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A new Chinese study shows that ultra-tight interconnects can significantly improve the performance of organic photovoltaic modules. Scientists built a 11.08 cm2 panel with an impressive geometric fill factor of 98%.
A Chinese research team has fabricated ultra-narrow interconnects for organic solar modules using 355nm ultraviolet laser processing in nanoseconds. The researchers claim to have achieved an interconnect width of 80 µm, something previously only possible with femtosecond pulsed lasers.
“The high cost and higher energy consumption of femtosecond pulse lasers can pose potential problems, especially in large-scale manufacturing processes,” they say. “This study presents a cost-effective and reproducible approach to produce high-performance organic solar cell (OSC) modules.”
As a representative case, they chose an OSC system using a thin layer of indium tin oxide (ITO), with zinc oxide (ZnO) as the 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 made of glass.
“The main obstacle hindering the commercialization of OSCs is the difficulty of converting laboratory-scale cells into large-area modules,” the research group explains. “One challenge is to efficiently arrange the interconnection of cells into modules while minimizing efficiency loss. If large-area devices are configured as a single large cell instead of connected in series, the restricted conductance of transparent electrodes such as ITO leads to losses in series resistance, which in turn cause efficiency losses.”
To solve this problem, a laser scribing method is often used to create an integrated serial connection using the P1-P2-P3 pattern. In their research, this scribing was done using the less expensive nanosecond laser processing.
In the P1 stage, the thin ITO film is cut into strips that define the subcells. The Q pulse width is optimized to a constant of 4.0 µs. Upon investigation, the scientists found that the spikes created in this process do not decrease the performance of the OSC modules.
The next scratching step, P2, “is designed to remove all the layers stacked on top of the ITO layer, leaving the ITO intact and thus creating good ohmic contact between the ITO cathode and the Ag anode.”
The scientists found that this can be achieved with a 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. Consequently, it causes a decrease in all device parameters of the module,” they added. “These results clearly confirm that the P2 process window can be significantly wider after finely balancing the subcell width and marking depth of the laser etching.”
The aim of the last step, P3, is to segment the Ag film into separate strips to define the subcells. To do this, the researchers 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 scribing patterns, a narrow scribing area is achieved. The interconnect width is reduced to about 80 µm, which is the narrowest width using a nanosecond laser and comparable to that of a femtosecond laser,” they noted. “The subcell width is strategically set at 4.1 mm to maximize the module area and achieve an impressive geometric fill factor of 98%, reaching the benchmark for OSC modules fabricated using nanosecond lasers.”
By fabricating a device with a surface area of ??1 cm2, the module achieved a power conversion efficiency of 17.55%. “An efficiency of 16.10% was achieved for an OSC module with an active area of ??11.08 cm2, which is the highest efficiency for organic solar modules recorded to date,” the group added. “Impressively, the highest-performing OSC module achieved a remarkable geometric fill factor of 98%, leading to a certified efficiency of 15.43% in an aperture area of ??11.30 cm2.”
The novel method 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 consisted of scientists from Central South University of China, the Chinese Academy of Sciences, the City University of Hong Kong, and the China National Center for Nanoscience and Technology. |
