Investigation of the emitter band gap widening of heterojunction solar cells by use of hydrogenated amorphous carbon silicon alloys

Abstract

The hydrogenated amorphous carbon-silicon alloys [a-SixC1−x(n):Hy] and [a-Six(n):Hy] layers were investigated in order to prove the feasibility to widen the optical band gap in emitters of the heterojunction solar cells. The alloys were fabricated by decomposition of silane (SiH4), phosphine (PH3), methane (CH4), and hydrogen (H2), using a plasma enhanced chemical vapor deposition. Particularly, we focused on the incorporation of hydrogen and carbon within the resulting [a-SixC1−x(n):Hy] and [a-Six(n):Hy] films, which later form the emitter. The corresponding local vibrational modes of Si−Hx, C−H, and the corresponding network have been analyzed by μ-Raman spectroscopy. The addition of carbon degrades the photoelectronic properties in the emitter layer. This deterioration can be minimized by H dilution. The resulting optical band gap EG as well as the thickness of the emitter were determined by spectroscopic ellipsometry. It was confirmed that the band gap EG can be tailored by using an appropriate gas mixture during the decomposition. Furthermore, we analyzed the I−V characteristics of the prepared heterojunction solar cells. A trade-off between the electrical defects density and the optical losses induced an improvement of the I−V characteristics with increasing carbon and hydrogen concentration in the feedstock during the deposition.

Band gap optimization of the window layer in silicon heterojunction solar cells

“…(10), V OC depends on the effective interface recombination velocity. And it is apparently independent on the band gap of the window layer, E g2 , which seems to contradict with the results reported by Mueller et al (2007).…”

“…And the properties of silicon heterojunction solar cells differ with the band gap of the window layer. It is reported (Mueller et al, 2007) http://dx.doi.org/10.1016/j.solener.2014.08.010 0038-092X/Ó 2014 Elsevier Ltd. All rights reserved. that a certain amount of carbon and hydrogen, which widens the band gap of the a-Si layers, increases the open circuit voltage as well as the short circuit current.…”

“…With the development of the thin film deposition technique, various silicon thin films, such as a-Si:H, microcrystallite silicon (uc-Si:H), silicon carbide (a-SiC x :H), nanometer hydrogenated silicon (ncSi:H) and polymorphous silicon (pm-Si:H), have been deposited as the window layer (namely the emitter) of silicon heterojunction solar cells (Kim et al, 2008;Ling et al, 2012;Mueller et al, 2007;Page et al, 2011;Yamamoto et al, 2002;Wu et al, 2009;Hamashita et al, 2012). The combination of silicon thin films with crystalline silicon is one of the most promising solar cells.…”

High-efficiency Silicon Heterojunction Solar Cells: A Review

“…For SHJ devices, such films should not jeopardize surface passivation and emitter formation. Tested alternatives to replace the a-Si:H stacks are (microcrystalline) silicon oxides [136,137,182,183] and carbides [148,[184][185][186]. Microcrystalline silicon has a lower but indirect bandgap and features a higher doping efficiency, making it an attractive material for emitter [52,[187][188][189][190] and BSF formation [189,[191][192][193] as well.…”

On scaling laws of biosensors: A stochastic approach

“…However, when the concentration of interfering species is much higher than the concentration of the target analyte ͑e.g., in the case of low-expressed genes in DNA microarrays with complex biological background͒, nonspecific binding can dominate the measured signal and hence limit the minimum detectable level ͑MDL͒. [10][11][12][13] It is widely recognized that although the MDL is fundamentally noise and interference limited in all biosensors, the highest detection level ͑HDL͒ is limited by the capturing probe density and the associated saturation level ͑see Fig. 1͒.…”