Uncooled PV cell under variable light concentration: Determination of profiles of the temperature, the intrinsic properties and the carrier density

Abstract

Studies on concentrated light influence do not take into account the effect of the heating and this proves to be harmful on photovoltaic parameters. The main purpose of this work is to study the effects of light concentration and the heating caused by this concentration on intrinsic properties and carrier density profile. A thermal model of the PV cell is proposed. By applying the power balance at the steady-state, the PV cell thermal equation is determined. The resolution of this equation leads to temperature profile which shows a rapid increase with light concentration. The mobility n  and diffusion n D coefficients of electrons increase to reach their maxima, respectively 2 1 1 max ( ) 1895,31 n cm V s    at C=6,77 Suns where temperature is T=430,92 K and 21 max ( ) 76,55 . n D cm s   at C= 12,59 Suns where temperature is T=508,24; before decreasing. However, for the holes these parameters decrease slowly with concentration increase. Silicon gap energy decreases while electrons intrinsic density increases with increasing concentration. The variations of these parameters are explained on one hand by their dependence on temperature but also by temperature profile with concentration. An electrical model of the PV cell under variable concentration is also proposed and from which the carrier's density is determined. It emerges that the carrier density increases significantly with concentration ratio. This fact is explained by the photo-generation increase with concentration. And also, by thermal generation increase linked to temperature increases with concentration increase. Results also show that carriers density is greater in the rear side compared to the zone near the junction in opposite to authors who did not take into account temperature effect and who showed that carriers density is greater at the illuminated face.

Modeling a Water-based Concentrated Photovoltaic-Thermal (CPVT) hybrid collector: Analysis of the Influence of Mass Flow rate on Temperature and Photovoltaic Performance

“…This has been proved by Savadogo et al [7] who have shown a decrease of electron and hole mobility and diffusion coefficients with temperature rise. These authors also showed that temperature rise leads to a decrease in gap energy.…”

“…In the equations 11 and 12, τ represents the excess minority carriers (electrons) lifetime. µn,p(T) and Dn,p(T) respectively represent the mobility and diffusion coefficients of electrons and holes versus temperature [7]. It thus emerges that the diffusion coefficient and the diffusion length in the base of PV cell of the present model, respectively D c (T) and L c (T) depend on the temperature.…”

“…The rear side of the base is over-doped (p + ) in order to serve as an electronic mirror for the charge carriers photo-generated in the rear area of the base. For this reason, these PV cells are called Back-Surface-Field PV cells or B.S.F PV cells [3,7]. In the present research, the contribution of the emitter is not taken into account and we make the quasi-neutral base (QNB) hypothesis in order to neglect the crystalline electric field within the base [3,7].…”

“…For this reason, these PV cells are called Back-Surface-Field PV cells or B.S.F PV cells [3,7]. In the present research, the contribution of the emitter is not taken into account and we make the quasi-neutral base (QNB) hypothesis in order to neglect the crystalline electric field within the base [3,7]. Because of the high level of illumination, we take into account the electric field of electrons concentration gradient that prevails in the PV cell base and whose expression is given by equation 9 below [3,7].…”

“…On the other hand, the principle of light concentration leads to more rapid warming of photovoltaic panels compared to photovoltaic systems under normal and non-concentrated illumination [5,6,7,8]. Indeed, Cui Min et al [6] showed that under a light concentration ratio of 400 Suns and without a cooling aid, a PV cell temperature would rise up to 1200 • C. At this temperature, the semiconductor material would suffer irreversible damage.…”