Highly efficient organic solar cells based on a poly(2,7-carbazole) derivative

Wakim, Salem; Beaupré, Serge; Blouin, Nicolas; Aich, Badrou-Réda; Rodman, Sheila; Gaudiana, Russell; Tao, Ye; Leclerc, Mario

doi:10.1039/b901302d

Cited by 187 publications

(146 citation statements)

References 38 publications

Supporting

Mentioning

137

Contrasting

Order By: Relevance

“…It is thus not surprising that typically BHJ OPVs with a polymer/PC 70 BM active layer show improved performance than the OPVs with polymer/PC 60 BM active layers. 7,17,18 By controlling the BTT-DPP/PC 70 BM composition ratio we were able to optimise the device power conversion efficiencies to a maximum of 3.1%. In addition, we have shown that device J SC is limited by the efficiency of the PC 70 BM exciton dissociation, attributed to the tendency of PCBM to form large, relatively pure domains with domain sizes longer than the PCBM exciton diffusion length.…”

mentioning

confidence: 99%

“…7 Low bandgap BHJ devices utilizing PC 70 BM as an electron acceptor have consistently performed better than the devices with the more common electron acceptor PC 60 BM. 7,[17][18] Although these two fullerene derivatives have similar ionisation potential (IP), electron affinity (EA) and sizes, the increase in device efficiencies when PC 70 BM is used has been attributed to its improved light absorption. 7,19 The increased light absorption of PC 70 BM relative to PC 60 BM has been attributed to its lower symmetry resulting in otherwise forbidden singlet transitions in PC 60 BM becoming allowed.…”

mentioning

confidence: 99%

See 1 more Smart Citation

Efficient Charge Photogeneration by the Dissociation of PC₇₀BM Excitons in Polymer/Fullerene Solar Cells

Dimitrov

Nielsen

Shoaee

et al. 2011

J. Phys. Chem. Lett.

View full text Add to dashboard Cite

ABSTRACT:The role of PC 70 BM excitons in driving charge photogeneration in low bandgap polymer/fullerene bulk heterojunction solar cells has been studied. Both transient absorption spectroscopy (TAS) of charge generation yields in blend films as a function of excitation energies and photocurrent quantum efficiency spectra of the corresponding devices indicate that charge generation in this system results primarily from direct optical excitation of PC 70 BM. Blend composition studies of photocurrent density and photoluminescence quenching indicate that the efficiency of photocurrent generation is primarily determined by the limited efficiency of PC 70 BM exciton diffusion to the polymer, due to the formation of PC 70 BM domains (≥ 5nm). This limitation becomes more severe as the PC 70 BM content is increased above 50%. Despite this limitation, and despite the poor charge photogeneration from polymer excitons, organic solar cells fabricated using this photoactive blend layer yielded device photocurrents of 7.1 mA/cm 2 , maximal EQE's of 41% and a device efficiency of 3.1%.The most efficient organic photovoltaic (OPV) devices are now reaching power conversion efficiencies of 8%.1-4 Their active layer consists of a bicontinuous network of a small bandgap polymer and a soluble fullerene that act as an electron donor and acceptor (D/A) pair.5 Charge photogeneration in these devices is typically considered to be initiated by photon absorption by the polymer followed by electron transfer from the polymer to the fullerene. 5,6 However increasing attention is being placed upon the role of the acceptor as an additional light absorbing element of the device, motivated in particular by the increased use of C 70 based acceptors such as [6,6]-phenyl-C71-butyric acid methyl ester (PC 70 BM) which exhibit significant visible light absorption. 7,8 Charge generation from fullerene excitons can proceed either by direct hole transfer from the fullerene to the polymer (sometimes referred to as reverse electron transfer), or by exciton energy transfer from the fullerene to the polymer followed by the conventional electron transfer from the polymer exciton to the fullerene.9-11 Neither of these charge separation pathways have received much attention to date compared to the more conventional charge generation pathway initiated by polymer light absorption in such blend films. Time-resolved spectroscopy experiments have estimated that hole transfer in polymer/PC 60 BM films is an ultrafast process with efficiencies limited by phase segragation in the blends. 9,10,12 In this letter we report our investigations on the contribution of photoinduced hole transfer to the device photocurrent for an OPV device with an active layer comprising a blend film of the small bandgap polymer BTT-DPP and PC 70 BM. By means of transient absorption spectroscopy we demonstrate that the BTT-DPP exciton is unable to drive efficient charge separation, with charge photogeneration in the device active layer resulting primarily from PC 70 BM light absorption, ...

