Here we employ transient optoelectronic techniques to study the charge
present in the device and the nongeminate recombination rate in hybrid PbS/C60 planar
heterojunction solar cells under working conditions. We find that in low light intensity
conditions there are very few charges present in the solar cell and that the charge
increases linearly with voltage, suggesting that most of the charge resides at the
electrodes (capacitive charges). At higher applied light bias, the charges stored in the
device increase exponentially. The carrier lifetime is very short (τ < 1 us at 1 sun; 1 sun =
100 mW/cm2 of sun-simulated light) when compared to organic solar cells. By
correlating the charge carrier lifetime with the device charge density, we successfully
reconstruct the photocurrent− voltage (J−V) curve at 1 sun, demonstrating that fast
nongeminate recombination losses limit the efficiency in these quantum dot-based
devices.
