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.

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.

The application of doctor-blading for flexible solar cells is considerably attractive due to its potential upscaling feasibility via roll-to-roll process. Herein, we report the fabrication of efficient flexible Cu2ZnSn(S,Se)4 (CZTSSe)...

The use of transparent conducting oxide (TCO) as a substrate in Cu 2 ZnSn(S,Se) 4 (CZTSSe) thin-film solar cells allows for advanced applications, such as bifacial, semitransparent, and tandem solar cells with the capability to increase power density generation. However, the efficiency of this kind of solar cell is still below 6% based on the low-cost solution process. In this work, we develop a composition gradient strategy and demonstrate a 6.82% efficient CZTSSe solar cell on F:SnO 2 (FTO) substrate under the ambient condition. The composition gradient is realized by simply depositing the precursor inks with different Zn/Sn ratios. To verify that the high performance of the solar cell is attributed to the composition gradient strategy rather than the sole change of the Zn/Sn ratio, devices based on absorbers with varied Zn/Sn ratios are fabricated. Furthermore, the structure and surface morphology of the CZTSSe films with/without composition gradients are examined. The presence of elemental gradient through the depth of the CZTSSe films before and after annealing is confirmed by secondary ion mass spectroscopy analysis. It is found that the composition gradient enhances the crystallinity of the absorber, reduces the surface roughness as well as device parasitic losses, contributing to a higher fill factor, open-circuit voltage , and conversion efficiency.

Flexible Cu2ZnSn(S,Se)4 (CZTSSe) solar cells have attracted considerable attention due to their potential application in specific areas such as power sources for wearable electronics. However, the over‐thick Mo(Sx,Se1−x)2 at the back contact is one of the factors that limit the device performance. Herein, a facile strategy to inhibit the thick Mo(Sx,Se1−x)2 layer by adding a proper proportion of sulfur during selenization is reported. It is found that the thickness of Mo(Sx,Se1−x)2 can be effectively tailored via tuning the proportion of S, enabling a substantial decrease in series resistance. The suppression mechanism is mainly ascribed to the change of orientation of Mo(Sx,Se1−x)2 induced by S, which limits the diffusion of Se to Mo. Accordingly, the total area efficiency of the flexible CZTSSe device improves significantly from 5.5 to 8.9% with the addition of 2% S, followed by a drop with more S. Furthermore, it is demonstrated that this strategy can also be applied to both kesterite and chalcogenide absorbers deposited on rigid Mo substrates to suppress the thick Mo(Sx,Se1−x)2 layer, indicating the universality of this method. Overall, this work provides a general, facile, and effective approach to modify the back contact interface without introducing extra blocking layers.

The effects of ultrasonic frequencies on both the mass transport process and diffusion layer were investigated during electrochemical treatment. The rates of mass transfer at a stainless steel cathode were measured for copper and lead in dilute acidified copper sulphate and lead nitrate solutions at different ultrasonic frequencies. Concentrations in bulk solution were determined by atomic absorption spectrophotometer. By increasing frequencies from 40 to 100 kHz, a high value for the mass transfer coefficient and an effective thinning of the diffusion layer were observed. Higher rates of mass transfer reduced energy consumption. Use of ultrasound with electrochemical processes can provide valuable contributions to remove metallic ions from industrial wastewater without using extra chemicals. The process has efficiently reduced the cost of energy consumption and deposition time.

The use of transparent conducting oxides (TCO) as a back contact for Cu2ZnSn(S,Se)4 (CZTSSe) thin film solar cell enables light absorption from both front and rear sides and allows for the fabrication of semi‐transparent photovoltaic devices. However, the CZTSSe solar cell based on TCO substrate suffers from high parasitic losses owing to the long post‐annealing time at elevated temperature required for high‐quality absorber. This work aims to overcome this issue by carefully tailoring the annealing conditions to obtain high‐performance solar cell. Rapid thermal processing is used to instantaneously generate high Se vapor pressure at target temperature and shorten the annealing time. The crystalline quality, morphology, and particularly the photovoltaic performance of the resulting CZTSSe thin film are systematically investigated. It is found that the increase of annealing temperature and time improves the crystalline quality but unfortunately deteriorates the device performance owing to increasing parasitic losses. Increasing the amount of Se allows to get highly crystalline absorber within 7 min of annealing, yielding a total area 5.56% efficient CZTSSe solar cell with front illumination resulting from reducing parasitic losses. This work provides a simple approach to preserve the back contact without using a complex interfacial layer.