Impact of Band-Gap Graded Intrinsic Layer on Single-Junction Band-Gap Tailored Solar Cells

Objective: The work investigates the performance of intrinsic layers with and without band-gap tailoring in single-junction amorphous silicon-based photovoltaic cells. The work proposes single-junction amorphous silicon solar cells in which band-gap grading has been done between layers as well as within each layer for the first time. Materials & Methods: The samples of hydrogenated amorphous silicon-germanium with different mole fractions are fabricated, and their band-gaps are validated through optical characterization and material characterization. A single-junction solar cell with an intrinsic layer made up of hydrogenated amorphous silicon (aSi:H) having a band-gap of 1.6 eV is replaced by continuously graded hydrogenated amorphous silicon-germanium (aSi1-xGe x :H ) intrinsic bottom layers having band-gaps ranging from 0.9 eV to 1.5 eV. The proposed structure has been considered as a variant of previously designed single-junction band-gap tailored structures. Results: The suitable utilization of band-gap tailoring on the intrinsic absorber layer aids more incident photons in energy conversion and thereby attain a better short circuit current density of 19.89 mA/cm2. Conclusion: A comparative study on performance parameters of solar cell structures with graded band-gap intrinsic layer and the ungraded single band-gap intrinsic layer has been done. The graded band-gap intrinsic layer structure results in better conversion efficiency of 15.55%, while its ungraded counterpart contributes only 14.76 %. Further, the proposed solar structure is compared with the performance parameters of recent related works. The layers used in the proposed solar structure are of amorphous-phase only, which reduces structural complexity. The use of a lesser number of active layers reduces the number of fabrication steps and manufacturing cost compared to state-of-the-art.

Band Gap Tailoring, Size Modulation and Photoluminescence Properties of Mn/Cu doped ZnS Nanostructures

ZnS, Mn added ZnS (Zn0.97Mn0.03S) and Mn, Cu dual doped ZnS (Zn0.95Mn0.03Cu0.02S) QDs have been prepared using co-precipitation technique. The influence of Mn and Cu addition on the morphology, structure and photoluminescence properties of Mn/Cu incorporated ZnS have been examined. Cubic structure of the synthesized samples was confirmed by X-ray diffraction patterns. The incorporation of Cu in Zn-Mn-S lattice not only decreased the particle/grain size and also generates more defect based luminescent activation centres. The reduced energy gap by Mn addition was explained by sp-d exchange interaction and the elevated energy gap in Cu, Mn dual doped ZnS was expalined by Burstein–Moss effect. The tuning phenomenon of size as well as the energy gap in ZnS by Mn/Cu addition promote these materials for nano-electronic applications. FTIR spectra confirmed the presence of Mn/Cr-Zn-S bondings. The substitution of Mn /Cu provides an effective control over tuning of different emission colours which signifies their applications like light emitting diodes.