Dielectric Effect on the Photovoltage Loss in Organic Photovoltaic Cells

Chen, Song; Tsang, Sai‐Wing; Lai, Tzung-Han; Reynolds, John R.; So, Franky

doi:10.1002/adma.201401987

Cited by 100 publications

(98 citation statements)

References 39 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…0.2 eV (−IP D and −EA A values shown in Fig. 1d), which were much less than empirical value 0.3−0.5 eV reported3940. The low V oc loss were attributed to their high dielectric constant (Supplementary Fig.…”

Section: Resultsmentioning

confidence: 72%

See 1 more Smart Citation

Fluorination-enabled optimal morphology leads to over 11% efficiency for inverted small-molecule organic solar cells

et al. 2016

View full text Add to dashboard Cite

Solution-processable small molecules for organic solar cells have attracted intense attention for their advantages of definite molecular structures compared with their polymer counterparts. However, the device efficiencies based on small molecules are still lower than those of polymers, especially for inverted devices, the highest efficiency of which is <9%. Here we report three novel solution-processable small molecules, which contain π-bridges with gradient-decreased electron density and end acceptors substituted with various fluorine atoms (0F, 1F and 2F, respectively). Fluorination leads to an optimal active layer morphology, including an enhanced domain purity, the formation of hierarchical domain size and a directional vertical phase gradation. The optimal morphology balances charge separation and transfer, and facilitates charge collection. As a consequence, fluorinated molecules exhibit excellent inverted device performance, and an average power conversion efficiency of 11.08% is achieved for a two-fluorine atom substituted molecule.

show abstract

Section: Resultsmentioning

confidence: 72%

“…The high V oc was in good agreement with the IP D of their blends obtained by UPS. As calculated from the formula: (refs 39, 40), the V oc losses (Δ V ) based on all three small molecules were ca. 0.2 eV (−IP D and −EA A values shown in Fig.…”

Section: Resultsmentioning

confidence: 99%

Fluorination-enabled optimal morphology leads to over 11% efficiency for inverted small-molecule organic solar cells

et al. 2016

View full text Add to dashboard Cite

show abstract

“…The capacitance measurements were calibrated with short and open-circuit corrections to eliminate the parasitic effects. [ 23 ] PDS measurements were carried out using a standard setup consisting of 1 kW Xe arc lamp and a 1/4 m grating monochromator (Oriel) as the tunable light source. The pump beam was modulated by a mechanical chopper at 13 Hz.…”

Section: Methodsmentioning

confidence: 99%

Effect of Thermal Annealing on Charge Transfer States and Charge Trapping in PCDTBT:PC₇₀BM Solar Cells

Constantinou

Lai

Hsu

et al. 2015

Adv Elect Materials

Self Cite

View full text Add to dashboard Cite

an increase in dielectric constant, thermal annealing also has a positive impact on the effectiveness of the CT states. More effective CT states were shown to facilitate exciton dissociation and charge carrier generation. Even though the resulting photogenerated current in annealed devices is higher, a signifi cant decrease in the device fi ll factor (FF) was observed, resulting in an overall decrease in device power conversion effi ciency. We found that the decrease in FF is resulted from an increase in monomolecular recombination due to the formation of mid-gap states determined from photothermal defl ection spectroscopy (PDS).The current density-voltage ( J-V ) characteristics for PCDTBT:PC 70 BM devices with and without annealing are presented in Figure 1 a. As shown in the fi gure, annealing at 150 °C results in a decrease in the overall device performance as has previously been reported. [ 8 ] The decrease in device performance after annealing is caused primarily by a decrease in FF from 56% to 46%, whereas the short circuit current ( J sc ) and open circuit voltage ( V oc ) remain mostly unchanged. A summary of the device parameters is given in Table S1 (Supporting Information). Interestingly, under reverse bias the current output for the annealed PCDTBT:PC 70 BM device is slightly higher than for the as-prepared device.In order to determine whether the current output for the annealed PCDTBT:PC 70 BM device at higher reverse bias is due to an increase in free carrier generation, the external quantum effi ciencies (EQEs) were measured at 540 nm as a function of reverse bias. The wavelength chosen for these measurements corresponds to a regime where the EQEs are the same for both devices under short circuit conditions (Figure 1 b inset). Figure 1 b shows the EQE under reverse bias for both devices in the fi eldassisted dissociation voltage regime. It is expected that the EQEs for the two devices should saturate at high reverse bias voltages where the IQE is approaching100%. [ 9 ] It is apparent from Figure 1 b that the carrier generation rate is higher for the annealed PCDTBT:PC 70 BM device and there are overall more available carriers to be collected compared to the device that was not annealed. The higher EQE at high reverse bias for the annealed device is in agreement with our J-V data confi rming that the charge generation rate is higher for the annealed devices. Even though the difference in performance observed under reverse bias is relatively small, it was consistently observed during the measurement of over 50 devices and has previously been observed in the literature. [ 10 ] We believe that this increase in charge generation after annealing is an indication of the formation of more effective CT states after thermal annealing.In order to confi rm that the increase in charge generation after annealing is not due to a dramatic change in the morphology of the blend, we examined the effects of thermal annealing on the morphological properties of the photoactive Thermal annealing has been commonly used i...

show abstract

“…OPV device is of much recent interest as a low-cost and lightweight renewable energy conversion technology [1][2][3]. Despite recent advances made in enhancement of power conversion efficiencies (PCE), much improvement on device lifetime and operational stabilities are still needed before wide commercial applications [4,5].…”

Section: Introductionmentioning

confidence: 99%

Degradation of interface between boron subphthalocyanine chloride and fullerene

Guan

Chan

et al. 2015

Journal of Electron Spectroscopy and Related Phenomena

View full text Add to dashboard Cite

Dielectric Effect on the Photovoltage Loss in Organic Photovoltaic Cells

Abstract: The VOC loss in several polymer-fullerene solar cells is determined. Based on these data, a major source of photovoltage loss is attributed to the low dielectric constants of the polymers. Such loss is close to zero if the dielectric constant of the polymer-fullerene blend is close to 5.

Cited by 100 publications

References 39 publications

Fluorination-enabled optimal morphology leads to over 11% efficiency for inverted small-molecule organic solar cells

Fluorination-enabled optimal morphology leads to over 11% efficiency for inverted small-molecule organic solar cells

Effect of Thermal Annealing on Charge Transfer States and Charge Trapping in PCDTBT:PC₇₀BM Solar Cells

Degradation of interface between boron subphthalocyanine chloride and fullerene

Contact Info

Product

Resources

About

Dielectric Effect on the Photovoltage Loss in Organic Photovoltaic Cells

Abstract: The VOC loss in several polymer-fullerene solar cells is determined. Based on these data, a major source of photovoltage loss is attributed to the low dielectric constants of the polymers. Such loss is close to zero if the dielectric constant of the polymer-fullerene blend is close to 5.

Cited by 100 publications

References 39 publications

Fluorination-enabled optimal morphology leads to over 11% efficiency for inverted small-molecule organic solar cells

Fluorination-enabled optimal morphology leads to over 11% efficiency for inverted small-molecule organic solar cells

Effect of Thermal Annealing on Charge Transfer States and Charge Trapping in PCDTBT:PC70BM Solar Cells

Degradation of interface between boron subphthalocyanine chloride and fullerene

Contact Info

Product

Resources

About

Effect of Thermal Annealing on Charge Transfer States and Charge Trapping in PCDTBT:PC₇₀BM Solar Cells