Organic light emitting ambipolar field effect transistor with distributed light emission
View Patent ↗An organic ambipolar light emitting field effect transistor having an architecture with layers stacked one over the other, adapted to generate a diffused illumination is described. The transistor has a gate electrode, a dielectric layer superposed to the gate electrode, an ambipolar channel superposed to the dielectric layer having a P-type semiconductor layer whose energy band is determined by its highest occupied molecular orbital HOMO-SC p and lowest unoccupied molecular orbital LUMO-SC p , a N-type semiconductor layer whose energy band is determined by its highest occupied molecular orbital HOMO-SC n and lowest unoccupied molecular orbital LUMO-SC n and a light emitting layer adapted to allow recombination of charge carriers of opposite sign, interposed between the P-type semiconductor layer and the N-type semiconductor layer, whose energy band is determined by its highest occupied molecular orbital HOMO-R and lowest unoccupied molecular orbital LUMO-R, respectively; a source electrode adapted to inject charges of a first type and a drain electrode adapted to inject charges of a second type, said source electrode and drain electrode being in contract with a same layer of said P-type or N-type semiconductor layers, the other of said semiconductor layers being in contact with the dielectric layer.
1. An electroluminescent ambipolar organic field-effect transistor, having an architecture with stacked layers, comprising:
a gate electrode,
a dielectric layer superposed to said gate electrode,
an ambipolar channel superposed to said dielectric layer, comprising
a P-type semiconductor layer whose energy band is determined by its highest occupied molecular orbital HOMO-SCp and lowest unoccupied molecular orbital LUMO-SCp,
an N-type semiconductor layer (SCn) whose energy band is determined by its highest occupied molecular orbital HOMO-SCn and lowest unoccupied molecular orbital LUMO-SCn, and
a light emitting layer adapted to allow recombination of charge carriers of opposite sign, interposed between said P-type semiconductor layer and said N-type semiconductor layer, said light emitting layer being alternatively composed of either a single material whose energy band is determined by its highest occupied molecular orbital HOMO-R and lowest unoccupied molecular orbital LUMO-R, or a Host-Guest system composed of a Host material and one or more Guest materials, the Host material having an energy band determined by its highest occupied molecular orbital HOMO-H and lowest unoccupied molecular orbital LUMO-H and the one or more Guest materials having each an energy band determined by respective highest occupied molecular orbital HOMO-G and lowest unoccupied molecular orbital LUMO-G,
a source electrode adapted to inject charges of a first type and
a drain electrode adapted to inject charges of a second type, said source electrode and drain electrode being in contact with a top layer of said P-type or N-type semiconductor layers, a bottom layer of said P-type or N-type semiconductor layers being in contact with the dielectric layer, wherein
a ratio between a value of an effective field-effect mobility at an interface between the top layer of said P-type or N-type semiconductor layers and said light emitting layer and a value of an effective field-effect mobility at an interface between the bottom layer of said P-type or N-type semiconductor layers and said dielectric layer is in the range from 0.05 to 20;
in the case in which the P-type semiconductor layer is in contact with the dielectric layer and said light emitting layer is composed of a single material:
the difference between the levels HOMO-R and HOMO-SCn is comprised between 0.2 eV and 1 eV,
the difference between the levels LUMO-R and LUMO-SCn is comprised between 0.2 eV and 0.8 eV,
the difference between the levels HOMO-R and HOMO-SCp is comprised between 0 eV and 0.5 eV,
the difference between the levels LUMO-R and LUMO-SCp is comprised between −1 eV and 0 eV;
in the case in which the N-type semiconductor layer is in contact with the dielectric layer and said light emitting layer is composed of a single material:
the difference between the levels HOMO-R and HOMO -SCn is comprised between 0 eV and 1 eV,
the difference between the levels LUMO-R and LUMO-SCn is comprised between −0.5 eV and 0 eV,
the difference between the levels HOMO-R and HOMO-SCp is comprised between −0.2 eV and −0.8 eV,
the difference between the levels LUMO-R and LUMO-SCp is comprised between −0.2 eV and −1 eV;
in the case in which the P-type semiconductor layer is in contact with the dielectric layer and said light emitting layer is composed of a Host-Guest system:
the difference between the levels HOMO-H and HOMO-SCn is comprised between 0.2 eV and 1 eV,
the difference between the levels LUMO-H and LUMO-SCn is comprised between 0.2 eV and 3 eV,
the difference between the levels HOMO-H and HOMO-SCp is comprised between 0 eV and 0.5 eV,
the difference between the levels LUMO-H and LUMO-SCp is comprised between −1 eV and 3 eV, and
for all Guest materials:
the difference between the levels LUMO-G and LUMO-SCn is comprised between 0.3 eV and −1 eV,
the difference between the levels HOMO-G and HOMO-H is comprised between 0 eV and 1 eV;
in the case in which the N-type semiconductor layer is in contact with the dielectric layer and said light emitting layer is composed of a Host-Guest system:
the difference between the levels HOMO-H and HOMO-SCn is comprised between −3 eV and 1 eV,
the difference between the levels LUMO-H and LUMO-SCn is comprised between −0.5 eV and 0 eV,
the difference between the levels HOMO-H and HOMO-SCp is comprised between −0.2 eV and −3 eV,
the difference between the levels LUMO-H and LUMO-SCp is comprised between −0.2 eV and −1 eV, and
for all Guest materials:
the difference between the levels HOMO-G and HOMO-SCp is comprised between −0.3 eV and 1 eV, and
the difference between the levels LUMO-G and LUMO-H is comprised between 0 eV and −1 eV.
2. The transistor according to claim 1 , wherein said ratio is in the range from 0.7 to 1.3.
3. The transistor according to claim 1 , wherein the value of said effective field effect mobility at the interface between the top layer of said P-type or N-type semiconductor layers and said light emitting layer and the value of the effective field-effect mobility at the interface between the bottom layer of said P-type or N-type semiconductor layers and said dielectric layer are at least 10 −3 cm 2 /Vs.
4. The transistor according to claim 1 , wherein a distance between said source electrode and drain electrode is between 20 μm and 300 μm.
5. The transistor according to claim 1 , wherein a surface roughness at the interfaces between said light emitting layer and each of the P-type or N-type semiconductor layers is in the range from 0.2 nm to 10 nm.
6. The transistor according to claim 5 , wherein said surface roughness is in the range from 0.2 nm to 5 nm.
7. The transistor according to claim 1 , wherein the materials forming said ambipolar channel have a purity between 99.8% and 99.999%.
8. The transistor according to claim 7 , wherein said purity is between 99.99% and 99.999%.
9. The transistor according to claim 1 , wherein said source electrode and rain electrode are made of a same material.
10. The transistor according to claim 1 , wherein in the case in which the P-type semiconductor layer is in contact with the dielectric layer and said light emitting layer is composed of a single material:
the difference between the levels LUMO-R and LUMO-SCn is comprised between 0.2 eV and 0.6 eV,
the difference between the levels HOMO-R and HOMO-SCp is comprised between 0.2 eV and 0.5 eV, and
the difference between the levels LUMO-R and LUMO-SCp is comprised between −1 eV and −0.2 eV;
in the case in which the N-type semiconductor layer is in contact with the dielectric layer and said light emitting layer is composed of a single material:
the difference between the levels HOMO-R and HOMO-SCn is comprised between 0.2 eV and 1 eV,
the difference between the levels LUMO-R and LUMO-SCn is comprised between −0.5 eV and −0.2 eV, and the difference between the levels HOMO-R and HOMO-SCp is comprised between −0.2 eV and −0.6 eV.