Laser Processing and Rapid Thermal Annealing of High-Efficiency c-Si Photovoltaic Devices

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Sinha, Arpan, Electrical Engineering - School of Engineering and Applied Science, University of Virginia
Gupta, Mool, EN-Elec & Comp Engr Dept, University of Virginia

Recent developments in the c-Si photovoltaic (PV) solar cells based on inter-digitated back-contact heterojunctions (IBC-HJ) and carrier selective layers have resulted in record power conversion efficiencies. Multiple photolithography steps, high-temperature masked deposition, and furnace annealing are employed to fabricate these high-efficiency devices. Unfortunately, such conventional methods increase the thermal budget and technical complexity, affecting the levelized cost.
This thesis describes a comprehensive scientific investigation of laser processing and rapid thermal annealing (RTA) in improving solar cell device performance and circumventing the limitations of conventional fabrication methods. Different materials, optical, and electrical characterization techniques were employed to support the scientific investigations.
This work has investigated: (1) the selective laser ablation of top sacrificial a-Si:H layers without damaging underneath the passivation layer in IBC-HJ solar cell, (2) the use of RTA under different temperatures and atmosphere for B-doped p-TOPCon solar cell fabrication, (3) the effects of RTA thermal and cooling cycles on the passivation quality in B-doped p-TOPCon solar cells, (4) the thermal annealing behavior of transition metal oxide based PV devices, and (5) the use of laser heat for selective KOH etching of Si without any laser-induced damages.
The main results are (1) the achievement of high carrier lifetime and open circuit voltage after optimized nanosecond pulsed laser ablation, (2) the use of Essential MacLeod simulated color charts to determine the laser ablation depth accurately, (3) the effect of RTA treatment on the reduction in the hydrogen-induced blister formation, enhancement of the passivation quality, increased dopant activation and effect of SiNx capping layer on B-doped p-TOPCon PV devices, (4) Optimized longer cooling times to achieve good passivation quality and dopant activation in B-doped p-TOPCon solar cells, (5) the optimization of ALD Al2O3, TiOx and PVD MoOx and successful laser annealing to fabricate bifacial TMO-based CSPC solar cells, and (6) the feasibility of selective laser-assisted chemical etching using a μs-pulsed laser to create patterns on Si surface without any laser-induced defects and has potential applications in a wide variety of Si devices.
This work shows the successful implementation and limitations of laser processing and RTA in fabricating high-efficiency silicon photovoltaic devices. A fundamental understanding of the laser material interaction and RTA in high-efficiency silicon photovoltaic devices is provided. Both IBC-HJ and TOPCon c-Si devices are expected to dominate the future photovoltaic market, so the presented results will be helpful in the advancement of both technologies.

PHD (Doctor of Philosophy)
Laser processing, Rapid thermal anneal, Silicon solar cells, IBC-HJ, TOPCon, Boron doped, Thin film deposition, TMO, Carrier selective passivated contacts, Optical simulation, Characterization, Process development and optimization, Photovoltaics
Sponsoring Agency:
NASA Langley Professor ProgramNSF I/UCRC program grant No. 1338917NSF ECCS grant No. 2005098DOE award No. DE- EE0007534
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