The Improvement of Luminous Uniformity of Large-Area Organic Light-Emitting Diodes by Using Auxiliary Electrodes
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe submitted article presents an investigation into improving the luminous uniformity of large-area blue OLEDs using auxiliary electrodes. It is an important topic for OLED fabricating technology.
1.Lots of grammatical and phrasing edits throughout would improve readability.
(1). In the full manuscript, the superscript, subscript need be corrected carefull. Such as: cm^2, 6x10^-6 torr, mA/cm^2,… etc.
(2). Figure 1 (a) and (b), device structures, could be combined. Only Fig. (b) needs to be shown in the manuscript.
(3). In pages 8-10, the paragraph format should be aligned left and right.
(4). In Fig.9, the annotation for Au should be capitalized.
(5). In page 12, line 330, the symbol (equation) of arithmetic mean is wrong.
2. In Fig.3 (a) and (b), the I-V and L-V characteristics of HATCN 3 and 5 nm seem no much different. And their thicknesses are very small and close. The discussions should be re-considered.
3. In page 10, lines 271-278, the sheet resistance values discussed are not matched with Table 2 shown. They should be check and explained.
4. The conclusion could be strengthened by stating the optimal auxiliary electrode configuration found in this study and quantifying the overall improvement in uniformity achieved.
Comments on the Quality of English LanguageMinor editing of English language required.
Author Response
Comment 1. Lots of grammatical and phrasing edits throughout would improve readability.
(1). In the full manuscript, the superscript, subscript need be corrected carefully. Such as: cm^2, 6x10^-6 torr, mA/cm^2,… etc.
Ans: In the revised whole manuscript, the superscript, subscript have been corrected carefully.
Action: Please see the red texts in the revised manuscript.
(2). Figure 1 (a) and (b), device structures, could be combined. Only Fig. (b) needs to be shown in the manuscript.
Ans: Only Fig. 1(b) from the original manuscript remains, and the figure caption has been written more clearly.
Action: Please see Fig. 1 in page 3 in the revised manuscript.
(3). In pages 8-10, the paragraph format should be aligned left and right.
Ans: All the paragraph format has been aligned left and right.
(4). In Fig. 9, the annotation for Au should be capitalized.
Ans: The annotations of Au in Fig. 9 have been revised as shown in the revised manuscript.
(5). In page 12, line 330, the symbol (equation) of arithmetic mean is wrong.
Ans: The symbol (equation) of arithmetic mean has been corrected as shown in page 11 lines 379 and 385.
Comment 2. In Fig.3 (a) and (b), the I-V and L-V characteristics of HATCN 3 and 5 nm seem no much different. And their thicknesses are very small and close. The discussions should be re-considered.
Ans: We have combined the 3 and 5 nm of HATCN as the same level of parameter, described as following:
*HATCN layers with a thickness of 3-5 nm exhibited higher current density and brightness compared to the 7 nm layer.
*A thinner HATCN layer (3-5 nm) generally facilitates better energy alignment, allowing for easier injection of holes from the anode (ITO) into the organic layer.
Action: Please see the page 4 lines 156-172 in the revised manuscript.
Comment 3. In page 10, lines 271-278, the sheet resistance values discussed are not matched with Table 2 shown. They should be checked and explained.
Ans: The sheet resistance values in Table 2 have been corrected. Please see the red numbers in Table 2 in the revised manuscript.
Comment 4. The conclusion could be strengthened by stating the optimal auxiliary electrode configuration found in this study and quantifying the overall improvement in uniformity achieved.
Ans: The conclusion has been rewritten according to the reviewer’s comments, part as below. Please see the conclusion part in the revised manuscript.
*In the nine square-block uniformity test, PET/ITO/OLEDs without auxiliary Au lines exhibited an overall luminance uniformity of only 74.1%. It was observed that the luminance decreases as the testing point moves away from the positive electrode contact clip. However, by incorporating auxiliary Au lines with a thickness of 15 nm, a line width of 0.1 mm, and a spacing of 5 mm (6 lines in total within the emitting area) on PET/ITO substrate, the overall uniformity in the nine-square block uniformity test improved significantly to 87.4%. When the density of the auxiliary Au lines was increased to a spacing of 2 mm (resulting in 16 lines), the overall uniformity slightly decreased to 84.6%. Nonetheless, the overall brightness of the blue OLED increased from 24.68 to 35.49 cd/m^2, making the flexible large-area blue OLED lighting panels appear noticeably brighter.
