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

Abstract

A bifacial silicon solar cell under monochromatic illumination in frequency modulation by the rear side is being studied for the optimization of base thickness. The density of photogenerated carriers in the base is obtained by resolution of the continuity equation, with the help of boundary conditions at the junction surface (n + /p) and the rear face (p/p + ) of the base. For a short wavelength corresponding to a high absorption coefficient, the AC photocurrent density is calculated and represented according to the excess minority carrier's recombination velocity at the junction, for different modulation frequency values. The expression of the AC recombination velocity of excess minority carriers at the rear surface of the base of the solar cell is then deduced, depending on both, the absorption coefficient of the silicon material and the thickness of the base. Compared to the intrinsic AC recombination velocity, the optimal thickness is extracted and modeled in a mathematical relationship, as a decreasing function of the modulated frequency of back illumination. Thus under these operating conditions, a maximum short-circuit photocurrent is obtained and a low-cost bifacial solar cell can be achieved by reducing material (Si) to elaborate the base thickness.

Optimization of the thickness of the doping rate base (Nb) of the (n+/p/p+) silicon solar cell with vertical multi-junctions connected in series and placed under monochromatic illumination in frequency modulation

“…3). It is the same with the effect of the doping rate [36,37 ] which reduces the amplitude of the maximum of the density of the minority charge carriers and its displacement towards the junction, when Nb increases. For Sf greater than 10 4 𝑐𝑚/𝑠 the dynamic photocurrent density modulus (Fig.…”

“…7 and 8) corresponds to the short-circuit current density, which decreases slightly with the doping rate at low modulation frequencies. On the other hand, at high modulation frequencies, the amplitude of the short-circuit current density increases more drastically with the doping rate [36,37] because the maximum density of charge minority carriers shifts towards the junction, when Nb increases.…”

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

“…3). Il en est de même avec l'effet du taux dopage [36,37] qui réduit l'amplitude du maximum de la densité des porteurs minoritaires de charge et son déplacement vers la jonction, lorsque Nb croît.…”

“…7 et 8), correspond à la densité de courant de court-circuit, qui décroit légèrement avec le taux de dopage aux faibles fréquences de modulation. Par contre aux grandes fréquences de modulation, l'amplitude de la densité du courant de court-circuit augmente de façon plus drastique avec le taux de dopage [36,37] parce que le maximum de la densité des porteurs minoritaires de charge se déplace vers la jonction, lorsque Nb croît.…”

“…Le taux de dopage [6,22,33,37] de la base de la photopile influence sur sa performance, par la création des porteurs minoritaires de charge en excès, et sur l'épaisseur optimum [36] de la base. En effet l'épaisseur décroit avec le coefficient de diffusion optimum et par conséquent avec l'augmentation du taux de dopage (Eqs.…”