[Show abstract][Hide abstract] ABSTRACT: The paper presents a review of major features of the crystalline silicon on glass (CSG) technology, its achievements, limitations and challenges, and latest developments. CSG cells are fabricated by solid-state crystallisation (SPC) of 1.5-3.5 μm thick precursor diodes prepared by PECVD or ebeam evaporation followed by thermal annealing, hydrogen passivation and metallisation. The highest efficiency of 10.4% was demonstrated on a PECVD minimodule on textured borosilicate glass. The best performing ebeam-evaporated cells on planar glass reached 8.6% efficiency. CSG cells were also produced on low-cost soda-lime glass with 8.1% and 7.1% efficiencies on PECVD and ebeam material respectively. The performance of SPC CSG cells is limited to below 11% because high defect density in SPC material limits VOC and 1.5-3.5 μm cell thickness limits JSC. A breakthrough came about when thicker poly-Si films with low defect density on glass were prepared by liquid-phase crystallisation (Amkreutz, 2011) leading to development of the next generation, liquid-phase crystallised silicon on glass (LPCSG) solar cells. The best performing LPCSG cells are made by line-focus laser crystallisation of 10 μm thick ebeam silicon films on dielectric layer coated borosilicate glass. High material quality is confirmed by low defect density observed in TEM images, high carrier mobilities, and minority carrier lifetime longer than 260 ns. An intermediate dielectric layer can be SiCx, SiOx, SiN x or their combination and its properties are crucial for cell fabrication and performance. Dopants are introduced into the LPCSG cell absorber either during film deposition or diffused from doped intermediate layer during crystallisation. Light-trapping texture is formed on the exposed silicon surface by wet etching. A cell emitter is created by diffusion from spin-on-dopant source. Cell metallisation is based on point contacts between Al and cell emitter and absorber accessed through vias etched through cell layers to different depths. LPCSG cells outperformed CSG cells, with record VOC of 585 mV and efficiency of 11.7%. Efficiencies above 13% are achievable by improving light-coupling and contacting.
Full-text · Article · Dec 2013 · Solar Energy Materials and Solar Cells
[Show abstract][Hide abstract] ABSTRACT: A variety of defect healing methods was analyzed for optimization of polycrystalline silicon (poly-Si) thin-film solar cells on glass. The films were fabricated by solid phase crystallization of amorphous silicon deposited either by plasma enhanced chemical vapor deposition (PECVD) or by electron-beam evaporation (EBE). Three different rapid thermal processing (RTP) set-ups were compared: A conventional rapid thermal annealing oven, a dual wavelength laser annealing system and a movable two sided halogen lamp oven. The two latter processes utilize focused energy input for reducing the thermal load introduced into the glass substrates and thus lead to less deformation and impurity diffusion. Analysis of the structural and electrical properties of the poly-Si thin films was performed by Suns-VOC measurements and Raman spectroscopy. 1 cm2 cells were prepared for a selection of samples and characterized by I–V-measurements. The poly-Si material quality could be extremely enhanced, resulting in increase of the open circuit voltages from about 100 mV (EBE) and 170 mV (PECVD) in the untreated case up to 480 mV after processing.
No preview · Article · May 2013 · Materials Science and Engineering B
[Show abstract][Hide abstract] ABSTRACT: Line-focus diode laser is applied to advance crystalline silicon
thin-film solar cell technology. Three new processes have been
developed: 1) defect annealing/dopant activation; 2) dopant diffusion;
3) liquid phase crystallisation of thin films. The former two processes
are applied to either create a solar cell device from pre-crystallised
films or improve its performance while reducing the maximum temperature
experienced by substrate. The later process is applied to amorphous
silicon films to obtain high crystal and electronic quality material for
thin-film solar cells with higher efficiency potential. Defect
annealing/dopant activation and dopant diffusion in a few micron thick
poly-Si films are achieved by scanning with line-focus 808 nm diode
laser beam at 15-24 kW/cm2 laser power and 2~6 ms exposure.
Temperature profile in the film during the treatment is independent from
laser power and exposure but determined by beam shape. Solar cell
open-circuit voltages of about 500 mV after such laser treatments is
similar or even higher than voltages after standard rapid-thermal
treatments while the highest temperature experienced by glass is 300C
lower. Amorphous silicon films can be melted and subsequently
liquid-phase crystallised by a single scan of line laser beam at about
20 kW/cm2 power and 10-15 ms exposure. Solar cells made of
laser-crystallised material achieve 557 mV opencircuit voltage and 8.4%
efficiency. Electronic quality of such cells is consistent with
efficiencies exceeding 13% and it is currently limited by research-level
simplified cell metallisation.
[Show abstract][Hide abstract] ABSTRACT: Crystalline silicon on glass (CSG) is a polycrystalline silicon PV technology that enables low cost PV manufacturing as it combines the use of less than 2µm of crystalline silicon and single-panel, large-scale manufacturing. The active material is deposited as amorphous silicon on glass by plasma enhanced chemical vapour deposition (PECVD) using a tool developed for the flat panel display industry. Until now, little has been revealed about the process used for silicon deposition for CSG modules. This report will review aspects of the process optimisation of pilot line depositions describing the impact of deposition rate, thickness and base doping on efficiencies between 8 and 9%. Changes in the deposition process resulted in improvements in the material quality. With changes in the device structure to exploit the better material, the efficiency of CSG modules produced was improved from below 8% to 8.8%. With the application of a high-density contact scheme with lower resistance losses, the efficiency of the 95 cm 2 aperture area modules was improved to over 9%.
[Show abstract][Hide abstract] ABSTRACT: CSG Solar has developed a unique thin-film, crystalline silicon on glass (CSG) technology to the point of readiness for large-scale manufacture. Effective, low-cost defect passivation is critical to the commercial viability of this technology. A rapid, high-temperature, remote-plasma hydrogenation method has been developed that quadruples CSG module efficiency to more than 8% whilst being compatible with low-cost manufacturing. The hydrogenation method is described, the improvement it gives to CSG modules is characterised, and cost projections for factory-scale hydrogenation are presented.
[Show abstract][Hide abstract] ABSTRACT: Crystalline silicon on glass (CSG) solar cell technology was developed to address the difficulty that silicon wafer-based technology has in reaching the very low costs required for large-scale photovoltaic applications as well as the perceived fundamental difficulties with other thin-film technologies. The aim was to combine the advantages of standard silicon wafer-based technology, namely ruggedness, durability, good electronic properties and environmental soundness with the advantages of thin-films, specifically low material use, large monolithic construction and a desirable glass superstrate configuration. The challenge has been to match the different preferred processing temperatures of silicon and glass and to obtain strong solar absorption in notoriously weakly-absorbing silicon of only 1.4 μm thickness, the thinnest active layer of the key thin-film contenders. A rugged, durable silicon thin-film technology has been developed arguably with the lowest likely manufacturing cost of these contenders and confirmed efficiency for small pilot line modules already in the 8–9% energy conversion efficiency range, on the path to 12–13%.