Carsten Demberger

Investigation of the Internal Back Reflectance of Rear-Side Dielectric Stacks for c-Si Solar Cells

This paper addresses the calculation of internal back reflectance for various dielectrics that are used in rear-side passivated crystalline silicon solar cells. Optical modeling of various stack configurations is examined to explore the back-surface reflectance at the Si-dielectric interface for different film combinations and thicknesses as a function of wavelength and internal angle of incidence at the rear side. Specifically, configurations using aluminum oxide (AlOx), silicon nitride (SiNx), titanium dioxide (TiO2), and silicon dioxide (SiO2) were investigated with a focus on designing stack configurations that will also allow for high-quality passivation and are compatible with a high-volume manufacturing environment. In addition, samples were fabricated by plasma-enhanced and atmospheric pressure chemical vapor deposition of thin dielectric films onto polished and textured monocrystalline silicon wafers. Spectral reflectance curves of the samples are presented to supplement and validate the conclusions that are obtained from the optical modeling data.

Co-diffused APCVD boron rear emitter with selectively etched-back FSF for industrial N-type Si solar cells

The employment of a B-doped atmospheric pressure chemical vapor deposited (inline belt APCVD) borosilicate glass is an elegant technology for industrially realizing a p emitter. By drive-in of B and a subsequent POCl3 co-diffusion, p emitter and n front surface field (FSF) are established in a single process step. APCVD-SiOx is used to prevent the p emitter from being compensated during P diffusion. Its thickness needs to be adapted in order not to affect the p profile during POCl3 diffusion while keeping it removable. For rear junction solar cells, it is crucial to ensure low recombination activity at the front. Therefore, a selectively etched-back FSF is to be established in the solar cell. An adjusted etch-back solution increases n Rsheet successively and well controllably, accompanied by a drastic j0FSF reduction while simultaneously almost completely maintaining p Rsheet. A 43 /sq APCVD-AlOx passivated p emitter achieves j0E of only 52 fA/cm. Total implied VOC of a pseudo solar cell structure attains up to 695 mV. The newly developed APCVD p emitter combined with the co-diffused and selectively etched-back FSF employed in an industrial n-type solar cell achieves 18.8% efficiency in a first experiment being still limited by a poor Ag/Al contact to the B-emitter.

Fast illuminated Lock-In Thermography: An inline shunt detection measurement tool

This paper focuses on the fast spatially resolved detection of material and / or processing induced shunting using fast illuminated Lock-In Thermography (iLIT). With this technique shunting can be detected spatially resolved within a measurement time of only 1 s and thus the method in principle can be used for inline characterisation. Points addressed are the influence of Lock-In frequency on spatial resolution and the effect of a lowered illumination intensity for a better selectivity between shunting and recombination induced generation of heat. The method is tested for different common sources of shunting in standard industrial-type solar cells (points like shunts, cracks, poor edge isolation, contaminations) and all major types of shunts under investigation can be detected in times relevant for inline characterisation.

Phosphorous Doping from APCVD Deposited PSG

The phosphorous diffusion from atmospheric pressure chemical vapor deposition (APCVD) deposited phosphorus silicate glass (PSG) promises reduced process costs compared to the standard POCl3 diffusion process, since no POCl3 gas flow is necessary during the diffusion process. Therefore, much smaller or no spacing between the wafers is necessary and the throughput of the diffusion process can be significantly increased. Furthermore, it allows a structuring of the doping source prior to diffusion. We investigate the effect of basic process parameters concerning the deposition of the PSG and the capping layer on sheet resistance and uniformity. On standard aluminum back surface field (Al-BSF) solar cells, cell efficiencies of up to 19.6 % were achieved. In a high temperature co-diffusion process with reduced P content, the APCVD-PSG emitter passivated with fired PECVD-SiNX features low j0E of 100 fA/cm2 at 50 Ω/sq. This results in a high cell VOC of 639 mV while leading to a jSC loss due to increased Auger recombination in the deep emitter profile. This loss can partly be compensated by a selective emitter etch-back. It would not occur, when the doping profile is located at the rear side of a bifacial or back contact solar cell as a BSF.