Charge transport and recombination in bulk heterojunction solar cells studied by the photoinduced charge extraction in linearly increasing voltage technique

Charge carrier mobility and recombination in a bulk heterojunction solar cell based on the mixture of poly[2-methoxy-5-(3,7-dimethyloctyloxy)-phenylene vinylene] (MDMO-PPV) and 1-(3-methoxycarbonyl)propyl-1-phenyl-(6,6)-${\mathrm{C}}_{61}$ (PCBM) has been studied using the novel technique of photoinduced charge carrier extraction in a linearly increasing voltage (Photo-CELIV). In this technique, charge carriers are photogenerated by a short laser flash, and extracted under a reverse bias voltage ramp after an adjustable delay time $\left(t_{\mathrm{del}}\right)$ . The Photo-CELIV mobility at room temperature is found to be $\mu =2\times {10}^{-4}{\mathrm{cm}}^2{\mathrm{V}}^{-1}{\mathrm{s}}^{-1}$ , which is almost independent on charge carrier density, but slightly dependent on $t_{\mathrm{del}}$ . Furthermore, determination of charge carrier lifetime and demonstration of an electric field dependent mobility is presented.