Semitransparent organic photovoltaic (OPV) cells are of interest due to their potential for fulfilling building integrated PV needs such as deployment on windows and other architectural surfaces. Moreover, semitransparent OPV cells can also be integrated into tandem- and multi-junction structures to achieve a high power conversion efficiency (PCE) along with acceptable transparency for these applications. However, the PCE of semitransparent OPV cells remains relatively low since they have been primarily based on bilayer or mixed heterojunction (HJ) structures.
The present disclosure is directed to inverted, semitransparent photovoltaic cells, particularly semitransparent OPVs based on both mixed and hybrid planar-mixed heterojunctions (PM-HJ). The device structures are inverted to allow for the use of transparent indium tin oxide (lTO) contacts for both anode and cathode. Cathode contact is made on the substrate surface using a hole blocking/electron selective sol-gel ZnO layer as a cathode buffer on top of an ITO contact The ZnO has a high electron mobility9 of ˜10 cm2/V·s. 98% transmission in the visible and near infrared (NIR) spectral regions, and a work function of 4.5 eV10, leading to efficient electron collection and low optical loss. In addition, ZnO-based inverted structures eliminate thin but optically lossy metal layers that have been reported previously. It is worth noting that conventional OPV structures using wide energy gap molecules, e.g. bathophenanthroline (BPhen), as cathode buffers cannot employ symmetric ITO contacts due to the lack of electron-transporting defect states induced by the electrode deposition, whereas inverted structures enable the implementation of metal oxides, e.g. MoO3, as the buffer for the top electrode to efficiently extract charge carriers without the concern of defect states.
Table I depicts performance of inverted, semitransparent OPV cells
The inverted semitransparent PM-HJ OPV cells exhibit PCE=3.9±0.2% under simulated AM 1.5G illumination at one sun intensity with an average transmission of
In a first embodiment of the present disclosure, inverted semitransparent mixed HJ OPV cells are fabricated based on the donor, tetraphenyldibenzoperiflanthene (DBP), and the acceptor, C70. The first embodiment of the present disclosure is thus directed to a semitransparent photovoltaic cell, comprising a cathode layer of indium tin oxide; a cathode buffer layer comprised of ZnO, located between the cathode layer and a mixed heterojunction layer; the mixed heterojunction layer comprised of tetraphenyldibenzoperiflanthene and C70, located between the cathode buffer layer and an anode buffer layer; the anode buffer layer comprised of MoO3, located between the mixed heterojunction layer and an anode layer; an anode layer comprised of indium tin oxide, adjacent to the anode buffer layer, wherein the photovoltaic cell is in an inverted configuration. In a particular embodiment, a 30 nm thick DBP:C70 (1:8 vol. ratio) blend has an average transmission of
The cathode buffer layer may have a thickness ranging from 5 to 500 nm, such as 5 to 250 nm, 5 to 150 nm, 10 to 125 nm, 10 to 100 nm, 10 to 90 nm, 20 to 70 nm, 20 to 60 nm and 20 to 40 nm. In certain embodiments, the cathode buffer layer has a thickness of 30 nm. The mixed heterojunction layer may have a thickness ranging from 5 to 500 nm, such as 5 to 250 nm, 5 to 150 nm, 10 to 125 nm, 10 to 100 nm, 10 to 90 nm, and 30 to 70 nm. In certain embodiments, the mixed heterojunction layer has a thickness of 30 nm, 40 nm, 50 nm, 60 nm, or 70 nm. The mixed heterojunction layer composition may range from a volume ratio of 1:1 to 1:16 of tetraphenyldibenzoperiflanthene and C70, such as 1:12, 1:10, 1:8, 1:6, and 1:4. The anode buffer layer may have a thickness ranging from 2 to 500 nm, such as 5 to 250 nm, 5 to 100 nm, and 10 to 50 nm. In certain embodiments, the anode buffer layer has a thickness of 10 nm, 20 nm, 30 nm, 40 nm, or 50 nm.
