Browsing by Author "Birabwa, Denise Joanitah"

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    Biosynthesized nickel oxide honeycomb nanostructures for DSSC counter electrode: a joint experimental and density functional theory study
    (Materials Research Express, 2026-01-05) Nasejje, Stella; Mushebo, Emmanuel; Birabwa, Denise Joanitah; Diale, Mmantsae; Mukhokos, Emma Panzi
    The urgent need to address fossil fuel challenges has led to a surge in green energy technologies, including solar cells. Nanodimensional particles, particularly 2D nanostructures, have shown great potential in these technologies due to their high surface area-to-volume ratio. Nickel oxide (NiO) is a promising p-type semiconductor for solar cell photo-cathodes, offering remarkable physical and chemical properties at a relatively low cost. However, its surface morphology, area, and pores have a significant impact on performance.Traditional chemical synthesis methods for NiO nanostructures have several drawbacks, including the use of hazardous precursors.To address this, we present for the first time a novel bioengineering method using bamboo shoot extract to produce 2D NiO nanostructures. The results have been supported by Density Functional Theory (DFT) calculations. The DFTcalculations revealed that NiO is a p-type semiconductor with direct band gap for spin-down at Г.The results show that the bioengineered NiO nanostructures exhibit high crystallinity and a honeycomb-like morphology.We successfully integrated these nanoparticles into a dye-sensitized solar cell (DSSC), demonstrating their viability as a counter electrode.The cell exhibits promising performance,with a short-circuit current density of 0.113 mA cm−2 and an efficiency of 0.0057%.This study presents a straight forward, cost-effective, and environmentally friendly method for bioengineering NiO honeycomb-like nanostructures,thereby paving the way for sustainable energy solutions.
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    Grouped discrete Hartley transform precoding for low-complexity PAPR reduction in ACO-OFDM visible light communication systems
    (Journal of Optical Communications, 2026-09-07) Niwareeba, Roland; Birabwa, Denise Joanitah; Ssemakula, John Bosco
    The high peak-to-average power ratio (PAPR) remains one of the major challenges affecting asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM) systems used in visible light communication (VLC). Although transform precoding techniques such as discrete Hartley transform (DHT) precoding can effectively reduce PAPR, their computational complexity increases significantly as the number of subcarriers increases, limiting practical implementation in large-scale systems. In this paper, a grouped discrete Hartley transform (G-DHT) precoding scheme is proposed for low-complexity PAPR reduction in ACO-OFDM systems. The proposed technique partitions the input symbol vector into smaller groups and independently applies DHT precoding within each group before OFDM modulation. This significantly reduces computational complexity while preserving the PAPR reduction capability of conventional DHT precoding. Simulation results show that the proposed scheme achieves measurable PAPR reduction without noticeable bit error rate (BER) degradation. At a complementary cumulative distribution function (CCDF) of 10−3, the proposed G-DHT scheme with group size G = 128 achieves approximately 0.95 dB PAPR reduction relative to conventional ACO-OFDM while reducing computational complexity by about 50 % compared with full DHT precoding. The results indicate that grouped DHT precoding provides an effective trade-off between PAPR reduction performance and implementation complexity in optical OFDM systems.