nTOPCon

nTOPCon, short for n-type Tunnel Oxide Passivated Contact, is a passivated contact technology used in crystalline silicon solar cells. It aims to reduce rear-surface recombination while preserving high electrical conductivity, enabling higher open-circuit voltage without sacrificing current.

The typical nTOPCon stack is built on an n-type silicon wafer. The rear surface receives a thin tunnel oxide, usually about a nanometer thick, followed by a heavily doped n+ polycrystalline silicon layer. This oxide layer acts as a tunneling barrier that passivates the silicon surface, while the n+ polysilicon layer provides a low-resistivity contact to the metal electrode. The result is a highly passivated, conductive contact that transports majority carriers efficiently with reduced recombination losses.

Fabrication usually involves standard surface preparation, precise oxide growth or deposition, and subsequent deposition and dopant activation of the n+ polysilicon layer, often followed by a metal contact and grid patterning. The approach is compatible with existing silicon cell manufacturing processes and can be implemented alongside or within PERC-like architectures.

nTOPCon is part of the broader TOPCon family, which includes variants using different dopants or contact materials. Compared with conventional passivation schemes, nTOPCon devices typically exhibit higher open-circuit voltages and competitive fill factors due to reduced recombination at the rear contact, while maintaining good current collection. Challenges include ensuring uniform oxide thickness and dopant activation at scale, as well as long-term stability of the passivated interface. It remains a focus of research and development for high-efficiency silicon solar cells. See also TOPCon, p-TOPCon, HJT, and PERC.