In another embodiment of the present disclosure, an inverted photovoltaic cell comprises a cathode and an anode, both comprised of indium tin oxide; a cathode buffer, comprised of ZnO, adjacent to the cathode; an anode buffer, comprised of MoO3, adjacent to the anode; and a mixed heterojunction comprised of tetraphenyldibenzoperiflanthene and C70, adjacent to the cathode buffer and the anode buffer. The cathode buffer may have a thickness ranging from 5 to 500 nm, such as 5 to 250 nm, 5 to 150 nm, 10 to 125 nm, 10 to 100 nm, 10 to 90 nm, 20 to 70 nm, 20 to 60 nm and 20 to 40 nm. In certain embodiments, the cathode buffer has a thickness of 30 nm. The mixed heterojunction may have a thickness ranging from 5 to 500 nm, such as 5 to 250 nm, 5 to 150 nm, 10 to 125 nm, 10 to 100 nm, 10 to 90 nm, and 30 to 70 nm. In certain embodiments, the mixed heterojunction has a thickness of 30 nm, 40 nm, 50 nm, 60 nm, or 70 nm.
The mixed heterojunction composition may range from a volume ratio of 1:1 to 1:16 of tetraphenyldibenzoperiflanthene and Co, such as 1:12, 1:10, 1:8, 1:6, and 1:4. The anode buffer may have a thickness ranging from 2 to 500 nm, such as 5 to 250 nm, 5 to 100 nm, and 10 to 50 nm. In certain embodiments, the anode buffer has a thickness of 10 nm, 20 nm, 30 nm, 40 nm, or 50 nm.
The J-V and EQE characteristics are shown in
To further understand the dependence of FF on x, the specific series resistance (RSA) is obtained vs. the active layer thickness by filling the dark J-V characteristics to:
where Js the saturation current density in the dark, n is the ideality factor associated with the donor (acceptor) layer, kB is the Boltzmann constant, T is the temperature, q is the elementary charge, and Jph is the photocurrent density. χ is the ratio of the polaron-pair dissociation rate at the heterojunctions between donor and acceptor at V to its value at V=0. We find RSA=2.9±0.1 Ω·cm2 for 30 nm thick OPV cells, and increases to 5.8±0.1 Ω·cm2 for 70 nm thick devices: a result of reduced charge collection efficiency (and hence FF) of thicker donor/acceptor mixed regions.
The inverted PM-HJ architecture consisting of a donor/acceptor mixture grown onto a neat acceptor layer is useful in reducing the active region series resistance by improving charge collection. Thus, an additional embodiment of the present disclosure is a semitransparent organic photovoltaic cell that comprises a cathode layer of tin oxide; a cathode buffer layer comprised of ZnO, located between the cathode layer and a planar-mixed heterojunction layer; the planar-mixed heterojunction layer comprised of a planar layer of C70 and a mixed layer of tetraphenyldibenzoperiflanthene and C70, located between the cathode buffer layer and an anode buffer layer; the anode buffer layer comprised of MoO3, located between the mixed heterojunction layer and an anode layer; the anode layer comprised of indium tin oxide; wherein the photovoltaic cell is in an inverted configuration.
