunction blends, and therefore, the acceptor absorption is a significant fraction of the total; second, nonfullerene acceptors have been prepared, which through careful design, allow for spectral separation from the donor material, facilitating fundamental studies on charge generation. In this article, we review the methodologies for investigating the two charge generation channels. We also discuss the factors that affect charge generation via Channel I and II pathways, including energy levels of the materials involved, exciton diffusion, and other considerations. Finally, we take a comprehensive look at the nonfullerene acceptor literature and discuss what information about Channel I and Channel II can be obtained from the experiments conducted and what other experiments could be undertaken to provide further information about the operational efficiencies of Channels I and II.

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“…We mention here the similarities of the temperature location of the two phase transitions with another PDI-based blend system investigated earlier by some of us. 45 In addition to the location of phase transformations WAXS provides information on the PDI and polymer domains sizes as a function of temperature (extracted from the peak FWHM). The PDI domains are composed of stacks of PDI molecules in a columnar arrangement.…”

Section: Morphology and Structure Characterizationmentioning

confidence: 99%

Afterglow Effects as a Tool to Screen Emissive Nongeminate Charge Recombination Processes in Organic Photovoltaic Composites

Keivanidis

Itskos

Kan

et al. 2019

ACS Appl. Mater. Interfaces

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Disentangling temporally-overlapping charge carrier recombination events in organic bulk heterojunctions by optical spectroscopy is challenging. Here, a new methodology for employing delayed luminescence spectroscopy is presented. The proposed method is capable of distinguishing between recombination of spatially-separated charge carriers and trap-assisted charge recombination simply by monitoring the delayed luminescence (afterglow) of bulk heterojunctions with a quasi timeintegrated detection scheme. Applied on the model composite of the donor poly (6,12-dihydro-6,6,12,12-tetraoctyl-indeno[1,2-b]fluorene-alt-benzothiadiazole) (PIF8BT) polymer and the acceptor ethyl-propyl perylene diimide (PDI) derivative, i.e. PIF8BT:PDI, the luminescence of charge-transfer (CT) states created by non-geminate charge recombination on the ns -μs time scale is observed. Fluence-dependent, quasi time-integrated detection of the CT luminescence monitors exclusively emissive charge recombination events, while rejecting the contribution of other early-time emissive processes. Trap-assisted and bimolecular charge recombination channels are identified based on their distinct dependence on fluence. The importance of the two recombination channels is correlated with the layer's order and electrical properties of the corresponding devices. Four different microstructures of the PIF8BT:PDI composite obtained by thermal annealing are investigated. Thermal annealing of PIF8BT:PDI shrinks the PDI domains in parallel with the growth of the PIF8BT domains in the blend. Common to all states studied, the delayed CT luminescence signal is dominated by trap-assisted recombination. Yet, the minor fraction of fully-separated charge recombination in the overall CT emission increases as the difference in the size of the donor and acceptor domains in the PIF8BT:PDI blend becomes larger. Electric field-induced quenching measurements on complete PIF8BT:PDI devices confirm quantitatively the dominance of emissive trap-limited charge recombination and demonstrate that only 40% of the PIF8BT/PDI CT luminescence comes from the recombination of fully-separated charges, taking place within 200 ns after photoexcitation. The method is applicable to other non-fullerene acceptor blends beyond the system discussed here, if their CT state luminescence can be monitored.

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Charge versus Energy Transfer Effects in High-Performance Perylene Diimide Photovoltaic Blend Films

Cited by 28 publications

References 66 publications

Unraveling the efficiency-limiting morphological issues of the perylene diimide-based non-fullerene organic solar cells

Unraveling the efficiency-limiting morphological issues of the perylene diimide-based non-fullerene organic solar cells

Charge Generation Pathways in Organic Solar Cells: Assessing the Contribution from the Electron Acceptor

Afterglow Effects as a Tool to Screen Emissive Nongeminate Charge Recombination Processes in Organic Photovoltaic Composites

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