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(a) J-V characteristics under 100 mW/cm2 white light illumination for devices (QD Eg = 1.27 eV) annealed at various temperatures. (b) Device performance parameters Jsc (top), Voc (middle), and PCE (bottom) as a function of annealing temperature for two sets of devices from PbS QDs with bandgaps of 1.27 (white squares) and 1.65 eV (black squares).
(a) EQE spectra of devices where the QD films were annealed at various temperatures. (b) Voc dependence on the bandgap of the PbS QDs by either varying the size of the QDs from the synthesis or by thermal annealing one size of QDs in a film. For the black curve, the 1st exciton peak is derived from absorption spectra, while in the annealed films, the 1st exciton peak is monitored from the EQE shown in panel (a).
XRD of PbS QD thin films under various annealing temperatures. The inset is the calculated PbS domain size as a function of annealing temperature from the Scherrer equation.
(a) Room temperature DC conductivity for PbS QD films prepared on interdigitated Au electrode sets as a function of annealing at various temperatures. The dashed lines are guides to the eye for a linear relation (ohmic region) and power law of 2 (space charge limited) between the current and applied bias. (b) Arrhenius plot of thin PbS QD films under various annealing temperatures. The deep trap level (100 K–180 K) and shallow trap level (180 K–300 K) regions are separated by the dashed line, and the trap energy can be obtained by fitting the Arrhenius relation I ∼ exp(−Et /kT). The inset shows the activation energy of the Arrhenius fit as a function of temperature for both trap levels.
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