Reviewer 2 Report
Comments and Suggestions for AuthorsThis manuscript “The improvement of luminous uniformity of large-area organic 1 light-emitting diodes by using auxiliary electrodes”, was reported by Fuh-Shyang Juang. The results are interesting and can be accepted after clarifying some unclear parts.
1. Do you have the result for device structure with HATCH in Fig. 1b?
2. The uniformity about transmittance in nine area as Fig 11a and 12a should be discussed.
3. The reasons for the non-uniformity are from conductivity or transmittance?
4. The big area OLED device lifetime should be provided and discussed.
5. Due to the big area OLED, how to measure the current efficiency, brighter region or dark region, it should be disclosed.
6. How to measure the luminance at nine area, focus on the center or others?
Comments on the Quality of English LanguageLike some Superscripts and Subscripts are not showing in right way .
Author Response
Comment 1: Do you have the result for device structure with HATCH in Fig. 1b?
Ans: In original manuscript, In Fig. 1(b), the device structure is ITO/Auxiliary Au lines/PEDOT:PSS/HATCN /TAPC… In this study, all the devices use HATCN/TAPC as hole injection and transport layers. In the revised manuscript, we keep the Fig. 1(b) to be figure 1.
Action: Please see page 3 in the revised manuscript.
Comment 2: The uniformity about transmittance in nine area as Fig 11a and 12a should be discussed.
Ans: The anode structure is ITO/auxiliary Au lines. The PET/ITO substrate is purchased from commercial company, whose ITO film is very uniform. The Au lines were deposited with thermal evaporator at 8x10-6 torr, which are also uniform. So the uniformity of the transmittance of ITO/auxiliary Au lines in nine area is good enough. Due to sample size limitation of the UV-VIS measurement equipment, it is difficult to measure the transmittance of each square block in the nine area.
Action: The discussion is inserted in lines 390-393 in page 12 in the revised manuscript.
Comment 3: The reasons for the non-uniformity are from conductivity or transmittance?
Ans: As discussed in question 2, the uniformity of the transmittance for the ITO/auxiliary Au lines across the nine areas is good enough. However, the resistance of the PET/ITO film is notably high as 29.07 Ω/sq. In the revised manuscript, page 11, Fig. 9(b) shows that the OLED with Au auxiliary lines begins emitting light at 4 V, whereas the OLED without Au auxiliary lines only starts to emit at 5.5 V. The emission images of the PET/ITO OLEDs without the Au auxiliary lines, as shown in Fig. 10(a), indicate that the light first appears in the positive electrode region. This observation demonstrates that the PET/ITO anode exhibits a non-uniform current distribution at low voltage of 4 V. So the reasons for the non-uniformity are from the conductivity.
Action: Please see the discussion in lines 361-367, in page 11 in the revised manuscript.
Comment 4: The big area OLED device lifetime should be provided and discussed.
Ans: The lifetime of the large area OLED with encapsulation is approximately 4 hours. The measurement procedures were completed as quickly as possible. The initial luminance was recorded at the beginning of the tests and repeated at the end to ensure that the uniformity assessments of the nine-square-blocks were not affected by any deterioration of the OLEDs.
Action: Please see the discussions in lines 373-377, in page 11 in the revised manuscript.
Comment 5: Due to the big area OLED, how to measure the current efficiency, brighter region or dark region, it should be disclosed.
Ans: We have nine pieces of 4 cm x 4 cm paper cardboard, which function as a mask. Each piece of cardboard has a single hole for the measuring block, measuring 11.6 mm x 11.6 mm. During the measurement process, this mask is placed on top of the OLED panel. This arrangement ensures that only the brightness of one block in the nine square-blocks is measured, preventing any influence from other blocks. Only the luminance data were measured. The current efficiency was not calculated.
Action: The explanation is inserted into the revised manuscript. Please see the lines 394-399, page 12.
Comment 6: How to measure the luminance at nine area, focus on the center or others?
