Dual enhancement of light harvesting in lead sulfide colloidal quantum dot solar cells through a three-dimensional moth-eye structure

• Dual optical enhancement in PbS CQDSCs using a 3D moth-eye structure. • Moth-eye structure reduces Fresnel reflection and boosts light absorption by 15%. • Diffraction tuning enhances NIR absorption (760–900 nm) by up to 60 %. • Experimentally confirmed 11 % increase in J sc under AM 1.5 G, 34 % under NIR. • Strategy addresses high refractive index and low NIR absorption of PbS QDs. Efficient light harvesting is crucial for the near-infrared (NIR) lead sulfide (PbS) colloidal quantum dot solar cells (CQDSCs), an emerging photovoltaic technology with broad-band solar light absorption, high stability, solution processability, and high theoretical efficiency. However, achieving high light harvesting of PbS CQDSCs is still challenging because of the intrinsic high refractive index and insufficient NIR absorption coefficient of PbS quantum dots (QDs). Here, we demonstrate a dual-enhancement strategy that utilizes a three-dimensional (3D) ZnO with sub-wavelength moth-eye structure to achieve broad-band anti-reflection and NIR optical trapping simultaneously. The optical simulation proved that this strategy could create a refractive index gradient to significantly reduce Fresnel reflection over a wide wavelength range, and generate light diffraction enhancement near the low light-absorbing band of PbS QDs. The fitting results show the simulated light harvesting ability of solar cells could be enhanced by up to 15 % due to the light reflection reduction, especially that at 760–900 nm, which could be further improved by 60 % due to the diffraction effect. The effect of this dual-enhancement strategy was experimentally examined by constructing ZnO using the microsphere template method, which increased the current density of PbS CQDSCs by 11 % under AM1.5G illumination and by 34 % under NIR illumination (>760 nm).