The cathode buffer layer may have a thickness ranging from 5 to 500 nm, such as 5 to 250 nm, 5 to 150 nm, 10 to 125 nm, 10 to 100 nm, 10 to 90 nm, 20 to 70 nm, 20 to 60 nm and 20 to 40 nm. In certain embodiments, the cathode buffer layer has a thickness of 30 nm. The planar heterojunction layer may have a thickness ranging from 2 to 16 nm, such as from 5 to 15 nm or 7 to 11 nm. In certain embodiments, the planar heterojunction layer has a thickness of 9 nm. The mixed heterojunction layer may have a thickness ranging from 5 to 500 nm, such as 5 to 250 nm, 5 to 150 nm, 10 to 125 nm, 10 to 100 nm, 10 to 90 nm, 20 to 70 nm, 20 to 60 nm, and 30 to 70 nm. In certain embodiments, the mixed heterojunction layer has a thickness of 51 nm. The percentage of planar heterojunction layer thickness in the planar-mixed heterojunction layer may range from 2 to 50%, such as 5 to 50%, 5 to 40%, 5 to 30%, 5 to 25%, 5 to 20%, 5 to 10%, 10 to 50%, 10 to 40%, 10 to 30%, 10 to 25%, 10 to 20%, 15 to 50%, 15 to 40%, 15 to 30%, 15 to 25%, 20 to 50%, 20 to 40%, and 20 to 30%. In certain embodiments, the percentage of planar heterojunction layer thickness in the planar-mixed heterojunction is 15%. The mixed heterojunction layer composition may range from a volume ratio of 1:1 to 1:16 of tetraphenyldibenzoperiflanthene and C70, such as 1:12, 1:10, 1:8, 1:6, and 1:4. In certain embodiments, this ratio is 1:8. The anode buffer layer may have a thickness ranging from 2 to 500 nm, such as 5 to 250 nm, 5 to 100 nm, and 10 to 50 nm. In certain embodiments, the anode buffer layer has a thickness of 10 nm, 20 nm, 30 nm, 40 nm, or 50 nm. In certain embodiments, the semitransparent organic photovoltaic cell further comprises a second heterojunction layer.
In another embodiment of the present disclosure, an inverted photovoltaic cell comprises a cathode and an anode, both comprised of indium tin oxide; a cathode buffer, comprised of ZnO, adjacent to the cathode; an anode buffer, comprised of MoO3, adjacent to the anode; and a planar-mixed heterojunction, comprising C70 adjacent to the cathode buffer and a mixture of tetraphenyldibenzoperiflanthene and C70 adjacent to the C70 and the anode buffer. The cathode buffer may have a thickness ranging from 5 to 500 nm, such as 5 to 250 nm, 5 to 150 nm, 10 to 125 nm, 10 to 100 nm, 10 to 90 nm, 20 to 70 nm, 20 to 60 nm and 20 to 40 nm. In certain embodiments, the cathode buffer has a thickness of 30 nm. The C70 layer may have a thickness ranging from 2 to 25 nm, such as from 5 to 15 nm or 7 to 11 nm. In certain embodiments, the C70 layer is 9 nm thick. The layer comprising a mixture of tetraphenyldibenzoperiflanthene and C70 may have a thickness ranging from 5 to 500 nm, such as 5 to 250 nm, 5 to 150 nm, 10 to 125 nm, 10 to 100 nm, 10 to 90 nm, 30 to 70 nm, and 40 to 60 nm. In certain embodiments, the layer comprising the mixture of tetraphenyldibenzoperiflanthene and Co has a thickness of 51 nm. The composition of the mixture of tetraphenyldibenzoperiflanthene and C70 may range from a volume ratio of 1:1 to 1:16, such as 1:12, 1:10, 1:8, 1:6, and 1:4. In certain embodiments this ratio is 1:8. The anode buffer layer may have a thickness ranging from 2 to 500 nm, such as 5 to 250 nm, 5 to 150 nm, 10 to 125 nm, 10 to 100 nm, 10 to 90 nm, and 10 to 50 nm. In certain embodiments, the anode buffer layer has a thickness of 10 nm, 20 nm, 30 nm, 40 nm, or 50 nm.
