engleski

Addressing boundary problems in solar cells by introducing ferroelectric modification to the nano-structured layer of charge transfer oxide material

Critical concern in multilayer solar cell (SC) is to enable overall compatibility of the active and passive layers. Modern 3rd generation SC aim at allowing high-efficiency transport of charge carriers between the photo-absorbing material and electrode. Here, charge transfer oxide layer (CTO) show great importance. In terms of CTO chemical composition, titania and zincite semiconductive materials stand out, yet the use of various nanostructural arrays (nanotubes, nanorods, etc.) may further contribute to overall efficiency upgrade. Namely, the substantial surface roughness that nano-arrays display can address the low lifetime of the carriers and transparency, efficiency and stability problems of SC’s. SC assembly starts with transparent electrode, thereon modified nanostructured semiconductive material, then photoactive, followed by hole transfer material and counter electrode. Combination of multistep wet-chemistry deposition, anodization, magnetron sputtering and electron-beam evaporation were employed. Non-contacted layers were characterized (and optimised) using structural (GIXRD, GISAX/GIWAXS), spectroscopy (Raman, absorbance and photoluminescence) and microscopy (FEGSEM/FIB), while contacted SC were checked for electric properties (IV, IS, QES), offering relevant information on electronic transport and recombination. (Micro)structural features of layers strongly correlate to energy levels during deposition and thus yield different susceptibility in preparing uniform layers at large scale. Origins of basically all bottlenecks were found at the layer boundary. Hence, we introduce an additional buffer core-shell layer in perovskite-type of structure between CTO and active layers. The ferroelectric properties of the buffer material allow specific electric environment and enable additional separation of the charge carriers. During buffer preparation CTO nanoarchitecture remained unaffected, subsequently to be infiltrated with small molecules, methylammoniumiodide perovskites and bulk-heterojunction polymers. Some materials fully infiltrate the nanoarchitecture and ensure charge transfer effect, while full infiltration of material with bigger building units still presents a challenge. Interfacial phenomena correlate to layers’ geometry and indicate complexity of distinguishing of the contributions. Preparations of such advanced interfaces significantly attribute to SC behaviour and act as milestone in their future upgrade.

solar cell

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