Dear All,
I have fabricated several lateral top contact OFETs, some of which were a mix of PaMS blended TIPS-pc and PbS QD.
I noticed lower photosensitivity and photosensitivity after ading the QD into my active layer, while the mobility of all devices was the same, given that all devices showed good MOSFET-like I-V curves.
I am trying to identify the reason behind the degredation of the Photosensitivity and the Responsivity., Any insight or relevant litereture recommendations will be greately appreciated
Photo sensitivity and photo responsiveness depends on band edge that links with the applied photonic band. I mean; on the availability of free carrier for particular excitation band of applied light. But the electric field response might have strong relationship with the energy level of the applied potential that differ the energy level due to optical excitation energy.
When you deposit multi-layered structures in OFET, interface recombination of generated minority carriers are possible. Also your QD thickness and material may matter in addition to band alignment at the top edge of QD and bottom edge of QD for the amplification and absorption of minority carriers within the band gap you are concentration upon. In addition, all layer-to-layer impedance matching needs to be ensured and surface recombination velocity at all interface between layers should be negligibly small. My guess is within the band-gap region your device is operating, QD layer and the material choice are not fully optimized to give you optical amplification and high absorption. Please check these papers.
Recommend my answer if it is useful.
Sincerely,
Dr. Nabil Shovon Ashraf.
Dear Sara,
welcome,
In addition to what has been said by the colleagues above. In addition to the field effect current, there will be the photo conductive current of the substrate layer Idph. The parameters controlling the Idph are:
The absorption coefficient alpha of the incident solar radiation,
The thickness of the material suffice int to absorb to absorb the incident radiation. The thickness required is = 1/alpha,
The absorbed photons will generate excitons which are electrostatic ally bound electron hole pairs. The excitons binding energy is inversely proportional to the dielectric constant epsilon. In organic materials epsilon is relatively low compared to the metallic semiconductor materials.
These excitons can survive only for specific survival time called the exciton life time. To generate free electrons and holes these the excitons must be dissociate. This is accomplished by the applied electric field associated with drain to source voltage VDS. The thermal energy can help in the dissociation process. So, the dissociation efficiency depends on the value of VDS. It increases with VDS.
Not only that the fee electron holes must be disposed before recombining inside the semicondcutor material. It is so one an excess of electrons and holes are formed in as semiconductor material they will survive only a period of time called the lifetime. So, the electric field must extract them to the collecting electrodes before recombining.
This can be achieved by by making the length of the channel smaller than the diffusion length.
So, as we see there are loss mechanisms that must be minimized to increase the responsivity of the device to the incident radiation.
The device nust be optimized to achieve as high responsivity as possible.
Best wishes
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