show abstract

mentioning

confidence: 99%

mentioning

confidence: 99%

Efficient Charge Photogeneration by the Dissociation of PC₇₀BM Excitons in Polymer/Fullerene Solar Cells

Dimitrov

Nielsen

Shoaee

et al. 2011

J. Phys. Chem. Lett.

View full text Add to dashboard Cite

show abstract

“…The performance metrics including relevant statistics are summarized in Table 1. It has previously been demonstrated that the Fill Factor (FF) and PCE fall off rapidly for junctions > 80 nm for PCDTBT:PC70BM [133], and we also observe the same trend. This has been attributed to poor charge transport in this blend, in particular low hole mobilities which leads to significant bimolecular recombination under 1 sun operating conditions.…”

Section: Photovoltaic Performance Of Solar Cellssupporting

confidence: 68%

“…The structures of the two different polymers are provided Figure 1. These systems have been extensively studied [54,104,107,132,133] and are known to have quite different charge transport properties (PTB7:PC70BM being superior). In this work we varied the junction thickness as an experimental parameter so as to access a range of key charge transport properties (recombination and mobility) in a systematic manner and study their impact upon device performance.…”

Section: Photovoltaic Performance Of Solar Cellsmentioning

confidence: 99%

“…Both blends have been also extensively studied [54,107,132,133] and are known to have quite different charge transport properties (PTB7:PC70BM being superior). In order to elucidate the cause for dispersive transport we performed transient photoconductivity experiments in which we vary the transit time by changing the electric field and/or device thickness.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Charge Generation and Transport Phenomena in Disordered Organic Semiconductors and Photovoltaic Diodes

Stolterfoht¹

View full text Add to dashboard Cite

Organic semiconductors are of great interest for a broad range of optoelectronic applications due to their solution processability, chemical tunability and mechanical flexibility. In contrast to traditional banded semiconductors, organic semiconductors are intrinsically disordered systems and exhibit therefore much lower charge carrier mobilities. They are also low dielectric constant systems -as such, their photo-excitations are excitonic at room temperature with the electron-hole pair remaining Coulombically-bound. Blending organic semiconductors with differing electron affinities, so-called electron acceptors and donors, creates molecular heterojunctions which deliver the required driving force for exciton separation. These so-called bulk heterojunctions (BHJs) are the dominant architecture for creating organic photovoltaic cells and photodetectors. However, not least because of an incomplete understanding of the underlying physical mechanism that control the conversion of photons to free charges, and the subsequent extraction of these free charges to the electrodes, these organic optoelectronic systems still lag behind their inorganic counterparts.Motivated by these factors, the work described in this thesis advances the fundamental understanding of the loss mechanisms associated with charge photogeneration and charge transport phenomena in BHJ organic solar cells and photodetectors, and presents new experimental methodologies to study these processes. The transport of photogenerated charge carriers in the percolated donor: acceptor pathways towards the extracting electrodes has been studied in-depth via existing and newly developed transient photovoltage and steady-state characterization techniques. A simple but conclusive understanding has been developed which allows for minimization of the detrimental recombination of free charge carriers for given device parameters such as film thickness, applied voltage and the mobility of the slower carrier type (either electrons or holes). The models' predictions have been experimentally validated for many different (> 25) BHJ solar cell systems. Inspired by the need to selectively optimize the processes which control the photocurrent output of the cell, such a charge photogeneration and extraction, a technique to quantify and disentangle both efficiencies has been developed as a next step. Corroborated by transient absorption spectroscopy, the dynamics of the photocarrier generation process was examined. The results suggest that the so-called charge-transfer state (CTS) separation limits the conversion of photons to free charges and the photocurrent output from short-circuit to the maximum power point, strongly depending on the slower carrier ii mobility. These findings were explained by the ability of the slower carriers to leave the donor: acceptor interface via 1) a high enough mobility, 2) a sufficiently large domain size, and 3) enough conduction pathways (entropy). This work also shows that the dynamics of charge extraction and CTS dissociation are simi...

