Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
1550394 | Solar Energy | 2013 | 11 Pages |
Nanostructured ZnO/In2S3/CuInS2 superstrate solar cell with all component layers deposited by a low cost chemical spray pyrolysis (CSP) method is characterized. The characteristics of a cell based on a nano-columnar ZnO window layer and a thin film reference prepared by spray are compared. The aim is to determine the dominating non-ideality and the recombination mechanism of these cells in both dark and illuminated conditions and relate the findings to the imperfections in the cell materials. We performed J–V–T (current–voltage–temperature) measurements in dark and under 0.5–100 mW/cm2 illumination intensities, and admittance spectroscopy, in the temperature range of 100–360 K. We further measured EQE (external quantum efficiency) at room temperature. The solar cell outputs at AM1.5 of the flat reference cell are: Voc = 497 mV, Jsc = 6.4 mA/cm2, FF = 62%, η = 2%. The use of a nanostructured instead of a flat window layer resulted in short-circuit current density Jsc = 12.2 mA/cm2 and efficiency of η = 3% at the expense of slightly reduced open-circuit voltage Voc = 430 mV and fill factor FF = 58%. Interestingly, the nanostructured cell performs worse than the flat reference at low illumination intensity, as also indicated by illumination dependent shunt conductance. The diode ideality factor of both cells has a significant temperature and illumination dependence. The absorber bandgaps deduced from EQE are 1.5 eV for the flat cell and 1.3 eV for the structured cell. The nanostructured cell shows an increase of light scattering ability accompanied by a less effective charge carrier separation, compared to those of the flat reference cell. The extrapolation of Voc(T) to 0 K yields 740–830 meV and 950–990 meV at varied illumination intensity, for the structured and the flat reference cell respectively, pointing to a non-midgap defect recombination. C–f–T (capacitance – ac frequency – temperature) analysis indicates that the structured cell has a higher concentration of defects and an additional band of defects. This further explains the limited performance enhancement of the structured cell over the flat cell. The illumination dependent cell parameters reveal that copper diffusion from absorber to buffer layer is likely. To eliminate problems associated with Cu diffusion, binary compounds like Sb2S3 or SnS for use as absorber material are considered to further develop the low-cost superstrate type solar cell deposited by the CSP method.
► We characterize ZnOrod/In2S3/CuInS2 superstrate solar cell and a ‘flat’ reference cell. ► Compared to the reference cell, an increase of efficiency is reported at A.M1.5. ► Decreased performance at low light intensity is explained with In2S3 photosensitivity. ► Ideality factors depend strongly on cell temperature and illumination intensity. ► Interface recombination and high series resistance limit the cell output.