The discovery of quantum dots (QDs) earned a Nobel Prize and has led to widespread applications in research and technology. In this review, we focus on the use of QDs in solid-state solar cells (QDSCs). We begin with an overview of the basic principles of SCs. Then, we discuss how device architecture has developed over recent decades, setting the stage for the final section on fourth-generation solar cells (Perspective section). We also highlight progress in material development, starting with lead- and cadmium-based QDs and progressing to more recent carbon- and perovskite-based QDs. Additionally, we review materials used for electron-transport layers (ETLs) and hole-transport layers (HTLs). The articles also present recent advances in QDSCs across various QD types. In the final section, we recommend that future research focus on three main areas: QD active-layer materials, material interfaces, and device architecture. These efforts could lead to sustainable QDSCs that potentially surpass the Shockley–Queisser (SQ) limit.

This study highlights a purpose-driven design and optimization of a C₂N-based solar cell structure using the SCAPS-1D solar cell simulator. We investigate the performance characteristics of an ITO/MZO/C₂N/CZT heterojunction stack, focusing on optimizing the Magnesium Zinc Oxide (MZO) Electron Transport Layer (ETL), the C₂N absorber, and the CZT Hole Transport Layer/Back Surface Field (HTL/BSF). By systematically varying critical parameters such as ETL thickness, absorber thickness, and doping densities, along with interface characteristics and operating temperature, we engineer a device that achieves a peak simulated power conversion efficiency (PCE) of 32.20%. The optimized configuration yields impressive performance metrics, including V_oc = 1.605 V, J_sc = 22.927 mA/cm², and FF = 87.48%. These results highlight the significant impact of meticulous layer engineering, especially with regard to the ETL and BSF, on achieving ultra-high efficiencies in C₂N photovoltaics.