Towards Green Energy and Power Integration in Africa

• Robinson Juma Musembi (University of Nairobi, Kenya)

Many countries in Africa have different energy mixes as energy sources, but in most cases these sources are usually insufficient and are often supplemented by stand-alone systems instead of relying on utilities. Different countries have different comparative advantages when it comes to power generation, there are those generating from hydroelectricity, thermal power generation, geothermal, wind turbine sources, solar, etc. furthermore, different countries can generate more energy than they can deliver for consumption in the form of grid connections, this has led to countries trying to export the excess energy to their neighbouring countries. In order to maximize the benefits of exporting energy, many countries have entered into bilateral agreements to export electricity, resulting in so-called electricity pools. There are five power pools in Africa that are at an advanced stage of power integration.

The role of hydrogen in reducing the greenhouse gas emissions

• Mmantsae Diale (University of Pretoria, South Africa)

Hydrogen has been used over decades as an important gas in many aspects of science. It was derived generally from grey methods, which increases the carbon footprint. The new way of appreciating the role of hydrogen in reducing greenhouse emissions is found in transitioning from grey to green hydrogen. This lecture aims to share different methods of producing clean hydrogen for sustainable environment. The most significant method to be shared is the production of hydrogen from water splitting, focusing the lecture on the need to embrace the natural systems to produce and store electricity. Hydrogen production in artificial photosynthesis is mimicked from natural photosynthesis, where energy is produced from sunlight, carbon dioxide and water, with water vapour as the only by-product of the reaction. In addition, the lecture will also teach participants the importance of embracing multi-disciplinary approached to grow in scientific research.

Nano-Activities in Solar & GREEN Hydrogen within the UNESCO Africa NanoChair

• Malik Maaza (iThemba LABS)

OXIDE PEROVSKITES NANOPARTICLES THIN FILMS FOR HIGH LIGHT ABSORPTION AND WHITE LIGHTSOURCE

• Diouma Kobor (University Assane Seck of Ziguinchor (UASZ))

1) Aim and approach Inorganic thin film PV is mainly based on CdTe, amorphous Si or CIGS. Very recently, hybrid perovskites emerged with a maximum yield of 23 %. However, these materials have problems of stability, reliability, toxicity and scale (cell size). Of course, research in this area is focused on solving these challenges, but success is not guaranteed. An alternative route, inorganic oxides, could have significant advantages. The ideal bandgap for an active photovoltaic layer for the solar spectrum is about 1.3 eV. However, oxides with such values are rare. One of the most studied oxides to date as a photovoltaic active layer is cuprous oxide Cu2O. Its bandgap width is around 2.1 eV and is therefore not ideal for the solar spectrum. Conversion efficiencies generally do not exceed 4%. In this project we propose to study a type of emerging solar cell that is based on ferroelectricity. In this type of solar cell, a junction p-n is not necessarily necessary, the opposite conventional solar cells. Interesting conversion efficiencies are starting to be achieved with this type of cell (up to 8.1% in 2015), however the mechanisms are still not well understood and several challenges at the material and engineering levels need to be addressed. Our aim is to fabricate a novel type of ferroelectric oxides perovskites as thin film form using nanoparticles on silicon and conductive glass (ITO) substrates to improve the light absorption and optical application. 2) Scientific innovation and relevance Ferroelectrics have recently attracted attention as a candidate class of materials for use in photovoltaic devices, and for the coupling of light absorption with other functional properties [1–3]. In these materials, the strong inversion symmetry breaking that is due to spontaneous electric polarization promotes the desirable separation of photo-excited carriers and allows voltages higher than the bandgap, which may enable efficiencies beyond the maximum possible in a conventional p–n junction solar cell [4–5]. Ferroelectric oxides are also stable in a wide range of mechanical, chemical and thermal conditions and can be fabricated using low-cost methods such as sol–gel thin-film deposition and sputtering [3]. The objective of this paper is to initiate an innovative photovoltaic technology based on novel inorganic and multifunctional oxide materials with suitable bandgap widths. These oxides are more stable, need less perovskites and facile to be integrate in silicon technology. We aim to synthesize ferroelectric materials that absorb a large part of the solar spectrum with reduced bandgap widths and give high Voc value. Our interest was in Pb(Zn1/3Nb2/3)O3-PbTiO3 (PZN-PT) perovskites that revealed excellent ferroelectric, piezoelectric and ferroelastic properties in solid state [7]. However, despite these excellent properties and perspectives to use them in solar cells devices, the veritable challenge is to fabricate them as in thin films form because of their incongruent melting point. To overcome this challenge, oxide perovskites nanoparticles were dispersed in an inorganic gel (for Si substrate) and biopolymer (for ITO substrate). They were deposited by spin coating on nanostructured silicon and ITO substrates. Optical characteristics in UV-Visible and Near IR ranges, photoluminescence and Raman Luminescence were performed. 3) Results/conclusions/perspectives The addition of the HTM layer strongly increases the absorption throughout the visible spectrum and IR region as shown in Figure 1. HTM increases the absorption value in the whole visible region (around 100%) and decreases slightly to between 85 and 95 % in IR region. The Mn doping reduces slightly the absorption value in Near IR region while no change is observed in visible one. The results show good perspectives for solar cells application. The biopolymer1 seems to have less influence on the absorption compared with HTM. The same behavior was found for the Silicon nanowires samples with perovskites dispersed on their surfaces. According to the SEM images we obtained thicknesses of 1.600 μm, 1.505 μm and 1.765 μm respectively for ITO, TiO2 and np-PZN-PT-biopolymer1/HTM layers. This allowed us to confirm the value of the thickness of the ITO given by the supplier (1.6 μm). The I-V characterization shows that lightning could improve polarization between 120 to 300 % showing good perspectives for photoferroelectric application. The Voc value is very high (2.1 eV) compared to the silicon one (0.6 eV) for a sample composed to ITO/TiO2/np-PZN-4.5PT(perovskite)/biopolymer2/HTM/Ag (Figure 2). The IV curve signs depend to the polarization orientation. Other investigations are in progress especially on the stability in time and temperature. REFERENCES: [1] Choi, T., Lee, S., Choi, Y., Kiryukhin, V. & Cheong, S.-W., Switchable ferroelectric diode and photovoltaic effect in BiFeO3., Science 324, 63–66 (2009). [2] Yang, S. Y. et al., Above-bandgap voltages from ferroelectric photovoltaic devices. Nature Nanotechnol. 5, 143–147 (2010). [3] Cao, D. et al., High-efficiency ferroelectric-film solar cells with an n-type Cu2O cathode buffer layer. Nano Lett. 12, 2803–2809 (2012). [4] Fridkin, V. M., Photoferroelectrics (Springer, 1979). [5] Inoue, Y., Sato, K., Sato, K. & Miyama, H., Photoassisted water decomposition by ferroelectric lead zirconate titanate ceramics with anomalous photovoltaic effects, J. Phys. Chem. 90, 2809–2810 (1986). [6] Young, S. M. & Rappe, A. M. First principles calculation of the shift current photovoltaic effect in ferroelectrics. Phys. Rev. Lett. 109, 116601 (2012). [7] Kobor, D., Synthesis and characterization of PZN-4.5PT single crystals by flux method, phD thesis, INSA Lyon, France, 2005.

