A solution-processed zinc oxide (ZnO) thin film as a buffer layer for polymer solar cells (PSCs) with an inverted device structure has been demonstrated. A power conversion efficiency (PCE) of 3.8% was observed from an inverted device structure with the ZnO buffer layer. Without the ZnO layer, PSCs only show a PCE of 1.67%, which is less than half the value observed from PSCs with the ZnO buffer layer. When operated at room temperature, no obvious degradation was observed from the PSCs with the ZnO layer after continuously illuminating the devices for 4 h. However, a significant degradation was observed from the PSCs without the ZnO buffer layer after illuminating the devices only for 1 h. Furthermore, PSCs with the ZnO buffer layer also show very good shelf stability; only 5% degradation was observed in PCEs after 47 days. All these results demonstrate that the ZnO buffer layer plays an important role in the enhancement of PSCs’ performance with an inverted device structure.

Oleic acid (OA) modified zinc-blende cadmium selenium nanocrystals (NCs) with different diameters, 3-5 nm, have been prepared. We find that the morphology and fluorescent properties of the samples are related to the preparation conditions such as the chain-length and concentration of the cadmium precursor as well as the concentration of OA. The hybrid solar cells based on the obtained spherical CdSe NCs as an acceptor and Poly(2-methoxy-5-(2'-ethylhexoxy)-p-phenylenevinylene) (MEH-PPV) as a donor show an energy conversion efficiency (ECE) as high as 0.85%, three times higher than that reported before for spherical CdSe NCs/conjugated polymer hybrid solar cells. When poly(3-hexylthiophene) (P3HT) is used as the donor phase instead of MEH-PPV, the energy conversion efficiency increases up to 1.08%. The solar cell based on CdSe NCs/conjugated polymer has the potential to open up new production technologies for hybrid solar cells based on semiconductor NCs.

Multiarmed CdS nanorods have been used as the electron acceptors to fabricate efficient hybrid solar cells. It was demonstrated that when pyridine was used as a solvent for spin coating an active layer consisting of MEH-PPV/CdS blend instead of chlorobenzene, short-circuit current of the device can typically be increased by six times. The FTIR transmission spectrum shows that pyridine replaces the surfactant (HDA) molecules attached to the nanocrystals' surface after posttreatment of CdS nanorods by refluxing in pyridine. Transmission electron microscopy, atomic force microscopy, current-voltage characteristics, photocurrent action spectra measurements, and photoluminescence quenching were used to characterize MEH-PPV/CdS blend spin-coated from pyridine solution. Thermal treatment of the blend films can further enhance the short-circuit current in the device. Best device performance was achieved with a power conversion efficiency of 1.17% under AM1.5 illumination (100 mW cm -2 ), significantly higher than that reported so far for MEH-PPV/CdS hybrid devices.

Here we demonstrate flexible polymer solar cells with a record high power conversion efficiency of 8.7% and a very high specific power of 400 W kg−1, by depositing a physical blend of a conjugated semiconducting polymer and a fullerene derivative on a highly flexible polyethylene terephthalate (PET) substrate.

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CdTe/CdSe nanocrystal (NC) solar cells with an inverted structure (ITO/ZnO/CdSe/CdTe/Au) have been successfully fabricated by a simple solution process coupled with layer-by-layer sintering techniques. It was found that the device performance is strongly dependent on the annealing strategy, the thickness of the acceptor layer and on the buffer layer of ZnO when the optimal thickness of CdTe is adopted. Without the ZnO buffer layer, a thin film of the CdSeNCs on an ITO substrate shows a rougher morphology, resulting in device shunting. However, when a 40 nm-thick ZnO buffer layer and 60 nm-thick CdSe were employed, the device shows a much higher PCE of 5.81% under device conditions, post-annealing at 340 8C. This value is the highest efficiency ever reported to date for a CdTe/CdSe NC solar cell. Comparing with CdTe/CdSe NC solar cells with the normal device configuration, this device with an inverted structure simultaneously offers good Ohmic contact for carrier collection and efficient harvesting of solar photons in a wide wavelength.

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