Temperature-dependent built-in potential in organic semiconductor devices

Kemerink, Martijn; Kramer, JM Jan Maarten; Gommans, Hhp; Janssen, Raj René

doi:10.1063/1.2205007

Cited by 66 publications

(53 citation statements)

References 14 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The effect of chargecarrier diffusion on V 0,EA is expected to decrease with decreasing temperature, as it is due to space charge in the device. A similar effect has already been observed by Kemerink et al 30 for the temperature dependence of the onset voltage in poly-phenylene-vinylene ͑PPV͒ based devices. To our point of view, the built-in voltage is then given by the value of the onset voltage, extrapolated to zero temperature.…”

Section: Experimental Results and Analysissupporting

confidence: 70%

Relation between the built-in voltage in organic light-emitting diodes and the zero-field voltage as measured by electroabsorption

et al. 2010

Self Cite

View full text Add to dashboard Cite

For developing understanding of the current density onset voltage and injection barriers in organic lightemitting diodes ͑OLEDs͒, a precise determination of the built-in voltage, V bi , is of crucial importance. Commonly, V bi is assumed to be equal to the voltage V 0,EA at which in an electroabsorption ͑EA͒ experiment the reflection of light at the OLED is found to become insensitive to a small voltage modulation. However, this assumption is shown to lead to significant errors for devices with well-injecting contacts. From an analysis of EA experiments for hole-only devices containing a polyfluorene-based copolymer, it is shown that V 0,EA may be interpreted as an effective current density onset voltage, agreeing with the commonly accepted picture, but that for these devices V bi is ϳ0.5 V larger than V 0,EA . This is found to be consistent with predictions of V 0,EA from model calculations of the electric field and light-absorption profiles in the semiconducting layer.

show abstract

Section: Experimental Results and Analysissupporting

confidence: 70%

Relation between the built-in voltage in organic light-emitting diodes and the zero-field voltage as measured by electroabsorption

et al. 2010

Self Cite

View full text Add to dashboard Cite

show abstract

“…At fi nite temperatures for ohmic contacts, the diffuse layer makes an electrostatic band bending that may lower the V bi perceptibly at the 0.1-V level, and thus cannot be neglected. [11][12][13] This electrostatic band bending is computed self-consistently here through the Poisson and drift-diffusion-generation equations.…”

Section: Experimental Validation Of the Optical Modelmentioning

confidence: 99%

“…Recent literature for example has tended to emphasize the correlation of V oc with disparate sources of losses, including binding energy of the charge-transfer exciton, [ 8 ] internal recombination, [ 9 ] or sub-gap absorption through a quasi-equilibrium detailed balance. [ 10 ] Nevertheless the V bi is a more fundamental parameter of the cell [11][12][13] and hence a natural starting point to understand the factors that limit V oc in high-performance organic solar cells. However the V bi of even prototypical P3HT:PCBM cells has not been directly established, but estimated between 0.6 and 0.9 V. [ 14 ] Because of strong para meter coupling, this hampers Here, using crosslinked P3HT network:PCBM cells with predefi ned ultrafi ne donor-acceptor morphology and very high internal quantum effi ciencies, the built-in potential V bi is measured to decouple and reliably extract other key parameters of the cells.…”

mentioning

confidence: 99%

Evaluation of Built‐In Potential and Loss Mechanisms at Contacts in Organic Solar Cells: Device Model Parameterization, Validation, and Prediction

