Reassessing the transport mechanism of TOPCon cell’s passivating contact structure

Tunneling oxide passivating contact (TOPCon) silicon solar cell has rapidly become the mainstream silicon solar cell structure in the market in the past 5 years. The featured structure of the stack of a very thin interlayer of silicon oxide and a doped polycrystalline silicon layer achieved both low contact resistivity and excellent surface passivation quality simultaneously, results in the significant improvement of open circuit voltage (Voc) and power conversion efficiency (PCE) comparing to its predecessor. It is widely believed that carriers transport through the thin oxide interlayer by quantum tunneling, while there are also proofs showing the localized pinhole on the oxide interlayer plays a role in the carrier transport. The competition between the two transport mechanisms highly depends on the oxide interlayer thickness and pinhole density, thus a generalized conclusion remains unclear. In this contribution, a direct characterization of pinhole distribution and its impact on carrier transport was made first, showing the strong dependence of carrier transport resistance to the pinhole density which is controlled by the annealing temperature. Comprehensive measurement and simulation analysis was made on the industrial completed TOPCon cell to extract the poly-bulk transport resistance. The conclusion shows that a pinhole transport dominated passivating contact can be achieved in industrial standard TOPCon cell, which provides more flexibility on process control.