Liquid Phase Crystallization LPC
For liquid phase crystallization (LPC) nano-crystalline silicon is deposited on glass substrates and subsequently crystallized by a line-shaped energy source. A laser beam scans the sample with a velocity of 3 mm/s and locally melts the silicon. It recrystallizes polycrystalline into grains that are up to a few centimeters in length and a couple of millimeters in width. With this technique not only a morphology comparable to multi-crystalline silicon wafer solar cells are achieved but also similarly high open-circuit voltages [1,2].
In case a textured glass substrate is used for enhancing light in-coupling into the solar cell, the silicon grows conformally on the textured substrate resulting in a double-sided textured absorber layer. If the rear side texture is protected by a sacrificial capping layer during crystallization the double-side texture is preserved even after crystallization. Hence, it provides not only enhanced light in-coupling properties at the front side but also light scattering properties at rear side trapping the light within the absorber layer [3,4].
Double-sided textured liquid phase crystallized silicon thin-films on a square lattice texture with a period of 2 µm. (a) Schematic during liquid phase crystallization. (b) Cross sectional scanning electron microscopy image, here with a 6 µm thick silicon layer.
The challenge to face is to maintain the high electronic material quality of the silicon despite it being grown and crystallized on a rough substrate. The goal is to find an optimum balance between optical and electronic gain in order to maximize the solar cell efficiency [5–7].
Photograph of a double-sided textured silicon thin-film solar cell and scanning electron microscopy image of the underlying hexagonal sinusoidal texture with a period of 750 nm. Due to texturing the light path inside the solar cells is alternated and the samples shimmer colorfully under oblique incidence of light.
References
- [1] J. Haschke, D. Amkreutz, L. Korte, F. Ruske, and B. Rech, “Towards wafer quality crystalline silicon thin-film solar cells on glass,” Sol. Energy Mater. Sol. Cells, vol. 128, pp. 190–197, 2014.
- [2] C. Thi Trinh, N. Preissler, P. Sonntag, M. Muske, K. Jäger, M. Trahms, R. Schlatmann, B. Rech, and D. Amkreutz, “Potential of Interdigitated Back-Contact Silicon Heterojunction Solar Cells for LIquid Phase Crystallized Silicon on Glass with Efficiency above 14 %,” Sol. Energy Mater. Sol. Cells, vol. 174, no. June 2017, pp. 187–195, 2017.
- [3] C. Becker, D. Amkreutz, T. Sontheimer, V. Preidel, D. Lockau, J. Haschke, L. Jogschies, C. Klimm, J. J. Merkel, P. Plocica, S. Steffens, and B. Rech, “Polycrystalline silicon thin-film solar cells: Status and perspectives,” Sol. Energy Mater. Sol. Cells, vol. 119, pp. 112–123, Dec. 2013.
- [4] C. Becker, V. Preidel, D. Amkreutz, J. Haschke, and B. Rech, “Double-side textured liquid phase crystallized silicon thin-film solar cells on imprinted glass,” Sol. Energy Mater. Sol. Cells, vol. 135, pp. 2–7, Apr. 2015.
- [5] V. Preidel, D. Amkreutz, J. Haschke, M. Wollgarten, B. Rech, and C. Becker, “Balance of optical, structural, and electrical properties of textured liquid phase crystallized Si solar cells,” J. Appl. Phys., vol. 117, no. 22, p. 225306, Jun. 2015.
- [6] G. Köppel, B. Rech, and C. Becker, “Sinusoidal nanotextures for light management in silicon thin-film solar cells,” Nanoscale, vol. 8, no. 16, pp. 8722–8728, 2016.
- [7] D. Eisenhauer, G. Köppel, K. Jäger, D. Chen, O. Shargaieva, P. Sonntag, D. Amkreutz, B. Rech, and C. Becker, “Smooth anti-reflective three-dimensional textures for liquid phase crystallized silicon thin-film solar cells on glass,” Sci. Rep., vol. 7, no. 1, p. 2658, Dec. 2017.
