centrotherm photovoltaics is offering a one-step PECVD aluminum axide (AlOx/SiNx) process upgrade for advanced solar cell concepts such as PERC that are applied in mono and multicrystalline cell processing. The centrotherm direct plasma process provides superior dielectric AlOx/SiNx stacks with excellent passivation properties and is said to be the fastest and easiest way to start PERC solar cell manufacturing in a cost effective way.
Problem
Driven by the pursuit of increased conversion efficiencies beyond 20%, solar cell manufacturers are necessarily turning towards more complex cell architectures for higher electrical performance. As a result, PERC technology emerged as the next generation of industrial silicon solar cells. Pre-requisite for a successful implementation is a highly efficient surface passivation of front and rear side. Aluminum Oxide (AlOx) with its excellent passivation properties and high negative fixed charge density is perfectly suited to achieve this.
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Solution
The centrotherm AlOx process shows best passivation properties at thickness < 20 nm (further reduction can be expected) also on uneven surfaces and low surface recombination velocity on p-type wafer surfaces. Furthermore, these stacks are deposited in one run and in one step, by just changing the recipe. This is an advantage compared to ALD systems where only the AlOx layer is deposited and the capping layer needs to be added in another system (mainly also by PECVD). The stack is compatible with standard Al pastes and shows a high passivation quality after contact firing.
Applications
AlOx/SiNx stack and capping layer deposition on PERC solar cell rear side for mono and multicrystalline cell processing.
Platform
For the centaurus AlOx PERC process, centrotherm uses its batch-type PECVD equipment platform, with over 900 tools installed globally. The only modification of the standard tool is the addition of a space-saving TMA cabinet, to supply gaseous N2O and TMA. By adding this hardware kit, all centrotherm PECVD systems can easily be upgraded with minimum space requirements. Compared to inline systems the centrotherm batch system offers a more than 5% abs. higher uptime and a continuous wafer flow without regular downtimes for reactor cleaning, due to no parasitic deposition in the process chamber. Even during process optimization or tube downtime the system redundancy maintains 75% of throughput on the 3 remaining tubes. The tube system is capable to manufacture stacked layers within one process, which is required for PERC applications and proven for graded layers such as AR-coatings in standard cells.
Availability
Upgrade solution ready for shipment with short delivery times.