In this paper, performance in hybrid solar cells based on ZnO nanorod array (ZnO-NA) is significantly improved by formation of a heterostructured ZnO/CdScore/shell nanorod array (ZnO-CdS-NA), the CdS shell effects on device performance including charge transport and recombination dynamics are discussed, and a model concerning ineffective polymer phase is proposed for understanding the charge generation upon CdS shell formation. The ZnO-CdS-NAs with varied CdS shell thickness (L) were prepared by depositing CdS quantum dots on the ZnO nanorods in the ZnO-NA. Solar cells were prepared by filling the interspaces between the nanorods in ZnO-NA or ZnO-CdS-NAs with poly(2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV). Compared to MEH-PPV/ZnO-NA devices, both open-circuit voltage (V oc ) and short-circuit current (J sc ) in MEH-PPV/ZnO-CdS-NA solar cells were dramatically improved depending on L,resulting in a peak efficiency of ca. 1.23% under AM 1.5 illumination (100 mW/cm 2 ) with a 7-fold increment for L = 6 nm. In particular, the experimental L-dependence of J sc agreed with the expectation from the proposed model and the V oc was improved from ca. 0.4 V for ZnO-NA up to around 0.8 V. Results demonstrate that in the MEH-PPV/ZnO-CdS-NA devices, the J sc correlates mainly with the charge generation subjected to the exciton generation altered by CdS shell formation, in which the polymer absorption is dominantly contributive; however, the V oc is determined by the energy difference between the highest occupied molecular orbital level of MEH-PPV and the conduction band edge of ZnO but significantly correlates with the quasi-Fermi levels of the electrons in ZnO nanorods.

This paper reports the chemical modification effects at charge separation interface on the performance of the hybrid solar cells consisting of poly(2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV) as an electron donor (D) and vertically aligned ZnO nanorod arrays as an electron acceptor (A). Results show that, with increasing the modification time T s for grafting dye Z907 onto the ZnO surface from 0 to 8 h, the charge transfer efficiency at the MEH-PPV/ZnO interface keeps increasing, the short circuit current (J sc ) increases and reaches a peak value at T s = 8 h, but the open circuit voltage (V oc ) increases within T s = 1-3 h and reduces with further increasing T s up to g6 h. By controlling the T s , a peak power conversion efficiency of η = 0.61% at AM 1.5 illumination (100 mW/cm 2 ) is obtained for T s = 6 h. It is revealed that the Z907 modification mainly contributes to the enhanced J sc by increasing the charge separation efficiency as a result of the improved electronic coupling property at the D/A interface rather than the light harvesting; on the other hand, the Z907 modification reduces (T s = 1-3 h) or increases (T s g 6 h) the surface defect concentration of the ZnO nanorods, resulting in the increased or reduced V oc (or electron lifetime τ e ). It is demonstrated that trapping electrons by the surface defects may facilitate the charge separation at the D/A interface in the MEH-PPV/ZnO devices, and both V oc and τ e correlate to the occupation of injected electrons in conduction band and surface defects. Further analysis provides the relation between V oc and τ e in those devices.

The under-coordinated defects within perovskite and its relevant interfaces always attract and trap the free carriers via the electrostatic force, significantly limiting the charge extraction efficiency and the intrinsic stability of perovskite solar cells (PSCs). Herein, self-diffusion interfacial doping by using ionic potassium L-aspartate (PL-A) is first reported to restrain the carrier trap induced recombination via the reconstruction of energy level structure at SnO 2 /perovskite interface in conventional n-i-p structured PSCs. Experiments and theories are consistent with the PL-A anions that can remain at the SnO 2 surface due to strong chemical adsorption. During the spin-coating of the perovskite film, the cations gradually diffuse into perovskite and endow an n-doping effect, which provides higher force and a better energy level alignment for the carrier transport. As a result, they obtained 23.74% power conversion efficiency for the PL-A modified small-area devices, with dramatically improved open-circuit voltage of 1.19 V. The corresponding large-area devices (1.05 cm 2 ) achieved an efficiency of 22.23%. Furthermore, the modified devices exhibited negligible hysteresis and enhanced ambient air stability exceeding 1500 h.