The design was used to develop an electrode structure divided into five cells via laser scribing, with the cells bonded through electrically conductive adhesive and tested in a simulation.
“The simulation results indicated that increases in the number of cells to be divided decreased the number of fingers exhibiting the maximum efficiency,” the researchers wrote.
Fewer fingers, higher efficiency
The number of fingers optimized for division into five cells was 128, with 171 for division into three fingers. Five fingers reportedly offered power conversion efficiency of 17.346% and three, 16.855%.
“The power loss caused by the emitter resistance decreases with respect to the number of fingers, since the carrier photo-generated at the active cell area flows through a shorter distance to each finger,” the researchers said in the paper Design of a solar cell electrode for a shingled photovoltaic module application, published in Applied Surface Science and on the ScienceDirect website.
The paper also states the number of fingers showing maximum efficiency corresponded to 142 for four-cell division and 120 for six-cell division. “However, further increases in the finger number inversely decreased the efficiency because photo-current loss due to the finger shading was more dominant when compared to P-emitter loss,” added the electrode system developers.
Polycrystalline solar cells based on 6in blue wafer p type material, and exhibiting 100 fingers were produced by the research group to compare with simulation results. In the metallization phase, the electrode pattern was printed on a wafer using a mesh mask and screen printer. The front and back electrodes were fired and sintered using rapid thermal processing and the electrode was formed via contact with the silicon surface. The laser used for scribing corresponded to 10 W, with a frequency of 50 kHz, a scan rate of 1300mm/s and a repetition frequency of 30.
“We analyzed the characteristics and obtained results that were nearly similar to those of the simulation,” the paper noted, adding the characteristics were analyzed before and after division and bonding.
High-power, high-density shingled solar panels have strong rooftop PV potential. They usually feature a busbar-free structure in which only a small proportion of cells are not exposed to sunlight. The cells are bonded to form a shingled high-density string and the resulting strips are connected through a conductive adhesive. The reduced number of busbars reduces shadowing losses.
Shingled modules also require no ribbon soldering – a major cause of mechanical stress and micro-cracks.