Rupendra Kumar Sharma

Zinc oxide (ZnO) is a low-cost, environmentally friendly material with unique optical properties and a wide variety of nano- and microstructures, making it attractive for applications in energy conversion, scintillators, photocatalytic wastewater treatment, electrochemical energy storage, and sensing. In this work, nominally undoped and Al-doped nanocrystalline ZnO (AZO) thin films were deposited by pulsed laser deposition (PLD) on commercial gold-based interdigitated electrodes (IDE) on glass substrates. Surface morphology and structure were characterized using Correlative Probe and Electron Microscopy (CPEM), combining Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM) to perform spatially correlated measurements. Longer deposition resulted in the growth of larger crystals and thicker ZnO layers, while Al doping only slightly affected grain size and reduced growth rate. Optical and optoelectronic properties were investigated by photothermal deflection (PDS) and photocurrent spectroscopy (PCS). The mobility edge was found to lie approximately 0.3 eV below the band gap. Space-charge-limited currents were observed at low voltages. Persistent photoconductivity indicates potential issues with charge transport.

In this work, we used calibrated numerical simulation models to optimize silicon heterojunction (SHJ) solar cells, with a focus principally on higher efficiency at lower illumination. The low‐light analysis is important because photovoltaic (PV) modules are exposed to varied illumination conditions depending on location, weather, and climate. Recently, we have established that for lower illumination, the SHJ configuration with thin and lower‐doped front p‐type emitter contact is a viable option for providing higher efficiency; however, that study was only performed for a low‐doped (~10 ¹⁵ cm ⁻³ ) c‐Si(n) absorber. In this work, we comprehensively optimized the SHJ configuration for a wide variation of absorber doping/resistivity (5 × 10 ¹⁴ –5 × 10 ¹⁷ cm ⁻³ /9.05–0.032 Ω cm) and observed that for highly doped (~5 × 10 ¹⁶ cm ⁻³ /0.141 Ω cm) absorbers, efficiency drops for thin and low‐doped p‐type emitters. On the contrary, a moderate to high doped (2 × 10 ¹⁶ –5 × 10 ¹⁶ cm ⁻³ /0.292–0.141 Ω cm) absorber with a standard p‐type emitter enhances efficiency most effectively under low light illumination, where the generated carrier density is low. Additionally, a combination of a moderate to high doped absorber, together with a doped a‐Si:H(p) contact layer for an optimized front electrode workfunction, further boosts efficiency irrespective of illumination. The other advantage of our optimization is the relaxed requirements of a higher work function (WF) of the front electrode necessary for a hole‐selective contact in SHJ solar cells. We achieved a remarkable 3.2% absolute increase at low illumination (0.01 suns), and a 1.4% absolute increase at 0.1 and 1.0 suns compared to an STC‐optimized cell (optimized experimentally for best efficiency at 1.0 sun). This analysis suggests designing PV modules providing energy production that is slightly better matched to the actual people’s energy needs throughout the day and year.

Nanorods of erbium-doped zinc oxide (ZnO:Er) were fabricated using a hydrothermal method. One batch was prepared with and another one without constant ultraviolet (UV) irradiation applied during the growth. The nanorods were free-standing (FS) as well as deposited onto a fused silica glass substrate (GS). The goal was to study the atomistic aspects influencing the charge transport of ZnO nanoparticles, especially considering the differences between the FS and GS samples. We focused on the excitons; the intrinsic defects, such as zinc interstitials, zinc vacancies, and related shallow donors; and the conduction electrons. UV irradiation was applied for the first time during the ZnO:Er nanorod growth. This led to almost total exciton and zinc vacancy luminescence reduction, and the number of shallow donors was strongly suppressed in the GS samples. The effect was much less pronounced in the FS rods. Moreover, the exciton emission remained unchanged there. At the same time, the Er³⁺ content was decreased in the FS particles grown under constant UV irradiation while Er³⁺ was not detected in the GS particles at all. These phenomena are explained.