Ans: The explanation is the same as in Question 5. The measurement focuses on the center of each block.
Action: The explanation is inserted into the revised manuscript. Please see the lines 398-399, page 12.
Reviewer 3 Report
Comments and Suggestions for AuthorsJuang et al. introduced auxiliary electrodes to demonstrate large-area OLEDs with enhanced uniformity. The authors successfully demonstrated an OLED lighting panel with enhanced optoelectrical performance using the auxiliary Au lines. The following questions should be addressed before the publication.
1. The authors used Au in this work. It would be helpful to explain in more detail why Au is effective compared to other candidates.
2. In Figure 3, the blue OLEDs show significantly different optoelectrical characteristics depending on the thickness of HATCN. Please explain the reason behind the background.
3. In Figure 9, the device with PEDOT/au showed the lowest current density but the highest luminance among the four devices. Interestingly, the onset voltage, where the current abruptly increases, is the lowest, but the device has the lowest turn-on voltage. Please discuss these points in the revised manuscript.
Comments on the Quality of English Language
enough
Author Response
Comment 1: The authors used Au in this work. It would be helpful to explain in more detail why Au is effective compared to other candidates.
Ans: The work function of Au is about 5.1 eV, which is similar to that of ITO, at 4.9 eV. This compatibility makes them suitable for hole injection into the organic material (HATCH/TAPC). Additionally, gold can be easily deposited using a thermal evaporator.
Action: The explanation is inserted into the manuscript. Please see lines 85-88, page 2 in the revised manuscript.
Comment 2: In Figure 3, the blue OLEDs show significantly different optoelectrical characteristics depending on the thickness of HATCN. Please explain the reason behind the background.
Ans:
As the HATCN thickness increased to 7-10 nm, a decrease in current density and brightness was observed. As shown in Fig.3, the OLED with a 10 nm HATCN layer produces a lower current density of 9.14 mA/cm2 and a lower brightness of 107 cd/m2 at 9V, due to the bulk characteristics of HATCN. Excessive thickness in the HATCN layer hinder the injection of holes into TAPC, resulting in poor carrier (hole) transport characteristics. A thinner HATCN layer (3-5 nm) generally facilitates better energy alignment, allowing for easier injection of holes from the anode (ITO) into the organic layer. A thicker HATCN layer (7-10 nm) introduces additional resistance to hole injection. The energy barrier becomes more significant, resulting in a decrease in hole current. As the HATCN layer thickness increases (7-10 nm), it may exhibit more bulk characteristics, which can lead to less efficient charge transport and increased recombination losses. Excessive thickness (10 nm or more) may hinder efficient transport of holes into the subsequent TAPC layer, resulting in reduced overall carrier mobility and lower current density.
Action: The above explanation is inserted into the revised manuscript. Please see lines 162-172, page 4 in the revised manuscript.
Comment 3: In Figure 9, the device with PEDOT/Au showed the lowest current density but the highest luminance among the four devices. Interestingly, the onset voltage, where the current abruptly increases, is the lowest, but the device has the lowest turn-on voltage. Please discuss these points in the revised manuscript.
Ans:
(Q1) PEDOT/Au showed the lowest current density but the highest luminance.
The onset voltage is the “highest”. (the current abruptly increases)
-->With the addition of three-layer PEDOT:PSS, the current density decreased due to the increased resistance. The decrease in current density is attributed to the reduced hole current, as the extra PEDOT:PSS layer hinders hole injection from ITO anode, resulting in a higher onset voltage.
(Q2) the device has the lowest turn-on voltage (for luminance characteristics)
-->For the ITO/PEDOT:PSS/auxiliary Au line configuration (with a thickness of 30 nm), the luminance characteristics improved, resulting in the lowest turn-on voltage. This enhancement is attributed to the thicker auxiliary Au line, which improves the uniformity of hole current flow across the entire emitting area on the anode side, as shown in Fig. 9(b).
-->PEDOT:PSS were spin-coated three times (to get enough thickness) on the ITO/Au auxiliary lines as a planarization layer (flat layer) before HATCN evaporation to achieve adequate thickness.
Action: The above explanation is inserted into the revised manuscript. Please see lines 351-353 and 356-360, pages 10-11.