Liu

Png

Tan

et al. 2013

Advanced Energy Materials

View full text Add to dashboard Cite

The power conversion effi ciency (PCE) of solar cells or photovoltaic cells is given by the product of their short-circuit photocurrent density J sc , fi ll factor (FF) and open-circuit voltage V oc . For organic solar cells, in which the photoactive layer (PAL) is an organic semiconductor (OSC) comprising intimatelymixed donor (D) and acceptor (A) phases, these performance parameters depend on a complex interplay of several processes, some more strongly related to materials and processing while others to cell design. [ 1 ] In brief, the overall effi ciency of the solar-to-electrical energy conversion chain depends on the following effi ciencies. The cell absorption effi ciency for the incident solar photons is determined primarily by the PAL but infl uenced by optical interference effects. The photocarrier generation effi ciency depends on the fraction of excitons that can dissociate to charge-separated pairs through processes that are still under debate, although this is known to be a property of the electronic structure and morphology of the DA interface. Then the collection effi ciency is determined by internal (non-geminate) recombination losses. The maximum electrochemical potential difference available from the carriers depends on electronic structure and other effects. The current-voltage ( JV ) characteristic under solar irradiation refl ects the outcome of all of these processes, which are heavily coupled. [2][3][4] Nevertheless signifi cant advances have occurred in some aspects, such as the correlation of cell properties with PAL and the DA morphology. [ 5 ] The maximum V oc available has been suggested to vary linearly with the energy gap between the highest-occupied molecular orbital (HOMO) band edge of D and the lowest unoccupied molecular orbital (LUMO) band edge of A, subjected to a loss of a few tenths of an eV, often thought to be 0.3 eV. [ 6,7 ] However a number of electrical parameters of the cells are not known accurately, including the relevant electronic energies, and so it is not possible to be certain about the magnitude of this offset. Recent literature for example has tended to emphasize the correlation of V oc with disparate sources of losses, including binding energy of the charge-transfer exciton, [ 8 ] internal recombination, [ 9 ] or sub-gap absorption through a quasi-equilibrium detailed balance. [ 10 ] Nevertheless the V bi is a more fundamental parameter of the cell [11][12][13] and hence a natural starting point to understand the factors that limit V oc in high-performance organic solar cells. However the V bi of even prototypical P3HT:PCBM cells has not been directly established, but estimated between 0.6 and 0.9 V. [ 14 ] Because of strong para meter coupling, this hampers Here, using crosslinked P3HT network:PCBM cells with predefi ned ultrafi ne donor-acceptor morphology and very high internal quantum effi ciencies, the built-in potential V bi is measured to decouple and reliably extract other key parameters of the cells. Using the refi ned device parameters, the ge...

show abstract

“…The low injection barrier at the anode of the ID583/C 60 devices caused a charge accumulation and thus a band bending. 27,49 In the cells with a 7 nm donor layer, the D/A interface, where the charge dissociation occurred, was located very close to the anode. As a result, the increased field in this region enhanced the charge dissociation process.…”

Section: A Influence Of the Cell Thicknessmentioning

confidence: 99%

Field-dependent exciton dissociation in organic heterojunction solar cells

et al. 2012

View full text Add to dashboard Cite

In organic heterojunction solar cells, the generation of free charge carriers takes place in a multistep process which involves charge transfer (CT) states, that is, bound electron-hole pairs at the interface between donor and acceptor molecules. Past efforts to model the CT-state dissociation during solar cell operation were not able to consistently reproduce the experimentally observed field and temperature dependence. This discrepancy between model and experiment was partly due to the field-dependent free charge carrier collection process, which plays an important role in the widely used bulk heterojunction cell configuration and superimposes a possible field-dependent charge carrier generation process. In order to distinguish between generation and collection of free charge carriers, we propose the planar heterojunction cell configuration as a model system to study the field-dependent charge carrier generation process in organic heterojunction solar cells. We apply this model system to check current CT-state dissociation models against experimental data. Although the models can quantitatively account for the photocurrent's dependence on the applied voltage and the device thickness, they fail to account for the virtually negligible temperature dependence of the field-dependent charge-generation process. This discrepancy is traced back to a common feature of the models: an Arrhenius-like temperature dependence, distinctive of all processes involving a thermally activated jump over an energy barrier. As a solution to the problem, we introduce an exciton dissociation model based on a field-dependent tunnel process and demonstrate its consistency with the experimental observations. Our results indicate that the current microscopic picture of the charge-generation process in organic heterojunction solar cells being limited by the CT-state dissociation process needs to be reconsidered.

show abstract

Temperature-dependent built-in potential in organic semiconductor devices

Cited by 66 publications

References 14 publications

Relation between the built-in voltage in organic light-emitting diodes and the zero-field voltage as measured by electroabsorption

Relation between the built-in voltage in organic light-emitting diodes and the zero-field voltage as measured by electroabsorption

Evaluation of Built‐In Potential and Loss Mechanisms at Contacts in Organic Solar Cells: Device Model Parameterization, Validation, and Prediction

Field-dependent exciton dissociation in organic heterojunction solar cells

Contact Info

Product

Resources

About