Perovskite solar cells are emerging photovoltaics that have attracted significant attention in industrial applications. Based on the superior attributes of the perovskite semiconductors, significant progress has been made. With planar and mesoporous architectures, high power conversion efficiency have been recorded in perovskite solar cells.
Electron selective layer is crucial to the photovoltaic performance of solar cells. High temperature treatment of the electron selective layer is imperative to achieve highly condensed and crystallized films for efficient perovskite solar cells. This extreme process increases the production cost and energy payback time. It also limits the application of perovskite solar cells in gadgets fabricated on plastic substrate. For this reason, it is indispensable to explore low-temperature substitutes.
A number of feasible approaches have been adopted to fabricate electron selective layers on plastic conductive substrates. Most of these methods implement planar configurations and do not employ mesoporous scaffold layer, which is normally synthesized at high temperature. Therefore, Dalian University of Technology researchers in China prepared amorphous niobium-modified tungsten oxide as an electron selective layer for flexible perovskite solar cells. The authors proved that WOx as a building block for electron selective layer could be fabricated at low temperature. Their work has been published in peer-reviewed journal, Nano Energy.
The authors prepared the electron selective layers from a mixture of tungsten ethoxide, ethanol and niobium ethoxide. The obtained precursor mixture was coated on the polyethylene naphthalate substrate and heated below 150 oC to achieve a smooth layer. They mixed 4-tert-butyl pyridine with lead chloride and N,N-dimethylformamide in a bid to optimize the crystallization process of perovskite layer. Silver was then evaporated on the samples’ surface to give the back contact.
The results from the x-ray diffraction spectroscopy indicated that the obtained electron selective layers were amorphous. Moreover, x-ray photoelectron spectroscopy results indicated that the predominant valence state of the layers was W6+ in addition to small amounts of W5+. The compound was therefore named WOX.
The authors prepared for the first time amorphous WOX though the solution approach. They found that this was a promising building block for low-temperature preparation of flexible perovskite solar cells. They developed an approach to modify optoelectronic behavior of electron selective layer using NbOx, which resulted in enhanced conductivity and donor density, suppressed charge combination and reduced surface traps states.
Using niobium-modified tungsten oxide as electron selective layer, high power conversion efficiencies up to 15.65% have been attained by flexible perovskite solar cells. The cells with electron selective layers prepared at room temperature also recorded a power conversion efficiency of 13.14%. The authors assessed the effect of the layer thickness on hysteresis characteristics of the cells. They suggested that a capacitance existed across the layer in the perovskite structure. The suggestion explained the effect of the layer thickness on the hysteresis attributes. The proposed approach will facilitate the development of novel and functional materials.
Kai Wang1, Yantao Shi1, Liguo Gao2, Rihan Chi1, Kun Shi1, Bingyi Guo1, Liang Zhao1, Tingli Ma2,3. W(Nb)Ox-based efficient flexible perovskite solar cells: From material optimization to working principle. Nano Energy, volume 31 (2017), pages 424–431.Show Affiliations
- State Key laboratory of Fine Chemicals, School of Chemistry, Dalian University of Technology, Dalian 116024, China
- School Petroleum and Chemical Engineering, Dalian University of Technology, Panjin Campus, Panjin 124221, China
- Graduate School of Life Science and Systems Engineering, Kyushu Institute of Technology, 2–4 Hibikino, Wakamatsu, Kitakyushu, Fukuoka 808-0196, Japan
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