what is the advantages and disadvantages of using electron and hole transport layers in organic solar cells?
Dear Ali,
This is a very nice question and the answer is that there is no disadvantages of usinf hole/electron transport layers in organic solar cells (except of course of the increased device complexity and cost). If you want your solar cell to perform well you HAVE to use those layers in order to achieve: 1) favorable energy level alignment at the interfaces of the active layer with each contact, 2) increased charge carrier selectivity at each contact, 3) reduced recombination losses at the interfaces mentioned above, 4) increased charge transport/extraction, 5) improved built-in field, 6) Improved stability and lifetime.
Without those (appropriate) layers your device will exhibit poor performance and short lifetime.
Dear Ali
The answer of Maria is complete, but it needs to study for each material that is used for HTL or ETL. In some cases, they can accelerate the degradation of cell by releasing some impurities.
Regards
I agree with Dr. Maria. You have to carefully choose the material for ETL and HTL, and these layers only enhance the efficiency of Organic solar cells
I fully agree with the previous answers. There is no such thing as disadvantages but only advantages depending on what end you need them to. Some of them may improve one area of the device but may be of no use in the others (efficiency, processing and stability).
Thank you for your complete answers. but there is a question. All things you have mentioned, are electrical effects. but what is the role of optical effects in electron and hole transport layers such as interference effects, (optical) generation of excitons at ETL & HTL regions, etc in performance of an organic solar cell?
In Organic solar cells ETL and HTL help in efficient charge extraction at the electrodes. in contrast in PLEDs for example the main role of PEDOT:PSS is to compensate for ohmic losses and promote hole injection. Depending on the thickness of the active layer (AL) they can have diverse effects. Note that the important thing here is the AL. Others only come in to improve. So absorption needed to be promoted in the AL. And since you have stucks of layers there are obviously optical interferences due to all these layers. A lot happens at the interfaces of these layers (morphology, contact length, defects) - light scattering, reflection for example. Note that you can enhance efficiency of your device using judicious optical pathways. These are complex issues. Read more papers especially from W. Brütting (J. Appl. Phys., Vol. 90, No. 7, 1 October 2001) and also from Sven Rühle. I hope this helps
Dear Ali
As you know, the optical behavior of these cells are modeled by Transfer Matrix Method. In this model each layer is introduced by its optical constants (n, k). During the calculation of light intensity in this device, two matrix are investigated: the first is interface matrix which relates to the effect of the interface between layers, the second is propagation matrix which relates to the energy loss in each layer. So, when a HTL is used after ITO, there would be some losses due to its absorption coefficient and refraction in its interfaces. But, when an ETL is used before cathode, it can cause absorption impoverishment in the device, because most of the ETL can be used as optical spacer which reduces the reflection from Al surface. In general, because of small thicknesses of all layers in these devices, the interference effects are significant. The final decision about the optical effect of each layer should be taken by using TMM. this method can determine the optimum thicknesses for each layer in this devices.
I hope it helps.
Farzaneh
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