Temperature-dependent current-voltage measurements are used to determine the dominant recombination path in thin-film heterojunction solar cells based on a variety of Cu(In,Ga)(Se,S)2 alloys. The activation energy of recombination follows the band gap energy of the respective Cu(In,Ga)(Se,S)2 alloy as long as the films are grown with a Cu-poor final composition. Thus, electronic loss in these devices is dominated by bulk recombination. In contrast, all devices based on absorber alloys with a Cu-rich composition prior to heterojunction formation are dominated by recombination at the heterointerface, with activation energies smaller than the band gap energy of the absorber material. These activation energies are independent from the S/Se ratio but increase with increasing Ga/In ratio.

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In this study, we have investigated the intersection behavior of the forward bias current-voltage (I-V) characteristics of the Al/TiO 2 /p-Si (MIS) structures in the temperature range of 100-300 K. The intersection behavior of the I-V curves appears as an abnormality when compared to the conventional behavior of ideal Schottky diodes and MIS structures. This behavior is attributed to the lack of free charge at a low temperature and in the temperature region, where there is no carrier freezing out, which is non-negligible at low temperatures, in particular. The values calculated from the temperature-dependent forward bias I-V data exhibit unusual behavior, where the zero-bias barrier height (φ b0 ) and the series resistance (R s ) increase with increasing temperature. Such temperature dependence of φ b0 and R s is in obvious disagreement with the reported negative temperature coefficient. An apparent increase in the ideality factor (n) and a decrease in the φ b0 at low temperatures can be attributed to the inhomogeneities of the barrier height, the thickness of the insulator layer and non-uniformity of the interfacial charges. The temperature dependence of the experimental I-V data of the Al/TiO 2 /p-Si (MIS) structures has revealed the existence of a double Gaussian distribution with mean barrier height values ( φb0 ) of 1.108 eV and 0.649 eV, and standard deviations (σ s ) of 0.137 V and 0.077 V, respectively. Furthermore, the temperature dependence of the energy distribution of interface state density (N ss ) profiles has been determined from forward bias I-V measurements by taking into account the bias dependence of the effective barrier height (φ e ) and n. The fact that the values of N ss increase with increasing temperature has been attributed to the molecular restructuring and reordering at the metal/semiconductor interface under the effect of temperature.

The current-voltage (I-V) characteristics of Al/TiO2/p-Si metal-insulator-semiconductor (MIS) structures have been investigated in the temperature range of 80–300 K. An abnormal decrease in the zero bias barrier height (BH) (ϕb0) and an increase in the ideality factor (n) with decreasing temperature have been explained on the basis of the thermionic emission (TE) theory with Gaussian distribution (GD) of the BHs due to the BH inhomogeneities. The temperature dependence of the experimental I-V data of the Al/TiO2/p-Si (MIS) structures has revealed the existence of a double GD with mean BH values (ϕ¯b0) of 1.089 and 0.622 eV and standard deviations σs of 0.137 and 0.075 V, respectively. Thus, the modified ln(I0/T2)−q2σ02/2(kT)2 versus q/kT plot gives ϕ¯b0 values and Richardson constants (A∗) as 1.108 and 0.634 eV and 31.42 and 23.83 A/cm2 K2, respectively, without using the temperature coefficient of the BH. The value of the effective Richardson constant of 31.42 A/cm2 K2 is very close to the theoretical value of 32 A/cm2 K2 for p-Si. As a result, the temperature dependence of the forward bias I-V characteristics of the Al/TiO2/p-Si (MIS) structure can be successfully explained on the basis of the TE mechanism with a double GD of the BHs.