In recent years, the market demand for N-type photovoltaic module products has been increasing rapidly. Among them, TOPCon products have taken the lead in large-scale mass production with their advantages of high cost performance and clear efficiency improvement path, and have occupied a dominant position in the global market in 2024. In the face of fierce market competition, what technical means does TOPCon battery mainly use to improve efficiency and promote cost reduction and efficiency improvement of photovoltaic systems? Sources of battery efficiency loss: optical loss and electrical loss
The efficiency loss of battery cells mainly comes from optical loss and electrical loss. Optical loss is mainly caused by the obstruction of metal grid lines on the surface of the battery; part of the electrical loss comes from the contact resistance of the metal grid lines, and the other part comes from the recombination loss of electrons and holes.
TOPCon battery: passivation contact, reducing battery recombination loss
In order to improve battery efficiency, it is necessary to continuously reduce its optical loss and electrical loss. Different battery technologies adopt different optimization measures: BC battery chooses to move all electrodes to the back of the battery cell, thereby reducing the optical loss of the front grid line obstruction; the core efficiency improvement method of TOPCon battery is to reduce the recombination loss of the battery through passivation contact technology.
In the battery, the recombination of electrons and holes mainly occurs on the surface of the silicon wafer and the part where the silicon wafer contacts the metal. After the recombination, the electrons or holes will no longer contribute to the photocurrent, thus affecting the battery efficiency.
TOPCon's passivation contact structure mainly reduces the battery recombination loss in the following three ways:
1. The tunneling effect is achieved through the deposited SiO2 film: that is, only electrons are allowed to pass through the back of the battery, while holes cannot pass through, thereby reducing the recombination loss of electrons and holes during the transmission process;
2. The field passivation effect is achieved through the deposited doped polysilicon layer (Poly-Si): that is, an electric field is formed on the surface of the battery to prevent the holes on the back from approaching and thus reduce their recombination with electrons.
3. The deposited doped polysilicon layer provides good conduction performance for electrons: the metal gate line on the back will directly contact the doped polysilicon layer, thereby avoiding direct contact between the battery silicon wafer and the metal, greatly reducing the recombination loss of this part.