In certain embodiments, the neat C70 layer thickness of 9 nm is roughly equal to its exciton diffusion length, leading to efficient exciton dissociation at the acceptor/blend interface. The C70/DBP:C70 film has
To further understand the improved combination of transparency and efficiency of the PM-HJ architecture, we measured the internal quantum efficiency (IQE), i.e. the ratio of photogenerated carriers collected at the electrodes to the absorbed photons in the active region. The PM-HJ shows reduced absorption, calculated using transfer matrices, compared to the mixed HJ, particularly between the wavelengths of λ=550 nm to 700 nm (see
In another embodiment of the present disclosure, a tandem photovoltaic cell incorporates two PM-HJ sub-cells that absorb in different spectral regions; specifically, the embodiment contains a front sub-cell, a charge generation layer, and a back sub-cell. In some embodiments, the front sub-cell comprises a cathode layer comprised of indium tin oxide; a cathode buffer layer configured next to the cathode and comprised of ZnO; a planar-mixed heterojunction, comprised of a planar layer of C70 configured next to the cathode buffer layer and a mixed layer of 2-((7-(5-(dip-tolyamino)thiophen-2-yl)benzo[c][1,2,5]thiadiazol4yl)methylene)malononitrile and C60 configured next to the planar layer and the charge generation layer. In some embodiments, the front sub-cell may contain a mixed heterojunction, rather than a planar-mixed heterojunction. In some embodiments the charge generation layer may comprise a layer of MoO3, configured next to the mixed layer of the front sub-cell; a layer of Ag, configured next to the layer of MoO3; and a mixed layer comprising bathophenanthroline and C70, configured next to the layer of Ag. In some embodiments, the back sub-cell comprises a planar-mixed heterojunction, comprised of a C70 planar layer configured adjacent to the mixed layer of the charge generation layer, and a mixed layer of tetraphenyldibenzoperiflanthene and C70, configured adjacent to the C70 planar layer; a layer of MoO3, configured adjacent to the mixed layer of the heterojunction; and a layer of indium tin oxide, configured adjacent to the layer of MoO3. In some embodiments, the back sub-cell may contain a mixed heterojunction, rather than a planar-mixed heterojunction.
The cathode buffer layer may range in thickness from 5 to 500 nm, such as 5 to 250 nm, 5 to 150 nm, 10 to 125 nm, 10 to 100 nm, 10 to 90 nm, 20 to 70 nm, 20 to 60 nm and 20 to 40 nm. In certain embodiments, the cathode buffer layer has a thickness of 30 nm. The thickness of the front sub-cell planar heterojunction layer may range from 1 to 16 nm, such as from 2 to 11 nm or 3 to 8 nm. In certain embodiments, the front sub-cell planar heterojunction layer is 5 nm.
The front sub-cell mixed heterojunction layer may range from thicknesses of 5 to 500 nm, such as 5 to 250 nm, 5 to 150 nm, 10 to 125 nm, 10 to 100 nm, 10 to 90 nm, and 30 to 70 nm. In certain embodiments, the front sub-cell mixed heterojunction layer has a thickness of 60 nm. The front sub-cell mixed heterojunction layer composition may range from a volume ratio of 5:1 to 1:5 of 2-((7-(5-(dip-tolyamino)thiophen-2-yl)benzo[c][1,2,5]thiadiazol4yl)methylene)malononitrile and C60, such as 4:1, 3:1, 2:1, 1:1, 1:2, 1:3, and 1:4. In certain embodiments, this ratio is 1:1.
The layer of MoO3 present in the charge generation layer may have a thickness ranging from 5 to 100 nm, such as 5 to 75 nm, 10 to 50 nm, 10 to 40 nm, 15 to 50 nm, 15 to 40 nm, and 15 to 30 nm. In certain embodiments, the layer of MoO3 present in the charge generation layer has a thickness of 20 nm. The layer of Ag present in the charge generation layer may range in thickness from 0.01 to 1 nm, such as 0.05 to 1 nm, 0.05 to 0.75 nm, 0.05 to 0.5 nm, 0.05 to 0.25 nm, 0.1 to 0.5 nm, and 0.1 to 0.25 nm. In certain embodiments, the layer of Ag present in the charge generation layer is 0.1 nm. The mixed layer of bathophenanthroline and C6 present in the charge generation layer may range in thickness from 2 to 50 nm, such as 2 to 40 nm, 2 to 30 nm, 2 to 20 nm, 3 to 40 nm, 3 to 30 nm, 3 to 20 nm, 4 to 30 nm, 4 to 20 nm, and 4 to 10 nm. In certain embodiments the mixed layer of bathophenanthroline and Co in the charge generation layer has a thickness of 5 nm. The composition of the mixed layer of bathophenanthroline and C60 in the charge generation layer may range from 5:1 to 1:5 by volume, such as 4:1, 3:1, 2:1, 1:1, 1:2, 1:3, and 1:4. In certain embodiments the volume ratio of bathophenanthroline and Co is 1:1.
