Influence of temperature on effective value of a current density of a semiconductor solar cell is investigated. New equations for explanation of dependence of photovoltaic characteristics of solar cell from temperature are received.
The semiconductor photo-electric power takes a perspective place among set of renewable energy. Thus on a way of wide application of solar cells (SC) in power supply programs, there are some problems. Most considerable of them are the high cost price of solar energy and low efficiency of SC [
Semiconductor SC with high cost can be used without an exception in various special conditions. For example, at their use as an energy source of space flying devices, they are exposed to essential cooling [
Now is spent theoretical and experimental researches influence of ambient temperature on the cores Photovoltaic parameters of SC [
Influence of ambient temperature and, hence, the most SC on its photovoltaic characteristics and efficiency of photoelectric conversation by semiconductor structures is the most important object of experimental and theoretical research. It is known that one of the basic photovoltaic characteristics of SC, defining efficiency of conversation of solar energy is effective power which is traditionally expressed by formula [
P m = j m U m (1)
where Jm and Um are maximum (effective) values of according to photocurrent density and voltage.
Experimental results show that Jm and Um are depends on temperature. But in the scientific literature the expressions allowing preliminary to define these dependence almost are not presented.
Therefore in this work the results, the research conducted by us by a semi-empiric method definition of dependence of effective value of Jm and Um from temperature are stated.
On
As it is known the equation for a straight line which is passing through two points has the following appearance
j − j 1 j 2 − j 1 = U − U 1 U 2 − U 1 (2)
From this Equation (2) it is possible to receive for a 1-straight line (
j = − j s c U o c U + j s c (3)
It is visible that the angular factor of this straight line matters a = − j s c U o c . For a 2-straight line also looks like j = a U + b . As, the 2-straight line is a tangent to I - V, therefore angular factor of this line it is possible to define from I - V:
j p h = j 0 ( exp ( e U n k T ) − 1 ) − j s c (4)
where jph―photocurrent density, j0―density of a saturation current, e―a electron charge, k―constant of Boltzmann, T―temperature.
It is known that value of factor not idealities (n) of SC I - V is define by type of an electric current [
a = j ′ p h ( U m ) = − j 0 e n k T exp ( e U m n k T ) (5)
From a condition of parallelism of two straight lines, the angular factor of these lines should be identical:
j s c U o c = j 0 e n k T exp ( e U m n k T ) (6)
From equality (6) for effective value of SC voltage (Um) we will receive:
U m = n k T e ln ( j s c j 0 n k T e U o c ) (7)
Substituting the expression, defining effective value of SC voltage (Um), we receive for effective value of density of a current:
j m = j 0 ( exp ( e U m n k T ) − 1 ) − j s c (8)
j m = j s c ( n k T e U o c − 1 − j 0 j s c ) (9)
As it is known, both j0 saturation, and jsc short circuits, and Uoc―voltage of idling depend on temperature [
j 0 = j 00 exp ( − e φ k ( 1 T 0 − 1 T ) ) (10)
j s c = j 00 exp [ e φ k ( 1 T 0 − 1 T ) ] [ exp [ e φ n k T 0 ( U 0 o c φ − 1 + T 0 T ) ] − 1 ] (11)
U o c = ( U 0 o c − φ ) T T 0 + φ (12)
where U0oc―open circuit voltage at room temperature. As shown in work [
On the other hand, dependence of height of a potential barrier φ from temperature of SC at not so low temperatures can be described in a kind:
φ = φ 0 − γ T (13)
where φ 0 ―height of a potential barrier at temperature Т = 0, γ―temperature factor of height of the potential barrier, having identical sense with temperature factor of width of the band gap [
On
Now we pass to calculation of temperature dependence of effective value of SC current density. Delivering expressions for currents density of jo―saturation and Jshc―short circuit, and Uoc―voltage of idling in (9) is possible to receive the formula defining temperature dependence of effective value of density of SC current.
On
and γ = 5 × 10−5 V/К. It is visible that in the expressions received for temperature dependence of short circuit current density and of current effective value from temperature has distinction only in values of I - V not ideality factor (n) of SC. This says that electric current type in these points of I - V differs from each other. From drawing it is visible that, as well as the density, and a short circuit current, and effective value of current density of SC have a weak maximum at T = 200 K (Jm ≈ 119 mА). Value of this photovoltaic characteristic in temperatures more low T = 120 K (Section A) and above T = 470 K (Section C) begin will strongly decrease. Calculations also have shown that at T < 110 K and T > 540 K value of effective density of a current equals to zero (Jm = 0).
In the scientific point of view, influence of temperature on effective value of current density of a semiconductor SC is investigated. The new expression allowing more approximately explain of experimental dependence of SC photovoltaic characteristics from temperature is received. We will notice that the new formulas received in this work for definition of dependence of the basic photo-galvanic characteristics of solar cells from temperature can use for SC on any semiconductor material basis.
From the practical point of view, it is established that SC, made on semiconductor alloy AlGaAs-GaAs, is not expedient to use at temperatures lower T = 110 K and above T = 540 K (that follows because of equality to zero of effective value of current density of such SC).
The authors declare no conflicts of interest regarding the publication of this paper.
Rayimjon, A., Gulomjonovich, I.R. and Alisherovna, A.M. (2019) Temperature Stimulation of Effective Value of Density of the Current of Semiconductor Solar Cells. Energy and Power Engineering, 11, 92-97. https://doi.org/10.4236/epe.2019.112006