engleski

Nanostructured zinc oxide as electron transport layer in perovskite solar cells

In perovskite solar cells (PSC), high photovoltaic performance is governed by the extent of electron mobility, achieved between the photoactive core layer and adjacent transport oxide layers. An effective PSC usually consists of an electron transport material (ETM) (such as mesoporous metal-oxide film) with adsorbed photoactive perovskite and a hole transport oxide deposited on top, all between electric contacts. Among these, TiO2 films have been widely used as ETM, especially nanostructured. However, the preparation of TiO2 films requires considerable thermal treatment, which limits the application at flexible substrates. Having similar electron band structure and physical properties to TiO2, ZnO, which can be easily solution-processed in a variety of nanostructured morphologies, is a viable low-temperature alternative for PSC with high power conversion efficiency (PCE). In this work, the role of the type and morphology of the ETM layer on the PSC performance was investigated, i.e. PSC devices were prepared using two different types of ETM layer configuration: a) zinc oxide ordered nanorod films, and b) titania mesoporous films. Devices were fabricated at indium tin oxide (ITO) glass substrates. The cells were prepared in protective atmosphere and characterized immediately upon fabrication. J/V measurements show the photovoltaic performance of the TiO2 devices surpasses that of ZnO nanorod PSC devices. Even though the nanorod morphology is tailored to increase their specific surface area and thereof the charge transfer, the solar cells fail to increase PCE on behalf of the high charge recombination in 1D ZnO nanostructure. The quantum efficiency (EQE) shows good utilization of the solar spectra, especially at lower wavelengths. Raman measurements show traces of PbI2 and PbBr2, but with high fluorescence and fast sample degradation hinder the feasibility of Raman characterization. X-ray diffraction (XRD) allows good insight in the presence of crystalline constituent and decomposition products. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) mapping allowed insight in homogenous incorporation and infiltration of perovskite layer on and into the ZnO nanorods. PSCs based on nanostructured ZnO show high margin for improvement on behalf of surface modifications of the ZnO layer like passivation or doping.

titanium oxide ; zinc oxide ; nano structured ; perovskite solar cells

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