Polymorphous silicon thin films produced in dusty plasmas: application to solar cells

Abstract

We summarize our current understanding of the optimization of PIN solar cells produced by plasma enhanced chemical vapour deposition from silanehydrogen mixtures. To increase the deposition rate, the discharge is operated under plasma conditions close to powder formation, where silicon nanocrystals contribute to the deposition of so-called polymorphous silicon thin films. We show that the increase in deposition rate can be achieved via an accurate control of the plasma parameters. However, this also results in a highly defective interface in the solar cells due to the bombardment of the P-layer by positively charged nanocrystals during the deposition of the I-layer. We show that decreasing the ion energy by increasing the total pressure or by using silane-helium mixtures allows us to increase both the deposition rate and the solar cells efficiency, as required for cost effective thin film photovoltaics.

Successive Generations of Dust in Complex Plasmas: A Cyclic Phenomenon in the Void Region

“…In the 2000's, a second burst of interest has been induced by potential applications of single-crystal and/or polycristalline dust particles. Indeed, single-crystal nanoparticles [8] can be incorporated in thin film layers in order to improve their mechanical and/or optoelectronical properties [9], or used for single electron device fabrication [10]. Dust forming plasmas are also used to produce analog aerosols of planet atmospheres like Titan as demonstrated by [11].…”

Probing periodic oscillations in a silane dusty plasma in a very high-frequency plasma enhanced chemical vapor deposition process

“…Nanoparticle and dust formation in a silane-hydrogen discharge in PECVD can have a beneficial or deleterious effect on the deposited layer depending on the growth conditions of silicon material. Plasma dust leads to voids and defects in the deposited layers and degrades the performance of the solar cell; incorporating silicon nanoparticles in photoactive amorphous layers, called polymorphous material, on the other hand delivers high open circuit voltage and has claimed to have better stability against light soaking [1]. Moreover, the use of a layer of silicon quantum dots in a multijunction solar cell would allow to surpass the Shockley-Queisser efficiency limit [2] by trapping light from a wider solar spectrum, while reducing losses associated with nonabsorption of below bandgap photons and lattice thermalisation loss.…”

On the heating of nano- and microparticles in process plasmas

“…Beneath treating macroscopic wafers in plasmas, also the plasma-based synthesis and modification of nanoscopic or microscopic particles (powder) with specific properties offers a variety of new applications [6][7][8][9][10][11][12][13][14], which may involve the improvement of optical or mechanical properties for coatings [9,14], for sintering processes [10], disperse composite catalysts [6] or polymorphous solar cells [7,8].…”

“…For example, Roca y Cabarrocas et.al [7] described the optimization of PIN (positive intrinsic negative) solar cells produced by plasma enhanced chemical vapor deposition from silanehydrogen mixtures. To increase the deposition rate, the discharge has been operated under plasma conditions close to powder formation, where silicon nanocrystals contribute to the deposition of so-called polymorphous silicon thin films.…”

“…decreasing the ion energy by increasing the total pressure. By using silane-helium mixtures, they were able to to increase both the deposition rate and the solar cell's efficiency, as required for cost effective thin film photovoltaics [7]. Nanoparticles produced in low-temperature plasmas are often found with crystalline structure [37], suggesting rather high particle temperatures during synthesis.…”