TOPCon Vs HJT : A Status Quo

TOPCon (Tunnel Oxide Passivated Contacts) has become the forefront winner in solar cell manufacturing and became extremely successful with 700GW of capacity in China alone by December 2023, while HJT (Heterojunction Technology) which was supposed to compete it, has not crossed beyond 40GW capacity. HJT capacities are still in Pilot phase with no clear deadline on when it can achieve cost parity with TOPCon. Although the innovative ideas like Copper coated silver metallization and extreme thinner wafers (<100μm) are still in trials, the manufacturability (in terms of reliability, cost reduction and high volume capabilities) are still debatable & dubious.

HJT, although it can claim with very less number of process steps, could not possibly compete in both CAPEX & OPEX in comparison with well-established TOPCon process and seemed to be a major show stopper. In both HJT & TOPCon, PECVD processes have become inevitable, but the PECVD technology, which is used seemed to be different. A decade ago, many European manufacturers were focussing on Indirect Plasma or Remote plasma for silicon nitride (Si3N4 deposition for Anti-reflection coating) for Multicrystalline solar cells with a scientific reasoning that remote plasma damage will be extremely less and can be more helpful in improving the efficiency compared to direct plasma, where surface damage was substantial. However, due to annealing processes involved in PECVD & fast firing process, this effect was not pronounced, and no difference in efficiency was visible between direct & indirect plasma technologies. The CAPEX & OPEX cost of indirect plasma technologies were higher compared to direct plasma technologies and thus for both, Multi & PERC technologies, direct plasma tools became mainstream.

In the case of HJT being a surface sensitive process, scientists brought in indirect plasma technologies back with a hope that they can beat TOPCon efficiencies. Unfortunately, this has not happened till date. Copper coated silver is a great weapon to reduce the overall silver usage and to bring down the cost drastically, but with copper being the core and silver being the shell, the precise manufacturability of core-shell in nanoscale dimensions are still unimaginable and subsequent to that, the reliability (peel strength, field data) are far from reality, which can offer warranty for 25-30+ Years in outdoor conditions. However, if this really happens in reality, this can be a great break through.

The second pertinent issue seems to the replacement for ITO (to replace Indium), which many people claimed are AZO, etc, but none of these solutions were permanent.

The third issue seems to be moving from a-Si to multicrystalline to nanocrystalline silicon deposition and within which many types of CVDs compete to prove its capability and there is no proven unified technology, which confuses many manufacturers as well.

The HJT route was initially favoured thinking that when technology move towards Tandem, the integration with Perovskites (too much hyped technology in solar industry) will be one stop solution. However, TOPCon counterparts also came-up with integration option with Perovksites, if it ever happens in real life and if ever Tandem would be mass manufactured. So, the very thought of having preferential bias towards HJT route doesn’t exists as well.

With current upgrades from TOPCon like introducing LECO (laser enhanced contact optimization) and Bi-Poly or double Poly processes, TOPCon is proving it’s capability once again and is expected to reach 26%+ efficiency in mass cell manufacturing to help manufacturers worldwide with better costing and a reliable product.