Energy sensitization of acceptors and donors in organic photovoltaics
Disclosed herein are organic photosensitive optoelectronic devices comprising acceptor and/or donor sensitizers to increase absorption and photoresponse of the photoactive layers of the devices. In particular, devices herein include at least one acceptor layer and at least one donor layer, wherein the acceptor layer may comprise a mixture of an acceptor material and at least one sensitizer, and the donor layer may comprise a mixture of a donor material and at least one sensitizer. Methods of fabricating the organic photosensitive optoelectronic devices are also disclosed.
1. An organic photosensitive optoelectronic device comprising:
two electrodes in superposed relation;
an organic acceptor layer and a mixed organic donor layer located between the two electrodes;
a buffer layer between one of the two electrodes and the organic acceptor layer; and
a charge transfer layer between the other of the two electrodes and the mixed organic donor layer,
wherein the mixed organic donor layer comprises a mixture of a donor material chosen from phthalocyanines, subphthalocyanines, naphthalocyanines, merocyanine dyes, boron-dipyrromethene (BODIPY) dyes, thiophenes, polyacenes, and squaraine (SQ) dyes and at least one donor sensitizer chosen from subphthalocyanines, porphyrins, phthalocyanines, dipyrrins and metal complexes thereof, boboron-dipyrromethene (BODIPY) dyes, squaraines, oligothiophenes, and acenes and derivatives thereof, wherein the donor material and the at least one donor sensitizer are chosen to satisfy the following conditions:
the at least one donor sensitizer has a lowest triplet excited state energy (E T-DSens ) greater than or equal to a lowest triplet excited state energy (E T-D ) of the donor material;
the at least one donor sensitizer has an oxidation potential greater than or equal to an oxidation potential of the donor material; and
if the at least one donor sensitizer and the donor material form a charge transfer (CT) state having a CT state energy, the CT state energy is greater than or equal to the lowest triplet excited state energy (E T-D ) of the donor material,
wherein the at least one donor sensitizer results in an unaltered short circuit current (J SC ) and an increase in power conversion efficiency (η p ).
2. The device of claim 1 , wherein the donor material and the at least one donor sensitizer are chosen such that the at least one donor sensitizer has a lowest singlet excited state energy (E S-DSens ) greater than or equal to a lowest singlet excited state energy (E S-D ) of the donor material.
3. The device of claim 1 , wherein the donor material and the at least one donor sensitizer are chosen such that the CT state energy is greater than or equal to a lowest singlet excited state energy (E S-D ) of the donor material.
4. The device of claim 1 , wherein the mixture of the donor material and the at least one donor sensitizer form a solid solution.
5. The device of claim 1 , wherein the at least one donor sensitizer has an absorptivity of at least 10 3 cm −1 at one or more wavelengths ranging from 350 to 950 nm.
6. The device of claim 1 , wherein the at least one donor sensitizer has a maximum absorptivity at one or more wavelengths, the maximum absorptivity of the at least one donor sensitizer being at least twice as large as an absorptivity of the donor material at the one or more wavelengths.
7. The device of claim 1 , wherein the mixture of a donor material and at least one donor sensitizer has a donor:sensitizer ratio in a range of 10:1 to 1:2.
8. The device of claim 1 , wherein the mixed donor layer has a thickness in a range of 20 to 70 nm.
9. The device of claim 1 , further comprising an intermediate donor layer located between the mixed donor layer and the acceptor layer, wherein the intermediate donor layer consists of the donor material and forms a donor-acceptor heterojunction with the acceptor layer.
10. The device of claim 9 , wherein the intermediate donor layer has a thickness in a range of 10 to 50 nm.