The antireflection coating (ARC) suppresses surface light loss and thus improves the power conversion efficiency (PCE) of solar cells, which is its essential function. This paper reviews the latest applications of antireflection optical thin films in different types of solar cells and summarizes the experimental data. Basic optical theories of designing antireflection coatings, commonly used antireflection materials, and their classic combinations are introduced. Since single and double antireflection coatings no longer meet the research needs in terms of antireflection effect and bandwidth, the current research mainly concentrates on multiple layer antireflection coatings, for example, adjusting the porosity or material components to achieve a better refractive index matching and the reflection effect. However, blindly stacking the antireflection films is unfeasible, and the stress superposition would allow the film layer to fail quickly. The gradient refractive index (GRIN) structure almost eliminates the interface, which significantly improves the adhesion and permeability efficiency. The high-low-high-low refractive index (HLHL) structure achieves considerable antireflection efficiency with fewer materials while selecting materials with opposite stress properties improves the ease of stress management. However, more sophisticated techniques are needed to prepare these two structures. Furthermore, using fewer materials to achieve a better antireflection effect and reduce the impact of stress on the coatings is a research hotspot worthy of attention.

Quantum dot intermediate band solar cell (QD-IBSC) has high efficiency theoretically. It can absorb photons with energy lower than the bandgap of the semiconductor through the half-filled intermediate band, extending the absorption spectrum of the cell. However, issues in the IBSC, such as the strain around multi-stacking QDs, low thermal excitation energy, and short carrier lifetime, lead to its low conversion efficiency. In recent years, many efforts have been made from different aspects. In this paper, we focus on In(Ga)As QD-IBSC, list the experimental technologies used to improve the performance of the cell and review the recent research progress. By analyzing the effects of different technologies on conversion efficiency, the development direction of the In(Ga)As QD-IBSC in the future is proposed.