Analysis of transient photocurrents in Cu(In,Ga)Se2 thin film solar cells

Abstract

A transient photocurrent measurement with a zero-field time-of-flight configuration was carried out on ITO/ZnO/CdS($n$ -type)/${\mathrm{Cu(In,Ga)Se}}_{\mathrm{2}}\mathrm{(p}$ -type, $\text{Eg=1.15\hspace{0.17em}}\mathrm{eV}$ )/Mo/glass solar cell to get the information about the minority carrier transport on the ${\mathrm{Cu(In,Ga)Se}}_{\mathrm{2}}$ film. The transient photocurrent was recorded after the incidence of a subnanosecond pulse light (500 nm wavelength) from the back side through the Mo thin film (<0.5 μm). The analysis of the transient photocurrent was conducted by using the time-dependent diffusion current equation. Consequently, the values of $\text{1.0\hspace{0.17em}}{\mathrm{cm}}^{\mathrm{2}}\mathrm{/s},$ 100 ns, and ${10}^3\hspace{0.17em}\mathrm{cm/s}$ as the diffusion coefficient, the minority carrier lifetime, and the recombination velocity in the ${\mathrm{Cu(In,Ga)Se}}_{\mathrm{2}}\mathrm{/Mo}$ interface, respectively, were obtained on the ${\mathrm{Cu(In,Ga)Se}}_{\mathrm{2}}$ film. These data corresponded to the electron beam induced current line profile data, and the experimental data of $J_0,$ analyzed by current–voltage characteristics.