show abstract

Dithienocarbazole‐Based Ladder‐Type Heptacyclic Arenes with Silicon, Carbon, and Nitrogen Bridges: Synthesis, Molecular Properties, Field‐Effect Transistors, and Photovoltaic Applications

Wu¹,

Cheng²,

Lin³

et al. 2012

Adv Funct Materials

View full text Add to dashboard Cite

A new class of ladder‐type dithienosilolo‐carbazole (DTSC), dithienopyrrolo‐carbazole (DTPC), and dithienocyclopenta‐carbazole (DTCC) units is developed in which two outer thiophene subunits are covalently fastened to the central 2,7‐carbazole cores by silicon, nitrogen, and carbon bridges, respectively. The heptacyclic multifused monomers are polymerized with the benzothiadiazole (BT) acceptor by palladium‐catalyzed cross‐coupling to afford three alternating donor‐acceptor copolymers poly(dithienosilolo‐carbazole‐alt‐benzothiadiazole) (PDTSCBT), poly(dithienocyclopenta‐carbazole‐alt‐benzothiadiazole) (PDTCCBT), and poly(dithienopyrrolo‐carbazole‐alt‐benzothiadiazole) (PDTPCBT). The silole units in DTSC possess electron‐accepting ability that lowers the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of PDTSCBT, whereas stronger electron‐donating ability of the pyrrole moiety in DTPC increases the HOMO and LUMO energy levels of PDTPCBT. The optical bandgaps (Egopt) deduced from the absorption edges of thin film spectra are in the following order: PDTSCBT (1.83 eV) > PDTCCBT (1.64 eV) > PDTPCBT (1.50 eV). This result indicated that the donor strength of the heptacyclic arenes is in the order: DTPC > DTCC > DTSC. The devices based on PDTSCBT and PDTCCBT exhibited high hole mobilities of 0.073 and 0.110 cm2 V−1 s−1, respectively, which are among the highest performance from the OFET devices based on the amorphous donor‐acceptor copolymers. The bulk heterojunction photovoltaic device using PDTSCBT as the p‐type material delivered a promising efficiency of 5.2% with an enhanced open circuit voltage, Voc, of 0.82 V.

show abstract

Highly efficient organic solar cells based on a poly(2,7-carbazole) derivative

Cited by 187 publications

References 38 publications

Efficient Charge Photogeneration by the Dissociation of PC₇₀BM Excitons in Polymer/Fullerene Solar Cells

Efficient Charge Photogeneration by the Dissociation of PC₇₀BM Excitons in Polymer/Fullerene Solar Cells

Charge Generation and Transport Phenomena in Disordered Organic Semiconductors and Photovoltaic Diodes

Dithienocarbazole‐Based Ladder‐Type Heptacyclic Arenes with Silicon, Carbon, and Nitrogen Bridges: Synthesis, Molecular Properties, Field‐Effect Transistors, and Photovoltaic Applications

Contact Info

Product

Resources

About

Highly efficient organic solar cells based on a poly(2,7-carbazole) derivative

Cited by 187 publications

References 38 publications

Efficient Charge Photogeneration by the Dissociation of PC70BM Excitons in Polymer/Fullerene Solar Cells

Efficient Charge Photogeneration by the Dissociation of PC70BM Excitons in Polymer/Fullerene Solar Cells

Charge Generation and Transport Phenomena in Disordered Organic Semiconductors and Photovoltaic Diodes

Dithienocarbazole‐Based Ladder‐Type Heptacyclic Arenes with Silicon, Carbon, and Nitrogen Bridges: Synthesis, Molecular Properties, Field‐Effect Transistors, and Photovoltaic Applications

Contact Info

Product

Resources

About

Efficient Charge Photogeneration by the Dissociation of PC₇₀BM Excitons in Polymer/Fullerene Solar Cells

Efficient Charge Photogeneration by the Dissociation of PC₇₀BM Excitons in Polymer/Fullerene Solar Cells