Performance Improvement in Polymer/ZnO Nanoarray Hybrid Solar Cells by Formation of ZnO/CdS-Core/Shell Heterostructures

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• 作者：Qi Cui ; Changwen Liu ; Fan Wu ; Wenjin Yue ; Zeliang Qiu ; Hui Zhang ; Feng Gao ; Wei Shen ; Mingtai Wang
• 刊名：The Journal of Physical Chemistry C
• 出版年：2013
• 出版时间：March 21, 2013
• 年：2013
• 卷：117
• 期：11
• 页码：5626-5637
• 全文大小：497K
• 年卷期：v.117,no.11(March 21, 2013)
• ISSN：1932-7455

文摘

In this paper, performance in hybrid solar cells based on ZnO nanorod array (ZnO-NA) is significantly improved by formation of a heterostructured ZnO/CdS-core/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/cm²) 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.