In the last years, PV manufacturing has seen a shift from Al-BSF (Back Surface Field) to PERC (Passivated Emitter and Rear Contact) solar cells to drive down the recombination current at the rear surface of the cells. Other shifts, e.g. transition from multicrystalline to monocrystalline material and from p-type to n-type base doping, are also taking place to minimize recombination currents in the bulk of the device. This evolution, combined with the advantages of using bifacial devices (energy contribution by rear illumination), is expected to lead to an increased market share of n-type bifacial PERT (Passivated Emitter and Rear Totally diffused) devices. The weakest point of these devices is the recombination at the interface between the silicon wafer and the metal contact. This problem can be mitigated using passivated contacts, shielding the minority carriers in the silicon wafer from the recombination centers at the metal contact while allowing fluent transport of the majority carriers to the same contacts.
The focus of this PhD will be on the development and in-depth characterization of poly-Si based passivated contacts for bifacial nPERT cells in combination with next-generation metallization methods. Part of the work will concentrate on optimizing the specs of the tunnel oxide in between the silicon bulk and the poly-Si layer while the largest task will be the optimization of the poly-Si layers itself (thickness, doping,...) to achieve a recombination current as low as possible. The impact of next-generation metallization techniques based on plating and other necessary process techniques (lasering, dielectric deposition, annealing) needs to be considered. Application and analysis of standard screenprinted metallization on the developed poly-Si structures will serve as reference. Initial implementation of the poly-Si layer will be at the rear of a bifacial solar cell followed by feasibility study for integration at the front surface of these devices either as blanket or, more likely, local application at the contact site.
Experimental tests during this PhD will be conducted on both specialized test structures and complete solar cell devices using equipment available in imec’s state-of-the-art R&D solar cell line. This PhD thesis will make use of advanced characterization tools (examples: photoluminescence, spectral response, current-voltage measurements,...) and material analysis techniques (examples: scanning electron microscopy, energy dispersive spectroscopy, x-ray fluorescence) available at imec. This research will also use analytical modeling tools to support the experimental observations.
Required background: specialization in microelectronics or silicon photovoltaics is an important plus
Type of work: 10% literature study, 60% experimental, 30% characterization and modeling
Supervisor: Jef Poortmans
Daily advisor: Maria Recaman-Payo
The reference code for this PhD position is SE1712-18. Mention this reference code on your application form.