Materials Design Principles for Organic Solar Cells: Case Study on Anthracene-Based Poly(Arylene-ethynylene)-alt-poly(arylene-vinylene)s

• Daniel Ayuk Mbi Egbe (African Network for Solar Energy, Jena, Germany)

Daniel Ayuk Mbi Egbe 1. African Network for Solar Energy, Schillerstr. 5, 07745 Jena, Germany 2. Institute of Polymeric Materials and Testing, Johannes Kepler University Linz, Linz, Austria 3. Department of Chemistry, Material Science, Innovation and Modelling Research Focus Area, North-West University, Mafikeng. Private Bag X2046, Mmabatho 2745, South Africa. 4. College of Science and Technology, University of Rwanda, KN 7 Ave, P.O. Box 3900, Kigali, Rwanda. Emails: daniel.egbe@ansole.org /daniel_ayuk_mbi.egbe@jku.at Since the discovery of electrical conductivity in doped polyacetylene by Shirakawa et al. [1], enormous progress has been achieved in the design, synthesis and detailed studies of the properties and applications of -conjugated polymers. The first part of this lecture will focus on the various chemical synthetic approaches which have led to efficient materials for organic solar cells, such as lowering the material energy band gap, or broadening the material absorption spectra, or adjusting the donor material HOMO and LUMO energy levels to those of the widely used acceptor materials PC60BM and PC70BM, or designing of compatible non-fullerene acceptor (NFA) materials, etc.[2]. In the second part of the lecture, the focus will be directed on anthracene-based poly(arylene-ethynylene)-alt-poly(arylene-vinylene)s, PAE-PAVs, a new class of conjugated materials combining the interesting intrinsic properties of both poly(arylene-ethynylene)s (PAEs) and poly(arylene-vinylene)s (PAVs) in addition to structure-specific features [3]. With these materials, we were able to demonstrate that by systematic variation of the nature (linear and/or branched), number and position of the laterally grafted alkoxy side chains and by fine tuning of the molecular-weight parameters, efficient photoactive polymers have been synthesized, which have exhibited state-of-the-art solar cells efficiencies of PPV-based materials and have served as basis in the gaining of valuable insights on the nanomorphology of solar cells active layers [4]. Keywords: Conjugated polymers, synthesis, band gap tuning, organic solar cells References 1. H. Shirakawa et al. Chem. Soc. Chem. Commun. 1977, 578. 2. a) Y.-J. Cheng et al. Chem. Rev. 2009, 109, 5868. b) H. Zhou et al. Macromolecules 2012, 45, 607-, c) C. L. Chochos et al. Prog. Polym Sci. 2011, 36, 1326. d) Z. Zheng, et al, Adv. Mater. 2017, 29, 1604241 3. a) D. A. M. Egbe et al. Prog. Polym. Sci. 2009, 34, 1023. b) D. A. M. Egbe et al. J. Mater. Chem. 2011, 21, 1338 c) N. Bouguerra et al. Macromolecules 2016, 49, 455. d) C. Ulbricht et al. Polym. Chem. 2019, 10, 5339 4. a) P. A. Troshin, et al. Adv. Energy Mater. 2013, 3, 161. b) C. Kästner et al. J. Mater. Chem. A 2013, 1, 3961.c) F. Tinti et al. RSC Adv. 2013, 3, 6972. d) Kästner, C. et al., J. Mater. Chem. A 2015, 3, 395