The back sub-cell planar heterojunction layer may have a thickness ranging from 1 to 16 nm, such as from 2 to 11 nm or 5 to 9 nm. In certain embodiments, the back sub-cell planar heterojunction layer is 7 nm. The back sub-cell mixed heterojunction layer may have a thickness ranging from 5 to 500 nm, such as 5 to 250 nm, 5 to 150 nm, 10 to 125 nm, 10 to 100 nm, 10 to 90 nm, and 30 to 70 nm. In certain embodiments, the back sub-cell mixed heterojunction layer has a thickness of 55 nm. The back sub-cell mixed heterojunction layer composition may range from a volume ratio of 1:1 to 1:16 of tetraphenyldibenzoperiflanthene and C70, such as 1:12, 1:10, 1:8, 1:6, and 1:4 In certain embodiments, the volume ratio of tetraphenyldibenzoperiflanthene and C70 is 1:8. The anode buffer layer may have a thickness ranging from 2 to 500 nm, such as 5 to 250 nm, 5 to 150 nm, 10 to 125 nm, 10 to 100 nm, 10 to 90 nm, and 10 to 50 nm. In certain embodiments, the anode buffer layer has a thickness of 20 nm.
Previously, thin metal films have been employed as semitransparent cathodes in OPV cells. These films, however, reflect and absorb a significant fraction of the incident light. which dramatically reduces the efficiency of the device when illuminated via the cathode vs. the anode. In the present disclosure, the use of metal-free, transparent ITO for both contacts eliminates these reflections and optical losses. As shown in the inset of
Various devices made according to the foregoing disclosures were made and tested. The embodiments described herein are further illustrated by the following non-limiting examples.
The photovoltaic cells were grown on glass substrates with pre-patterned ITO (4.2 mm×3.5 mm patterns, sheet resistance: 15 f/sq). The glass/ITO substrates were cleaned by successive ultrasonication in tergitol, deionized water, and a series of organic solvents, followed by ultraviolet ozone exposure for 10 min. The ITO surface was coated with ZnO deposited using a precursor solution prepared by dissolving 0.5 M zinc acetate dihydrate in 2-methoxyethanol with ethanolamine added as a stabilizer. The solution was passed through a 0.45 μm pore, polyvinylidene fluoride filter, and then spun-cast onto the substrates at 3000 rpm for 30 s. The film was then thermally annealed in ambient at 150° C. for 30 min. The substrates were transferred into a high vacuum chamber with a base pressure of 10−7 torr where organic layers were deposited. Top contacts consisting of 100 nm thick ITO were sputter-deposited at a base pressure of 7×10−8 torr and a deposition rate of 0.04 nm/s through a shadow mask with an array of 11 mm2 openings oriented perpendicular to the ITO contact patterns on the substrate. Completed devices were directly transferred into a high-purity N2-filled glove box with both H2O and O2 concentrations of <0.1 ppm. There, current density-voltage (J-V) and external quantum efficiency (EQE) measurements were performed. Transmission spectra of unpatterned films were obtained using a spectrometer (Perkin-Elmer, LAMBDA 1050).
This application claims the benefit of priority of U.S. Provisional Patent Application No. 62/869,359 filed on Jul. 1, 2019 the contents of which are incorporated herein by reference in their entirety.
This invention was made with government support under DE-EE0005310 and DE-EE0006708 awarded by the U.S. Dept. of Energy. The government has certain rights in the invention.
Number | Date | Country | |
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62869359 | Jul 2019 | US |