In the past few decades, the fabrication of solar cells has been considered as one of the most promising ways to meet the increasing energy demands to support the development of modern society as well as to control the environmental pollution caused by the combustion of fossil fuels.

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The elemental proportion of Cu poor and Zn rich in Cu2ZnSn(S,Se)4 (CZTSSe) is well established for achieving highly efficient CZTSSe solar cells. However, how high Zn/Sn ratio can the complicated CZTSSe thin film tolerate remains a question. Therefore, herein, the well control of Zn/Sn ratio in CZTSSe thin film is obtained by multi‐spin‐coating and tuning the initial Zn/Sn ratio in the Cu–Zn–Sn–S precursor ink from 1.0 to 1.9. It is found that the Zn/Sn on the surface of CZTSSe absorber can self‐regulate to around 1.2 even with Zn/Sn ratio up to 1.9 in the precursor solution. Excess Zn presented as Zn(S,Se) secondary phase not only concentrate near the bottom area, but also widely distribute at the grain boundaries (GBs). In addition, it is found that the Zn(S,Se) secondary phase at GBs can promote current transport as revealed by conductive atomic force microscopy measurement. The surface roughness and grain size of the resulting CZTSSe absorber increased, whereas the MoSe2 thickness was reduced with increasing Zn/Sn ratio. More importantly, the device performance increased from 4.5% to 10.0% with a significant decrease in VOC deficit from 0.73 to 0.58 V when the Zn/Sn ratio increases from 1.0 to 1.5 in the precursor ink.

Perovskite solar cells (PVSCs) are the most promising candidates in third-generation photovoltaic technologies with a certified efficiency of 25.2% within the past decades. They attract increasing attention owing to their ease of fabrication, cost-effectiveness, and lower processing temperature when compared to commercial silicon-based solar cells. However, some of the striking disadvantages including the low stability, toxicity of the lead element, and hysteresis effect limit the photovoltaic performances and commercialization of the PVSCs. Furthermore, the insufficient utilization of the solar spectrum in commonly used PVSCs due to the spectral mismatch between the solar spectrum and the bandgap of the perovskite is an obstacle to improving the efficiencies of PVSCs. In this regard, lanthanide-doped luminescent materials are implemented in PVSCs for the conversion of a broad spectrum of light into photons of resonant wavelengths through upconversion (UC), downconversion (DC), and downshifting (DS) processes, which are employed to decrement the losses in the energy conversion processes of solar cells. Interestingly, the lanthanide-based UC/DC processes facilitate improved sensitization, light scattering, and stability in PVSCs. Moreover, the lanthanide ions are directly doped into transporting layers for tuning the band alignment, which is an efficient way to enhance the charge carrier transportation, and it is desirable to enhance the power conversion efficiency (PCE) of devices. In this review article, the insights for various UC and DC materials in PVSCs are discussed. Finally, the challenges with emerging research directions are mentioned for further developments of future luminescent-based PVSCs, and some perspectives for future research are also presented.

All‐inorganic perovskite of CsPbBr3 thin‐films solar cells has attracted increasing interest in recent years due to its potential long‐term stability over the generally used hybrid perovskites. Herein, all‐inorganic CsPbBr3 perovskites are doped with Eu2+ to enhance the efficiency of perovskite solar cells (PVSCs). The perovskite films exhibit a better crystallinity with smooth morphology after the introduction of rare‐earth elements. Hence, the hole‐transport layer‐free device with presence of Eu2+ and low‐cost carbon electrode achieves both enhanced efficiency and stability. In particular, the power conversion efficiency (PCE) enhances from 5.66% to 7.28% with high VOC of 1.45 V by optimizing the doping concentration of Eu2+. In addition, the storage stability measurements reveal excellent performances of PCE without encapsulation in air with relative humidity of 70–80%. These results can pave changes in future inorganic PVSCs.