Processing of nanocrystalline thin films of selenium and formation of FTO/p-Se/n-CdS/In heterojunctions for photovoltaic response

Abstract

Thin films of nanocrystalline selenium (Se) of different thicknesses were grown on annealing from 323 to 398 K. The crystallinity of the layers increased with annealing temperatures (TA). The temperature thickness correlations were established. The layers exhibited spherical-shaped particles at higher annealing temperatures. The grown layers possess hexagonal crystal system with space group P3121(152); it shows prominent planes along the a-axis. The bandgap (Eg) decreases from 2.18 to 1.94 eV, 2.12 to 1.82 eV, and 2.13 to 1.84 eV with changes in TA of 700, 270, and 150 nm thick layers, respectively. The high absorption coefficient (α) values ∼ 1 × 105 cm−1 observed in all films makes it suitable as an absorber layer in a solar cell structure and an optical sensor. The FTO/p-Se/n-CdS/In heterojunction diodes provide zero-bias barrier height (фbo) of 0.788(7) eV. The open circuit voltage (Voc) of FTO/p-Se (150 nm)/n-CdS(200 nm)/In a photovoltaic cell was observed to be 55 mV.

Keywords

• Nanocrystalline selenium layers
• Bandgap tuning
• Heterojunction diode
• Photovoltaic cell