Interface structure of PN junctions in NiO–WO3–FTO photoelectrode for efficient DSSCs and enhanced photoresponses

• Photoelectrode containing PN junctions was synthesized by a simple method. • Photoelectrode achieved 91.5% full-spectrum absorption of sunlight. • Photoresponses mechanism of PN junctions was revealed regarding energy level structure, depletion region, and space charge. • Potential application of NiO-WO 3 -FTO photoelectrode in DSSCs was elucidated. In the current global energy crisis, dye-sensitized solar cells (DSSCs) with excellent performance and loaded with P/N type semiconductor heterojunctions (PN junctions) has attracted huge attention in renewable energy research. This study reports the unique energy level structure and synergistic effect of the PN junction interfaces in response to light. Photoelectrodes containing NiO–WO 3 nano-powder (NPs) layers were synthesized on fluorine-doped tin oxide (FTO) substrates by a simple method, which can respond to full-spectrum absorption of sunlight. In this study, the carrier densities in the P-type and N-type semiconductor heterojunctions at a light intensity of 2 SUN (2000 W/m 2 ) were 1.38 × 10 28 m −3 and 4.27 × 10 28 m −3 , respectively. These values are 2.7 and 1.9 times higher than those in dark conditions, indicating that the electrode excels in converting light into electrical energy, outperforming other reported results. Although PN junctions are often used in applications such as DSSCs and energy storage devices, the photoresponses of the heterojunction energy band structure still need to be elucidated. In this work, the analysis of the charge depletion region width revealed the electron transfer mechanism during the charge and discharge process under light illumination. Additionally, the electrochemical experiment demonstrated the impact of space charge at the interface on the energy levels. Furthermore, by studying the energy level structure of the PN junction, it was confirmed that the internal resistance decreases and the photocurrent increases under light conditions. The design and application flexibility of the PN junctions were verified based on these results and the possible applications of this photoelectrode in solar cells were elucidated.