Back Surface Recombination Velocity Dependent of Absorption Coefficient as Applied to Determine Base Optimum Thickness of an n+/p/p+ Silicon Solar Cell

Abstract

The monochromatic absorption coefficient of silicon, inducing the light penetration depth into the base of the solar cell, is used to determine the optimum thickness necessary for the production of a large photocurrent. The absorption-generation-diffusion and recombination (bulk and surface) phenomena are taken into account in the excess minority carrier continuity equation. The solution of this equation gives the photocurrent according to absorption and electronic parameters. Then from the obtained short circuit photocurrent expression, excess minority carrier back surface recombination velocity is determined, function of the monochromatic absorption coefficient at a given wavelength. This latter plotted versus base thickness yields the optimum thickness of an n + -p-p + solar cell, for each wavelength, which is in the range close to the energy band gap of the silicon material. This study provides a tool for improvement solar cell manufacture processes, through the mathematical relationship obtained from the thickness limit according to the absorption coefficient that allows base width optimization.

Back Illuminated N/P/P<sup>+</sup> Bifacial Silicon Solar Cell under Modulated Short-Wavelength: Determination of Base Optimum Thickness

“…In addition, the generation of carriers by a strong absorption (large α(λ)) of the incident flow in the rear face [8] [10] [21] hence the need to reduce the distance to be covered (closer junction and back face), in order to collect the maximum carriers. Other works corroborate our results, showing the decrease in the optimum thickness of the silicon solar cell base, when subjected to: Monochromatic light with a constant flow of absorption coefficient (α(λ)) [56] Monochromatic light α(λ) in frequency modulation (ω) [58] Constant magnetic field B [66] Flow of charged particles [67] Change in the doping rate [60].…”

“…Thus the determination of phenomelogical parameters [56] [57] in the solar cell, through theoretical and experimental studies, allows to trace the performance of photoconversion. In previous works the solar cell is considered in static or dynamic mode (frequency) [58] [59].…”

Diffusion Coefficient at Resonance Frequency as Applied to n+/p/p+ Silicon Solar Cell Optimum Base Thickness Determination

“…• the spectral composition of light (monochromatic [49] [56] or polychromatic [63]) having a constant incident photons flux or in frequency modulation • the mode of illumination that can be, perpendicular to the junction (by the front [64] or by the back side [49]) or parallel to the junction (Vertical Mutijunctions) [57] [62] [65] These two types of parameters influence the technique of determining the optimum thickness of the base, taking into account the optoelectronic factors.…”

Optimisation de l’épaisseur de la base de taux de dopage (Nb) de la photopile (n+/p/p+) au silicium à multi jonctions verticales connectées en série et placée sous éclairement monochromatique en modulation de frequence

“…Les figures (10, 11 et 12), montrent la technique [9,12,20,36,38,39] d'intersection des courbes des vitesses de recombinaison des porteurs minoritaires en face arrière, représentées en fonction de la profondeur (H) de de la base, pour les différentes régions de frequence de modulation. Les tableaux (1, 2, 3) donnent les résultats respectifs obtenus de l'épaisseur optimum (Hopt) de la base de la photopile sous différents taux de dopage et pour les trois domaines de fréquences.…”

“…Dans cet intervalle de basses fréquences, le temps de relaxation des porteurs minoritaires est important (grandes valeurs de D dans Eq. 5 et 11), permettant une grande distance de parcours (relation d'Einstein), alors une grande épaisseur optimum de la base est obtenue [12,20,34,38,40] .…”