Electrical characterization of novel Si solar cells

A new approach for hybrid metal-insulator-semiconductor Si solar cells is adopted by the Institute of Fundamental Problems for High Technology, Ukrainian Academy of Sciences. In this technique, the porous silicon layers are created on both sides of single crystal wafers by chemical etching before an improved MIS cell preparation process. Using this technique, the solar cells with efficiencies above 15% have been obtained under AM1.5 condition (under 100 mW/cm2 illumination at 25 °C). In this work the dark current–voltage–temperature (I–V–T) characteristics of these cells are studied over a temperature range between 79 and 400 K. The dark capacitance–voltage (C–V) and conductance–voltage (G–V) behaviours of these cells at 100 kHz are analysed for the same temperature range. At room temperature C–V and G–V measurements are also made under illumination levels changing five folds. The diode ideality factors calculated from the dark I–V characteristics are significantly larger than unity and exhibit strong temperature dependence. The analysis of the temperature tendencies of diode ideality factor in these cells indicated that the current transport mechanism consists of both the trap-assisted tunnelling and the thermionic emission. While the temperature decreases, the barrier height calculations from I–V–T and C–V–T measurements showed that ϕB(I − V) decreases whereas ϕB(C − V) increases. The difference in ϕB(I − V) and ϕB(C − V) values and in their temperature dependence are explained by a model assuming Gaussian distribution of barrier heights. All the results are analysed after series resistance corrections.