Hsuan Ta Wu

Structural and photoelectron spectroscopic studies of band alignment at the Cu2ZnSnS4/CdS heterojunction with slight Ni doping in Cu2ZnSnS4

Knowledge of band-gap engineering and band-alignment matching at the Cu2ZnSnS4 (CZTS)/CdS interface are important for high-efficiency CZTS thin film solar cells. A negative conduction band offset (CBO) is usually obtained at the CZTS/CdS interface, forming a cliff interface and recombination center that reduces the photocurrent. We report a new attempt in which Ni was slightly doped into CZTS to change the band offset at the Cu2(Zn,Ni)SnS4 (CZNTS)/CdS interface (, ). Experimental results showed that the band gap of the CZNTS absorber was strongly associated with the Ni composition, changing from 1.43 eV in pure CZTS to a narrow band gap of 1.26 eV in CZNTS (). The valence band offset (VBO) values were −1.25 eV, − 1.20 eV, and −1.12 eV when x was 0, 0.1, and 0.3, respectively. The CBO at the interface varied from negative (−0.28 eV) to positive (0.02 eV) when x was changed from 0 to 0.3. This finding demonstrated that Ni doping is an efficient way to change the CBO from a cliff to a spike, thus is helpful in reducing the interfacial recombination and enhancing the photovoltaic properties.

Enhancing the electroluminescence efficiency of Si NC/SiO2 superlattice-based light-emitting diodes through hydrogen ion beam treatment

This paper presents a novel method for enhancing the electroluminescence (EL) efficiency of ten-period silicon-rich oxide (SRO)/SiO2 superlattice-based light-emitting diodes (LEDs). A hydrogen ion beam (HIB) was used to irradiate each SRO layer of the superlattices to increase the interfacial roughness on the nanoscale and the density of the Si nanocrystals (Si NCs). Fowler-Nordheim (F-N) tunneling was the major mechanism for injecting the carriers into the Si NCs. The barrier height of the F-N tunneling was lowered by forming a nano-roughened interface and the nonradiative Pb centers were passivated through the HIB treatment. Additionally, the reflectance of the LEDs was lowered because of the nano-roughened interface. These factors considerably increased the slope efficiency of EL and the maximum output power of the LEDs. The lighting efficiency increased by an order of magnitude, and the turn-on voltage decreased considerably. This study established an efficient approach for obtaining bright Si NC/SiO2 superlattice-based LEDs.