A Chinese research team has fabricated ultra-narrow interconnections for organic solar modules using 355-nm ultraviolet nanosecond laser processing. The researchers claim to have achieved an interconnection width of 80 μm, which until now was only possible with femtosecond pulse lasers.
“Femtosecond pulse lasers' elevated expense and increased energy consumption may pose potential challenges, especially within large-scale manufacturing processes,” they said. “This study presents a cost-effective and reproducible approach to producing high-performance organic solar cell (OSC) modules.”
As a representative case, they chose an OSC system using an indium tin oxide (ITO) thin film layer, with zinc oxide (ZnO) as an electron transport layer. The active layer was made of the heterojunction polymer material PM6:L8-BO: PC61BM, a molybdenum oxide (MoOx) layer, and a silver (Ag) metal contact. The substrate was based on glass.
“The primary obstacle hindering the commercialization of OSCs lies in the challenge of scaling up laboratory-scale cells to large-area modules,” explained the research group. “One of the challenges involves preparing effectively interconnecting cells into modules while minimizing efficiency loss. If the large-area devices are configured as a single large cell instead of being connected in series, the restricted conductance of the transparent electrodes, such as ITO, leads to losses in series resistance, which, in turn, causes efficiency loss.”
To solve this issue, a laser scribing approach is frequently employed to create an integrated series connection using the P1-P2-P3 patterning. In their research, this scribing was done with the less-expensive nanosecond laser processing.
In the P1 stage, the ITO thin film is cut into strips that define the sub-cells. The Q pulse width is optimized at a constant of 4.0 μs. Upon investigation, the scientists found that spikes created in this process do not diminish the performance of OSC modules.
The next scribing step, the P2, “is designed to remove all layers stacked on top of the ITO layer, leaving the ITO intact and thus creating a good ohmic contact between the ITO cathode and the Ag anode.”
The scientists found that that can be created with Q-switched pulse width ranging from 4.5 to 6.6 μs, as they all demonstrated comparable results. “Increasing the Q-switched pulse width to 7.7 μs does not result in complete removal of the active layer. As a consequence, it leads to a decline in all module device parameters,” they added. “These results clearly confirm that the P2 process window can be significantly broader after finely balancing the sub-cell width and the marking depth of laser etching.”
The aim of the last step, the P3, is to segment the Ag film into separate strips for defining the sub-cells. For that, the academics applied two methods – shallow scribing (P3-S) and deep scribing (P3-D) – and found that in both cases, P3-S and P3-D, the OSC showed similar performance.
“After optimizing the laser parameters for the P1, P2, and P3 scribes, a narrow patterning area is obtained. The interconnection width is reduced to about 80 μm, which is the narrowest width using a nanosecond laser and is comparable with a femtosecond laser,” they said. “The sub-cell width is strategically set at 4.1 mm to maximize the module area and attain an impressive geometric fill factor of 98%, reaching the benchmark for nanosecond laser-manufactured OSC modules.”
Fabricating a device with an area of 1 cm2, the module yielded a power conversion efficiency of 17.55%. “An efficiency of 16.10% was obtained for an OSC module with an active area of 11.08 cm2, which is the highest efficiency for organic solar modules reported so far,” the group added. “Impressively, the top-performing OSC module achieved a remarkable geometrical fill factor of 98%, leading to a certified efficiency of 15.43% across an 11.30-cm2 aperture area.”
The novel approach was presented in “A 16.10% efficiency organic solar module with ultra-narrow interconnections fabricated via nanosecond ultraviolet laser processing,” published in Cell Reports Physical Science. The group comprised cientists from China's Central South University, the Chinese Academy of Sciences, the City University of Hong Kong, and the Chinese National Center for Nanoscience and Technology.
This content is protected by copyright and may not be reused. If you want to cooperate with us and would like to reuse some of our content, please contact: editors@pv-magazine.com.
By submitting this form you agree to pv magazine using your data for the purposes of publishing your comment.
Your personal data will only be disclosed or otherwise transmitted to third parties for the purposes of spam filtering or if this is necessary for technical maintenance of the website. Any other transfer to third parties will not take place unless this is justified on the basis of applicable data protection regulations or if pv magazine is legally obliged to do so.
You may revoke this consent at any time with effect for the future, in which case your personal data will be deleted immediately. Otherwise, your data will be deleted if pv magazine has processed your request or the purpose of data storage is fulfilled.
Further information on data privacy can be found in our Data Protection Policy.