TOPCon Technology Introduction

1. Overview

TOPCon (Tunnel Oxide Passivated Contact) is a high-efficiency passivated contact technology based on an N‑type silicon substrate. First reported by the Fraunhofer Institute in 2013, it introduces an ultra‑thin tunnel oxide layer and a doped polysilicon layer on the rear side, significantly reducing metal contact recombination and greatly improving conversion efficiency.

2. Core Structure & Working Principle

Structure: N‑type silicon wafer + front boron‑diffused emitter + rear tunnel oxide (~1.5 nm) / doped polysilicon layer (100–200 nm)

Principle: The ultra‑thin oxide layer allows majority carrier electrons to tunnel into the polysilicon layer while blocking minority carrier holes, achieving full‑area passivated contact without laser opening.

3. Key Fabrication Processes

Mainstream approach: LPCVD (Low‑Pressure Chemical Vapor Deposition) – most mature for mass production, but suffers from wrap‑around deposition.

Alternative approaches: PECVD (in‑situ doping, no quartz tube consumables), PVD (no wrap‑around, but uniformity challenges).

PERC compatibility: Highly compatible – can be built on existing PERC lines by adding a few steps (boron diffusion, tunnel oxide deposition, polysilicon deposition), with low retrofitting cost.

4. Technical Advantages

High efficiency: Theoretical limit 28.7% (double‑side) / 27.1% (single‑side); mass‑production efficiency 24–25.5%; lab record >26.6%

High bifaciality: >85%, better than PERC (~75%)

Low temperature coefficient: –0.30%/℃, outperforms PERC (–0.35%/℃) under high temperature

Low degradation: No boron‑oxygen defect in N‑type wafers; first‑year degradation ~1%, linear degradation ~0.4%

Excellent low‑light response: Superior power generation during mornings, evenings, and cloudy conditions

5. Quick Comparison: PERC vs TOPCon vs HJT

6. Future Development Trends

Continuous efficiency improvement: double‑side passivation, poly‑thinning, edge passivation, SE laser doping – potential gain of 0.2–0.4% absolute.

Evolution to TBC: TOPCon + back‑contact structure (TBC) is regarded as the next‑generation mainstream technology.

Perovskite tandem: TOPCon/perovskite tandem has a theoretical efficiency >40%; certified cell efficiency of 34.82% has been achieved; GW‑scale production expected around 2027–2028.

Summary: TOPCon has become the dominant N‑type solar cell technology thanks to its high efficiency, low cost, and excellent compatibility with existing PERC lines. Its clear roadmap for further efficiency gains and potential evolution to TBC and tandem structures will keep it at the forefront of the PV industry for the next 5–10 years.