TOPCon cell, or tunneling oxidation passivation cell, also known as i-TOPCon cell, distinguishes itself as a solar cell with a higher open circuit voltage and fill factor when compared to other cell types.
This characteristic significantly enhances the conversion efficiency of photovoltaic (PV) systems, with TOPCon cell technology achieving an impressive efficiency of 25.5%.
In comparison to other solar cell types, TOPCon cells, as passivated contact cells, exhibit a higher efficiency limit ranging from 28.2% to 28.7%. This surpasses the efficiency limits of HIT cells (27.5%) and PERC cells (24.5%). Notably, the efficiency of TOPCon cells closely approaches the theoretical limit of 29.43% for crystalline silicon solar cells.
The manufacturing process of TOPCon cell includes the following steps:
a. Manufacturing back-field: Utilizing potassium hydroxide (KOH), the process removes saw damage during the cutting of c-Si wafers. Diffusion is then employed to form a layer of boron tribromide (BBr) on the cell front.
b. Cleaning: Wet chemistry is applied to remove boron tribromide from the backside. Nitric acid and hydrofluoric acid (HF/HNO) are used to eliminate impurities, concluding with the production of an ultra-thin oxide layer through wet chemical impregnation.
c. Growth of n-a-Si layer: A phosphorus-doped amorphous silicon (n-a-Si: H) layer is grown through a plasma-enhanced chemical vapor deposition (PECVD) process. Subsequently, it is annealed at 900 ºC to convert it into an nPoly-Si layer.
d. Manufacture of P-type substrate: Silicon oxide (SiOx) or silicon nitride (SiNx), along with other materials, is employed to manufacture the P-type substrate as support for the next step of n-a-Si layer growth.
e. Growth of P-type layer: A high-quality n-a-Si layer, approximately 100-200 nm thick, is grown on the P-type substrate using an oxidation reduction method.
f. Fabrication of M Face: An electrochemical deposition process is used to create a metallic aluminum (Al) coating on the n-a-Si layer, serving as the front metal contact surface for the TOPCon cell.
g. Manufacture of Topcon cell back: Materials like water oxide (H2O) or hydroxide (OH) are applied to the back of the cell to form a transparent conductive film by applying voltage.
h. Passivation: Wet chemistry is employed to form a passive film on the back of the TOPCon cell, enhancing the solar cell’s cycle life.
i. Separation: The TOPCon cells undergo separation from the substrate, followed by thorough detection and sorting.
In summary, the intricate nine-step process of TOPCon cell manufacturing encompasses tasks such as manufacturing the back field, cleaning the wafer, growing the n-a-Si layer, manufacturing the P-type substrate, growing the P-type layer, fabricating the M-surface, manufacturing the back surface of the TOPCon cell, passivation, and separation.