\documentclass{scrartcl}
\usepackage{color}
\usepackage{multicol}
\usepackage[final]{graphicx}
\usepackage{pst-plot,pstricks}
\begin{document}
	\psset{xunit=2cm,yunit=2cm}
	\begin{pspicture}(-0.5,-0.5)(5,1.5)
		\psaxes[Dx=5,Dy=5]{->}(0,0)(-0.5,-0.5)(5,1.5)
		\psline[linecolor=green,linestyle=dashed](-0.5,0)(0,0)
		\psline[linecolor=green,linestyle=dashed](0,0)(0,1)
		\psline[linecolor=green,linestyle=dashed](0,1)(5,1)
		\psplot[plotstyle=curve]{0}{5}{2.71828 x -1 mul exp}
		\psplot[plotstyle=curve,linestyle=dashed]{0}{1}{x -1 mul 1 add}
		\rput[l](4.7,0.2){$t$}
		\rput[r](0,1.5){$U\left(t\right)$}
		\rput[r](0,1){$U_0$}
		\rput(1,-0.2){$t_0=RC$}
	\end{pspicture}
\end{document}
