Power-conversion-efficiency Enhancement of Silicon Solar Cell Implemented with Energy-down-shifting using Core/Shell Quantum Dots

Abstract

Photovoltaic (PV) cells have recently attracted attention as a renewable, sustainable source of electricity, because they are a clean energy source, have a low fabrication cost, and can be processed on a flexible substrate. Therefore, in this study, we investigated the power conversion efficiency (PCE) enhancement for silicon solar cell implemented with energy-down-shifting (EDS) via core/shell quantum dots (QDs). First, we implemented the EDS layer using CdSe/ZnS core/shell QDs on p-type silicon solar-cells to absorb more UV light. CdSe/ZnS core/shell QDs demonstrated clear evidence of EDS, which absorbed UV lights and emitted green-light photo-luminescence (PL) signals with 542 nm wavelengths. The implementation of 0.2 wt% (8.8 nm of QDs layer) green-light emitting CdSe/ZnS core/shell QDs reduced the surface reflectance of the textured surface with SiNX film on silicon solar-cell from 27 to 15% and enhanced the external-quantum-efficiency (EQE) of silicon solar-cells around 30% in the ultra-violet (UV) wavelength region, thereby enhancing PCE for p-type silicon solar-cells by 5.5%p. Second, we found that Cd0.5Zn0.5S/ZnS core (4.2 nm in diameter)/shell (1.2 nm in thickness) QDs demonstrated a typical EDS (2.76~4.96 → 2.81 eV), which absorb UV light (250~450 nm in wavelength) and emit blue visual light (~442 nm in wavelength). They showed the quantum yield (QY) of ~80 % and their coating on the SiNX film textured p-type silicon solar-cells enhanced the EQE of ~30 % at 300~450 nm in wavelength, thereby enhancing the short circuit current density (JSC) of ~2.23 mA/cm2 and the PCE of ~1.08 % (relatively ~6.04 % increase compared with the reference without QDs for p-type silicon solar cells). In particular, the PCE peaked at a specific coating thickness of the Cd0.5Zn0.5S/ZnS core/shell QDs layer; i.e., the 1.08 % PCE enhancement at the 8.8 nm thick QDs layer. Last, flexible ultra-thin silicon (~30-μm thickness) solar cells implemented with an EDS layer showed stable flexible and twistable characteristics. In particular, spin-coating Cd0.5Zn0.5S/ZnS core/shell QDs on the cells enhanced the PCE by ~0.7 % through an EDS effect that enhanced the EQE at the UV light region. In addition, the cells demonstrated excellent bending fatigue performance since their PCE levels were sustained at ~12.4 % after 5000 bending cycles under ~5.72 % strain. Consequently, we demonstrated mechanism of EDS via CdSe/ZnS and Cd0.5Zn0.5S/ZnS core/shell QDs and effect of EDS layer on p-type silicon solar cells. Also, we developed low-cost and flexible ultra-thin silicon solar cell Implemented with EDS via Cd0.5Zn0.5S/ZnS core/shell QDs.