(Color online) Schematic illustration of the effective bandgap model. The scheme shows the HOMO and LUMO levels of the electron donor and acceptor. The effective bandgap is the energy difference between the acceptor’s LUMO and the donor’s HOMO level. The energy of charge transfer complexes is close to the effective bandgap and determines the upper limit of the open-circuit voltage ( ).
Absorption spectra for all used CdSe nanoparticle samples dissolved in pyridine. The four solutions with smaller nanoparticles exhibit strong and well-pronounced absorption peaks, and the intensity is normalized to the maximum of the first excitonic peak. The absorption spectrum of the largest particles (not normalized) is overlaid with a scattering curve (see text for details), but a weakly pronounced peak can be recognized at ∼ 680-700 nm.
Typical TEM image of quasi-spherical CdSe nanocrystals stabilized by oleic acid.
(Color online) Part (a) shows a schematic representation of the solar cell geometry. Part (b) shows representative I-V curves of selected solar cells with different sizes of the CdSe nanoparticles in the dark as well as under irradiation with simulated sunlight (100 mW/cm2 AM 1.5 g conditions).
(Color online) Open-circuit voltage under irradiation with simulated sunlight (100 mW/cm2, AM 1.5 g conditions) in dependence of the bandgap of the CdSe nanocrystals. The bandgap has been calculated from the absorption spectra in Fig. 2.
Short-circuit current density, fill factor, and power conversion efficiency in dependence of the diameter of the CdSe nanoparticles.
(Color online) Representative EQE spectra of selected hybrid solar cells with differently sized CdSe nanocrystals and P3HT.
(Color online) Open-circuit voltage and short-circuit current density as a function of temperature for a P3HT/CdSe solar cell with CdSe nanocrystals of d = 4.0 nm size. The illumination intensity was 100 mW/cm2.
(Color online) The short-circuit current density of the same sample as in Fig. 8 as a function of illumination power at different temperatures.
Photocurrent density Jphot derived from the EQE measurements compared to the short-circuit current density Jsc obtained from the I-V curves. The standard deviation σ is given in the same units as the current.
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