All-perovskite multijunction solar cells are one of the important candidates for future photovoltaic devices with high energy conversion efficiency. In the case of double-junction solar cells, it is crucial to improve the performance of the top cell. In this study, we integrated a highly efficient FAPbI3 perovskite wide-bandgap top cell with Sn-Pb mixed perovskites as a narrow-bandgap (NBG) bottom cell, as a spectral splitting four-terminal system enabling a broader WBG-NBG pairing compared to two-terminal architectures. Using the spectral splitter with a cutoff wavelength of 775 nm, a maximum power conversion efficiency (PCE) of 30.2% was accomplished. These results highlight the strong potential of mechanically stacked double-junction perovskite solar cells for further efficiency improvements.

The performance of perovskite solar cells (PSCs) depends on the quality of the perovskite absorber layer. In this study, oleic acid (OA) and oleylamine (OAm) ligand-capped formamidinium lead iodide (FAPbI3) nanoparticles (NPs) were incorporated into the formamidinium iodide (FAI) solution, which is one of the precursors for the sequential deposition of the FAPbI3 layer. The synergistic effect of the FAPbI3-NPs and the capped ligand substantially improves the crystallinity, uniformity, and morphology of the bulk FAPbI3 perovskite films. The enhancements lead to a reduction in charge recombination and a boost in charge transfer efficiency, enabling the optimized PSCs to achieve a remarkable peak power conversion efficiency (PCE) of 25.68%. Moreover, these PSCs show good stability, with unencapsulated devices maintaining 93% of the peak performance under ambient air (RH 50%) for 1000hours.

Perovskite solar cells (PSCs) have emerged as one of the most promising next-generation photovoltaic technologies due to their high power conversion efficiency (PCE) and low fabrication costs. Among various perovskite compositions, single-cation FAPbI 3 perovskites have demonstrated superior performance owing to their ideal bandgap (1.48 eV), high charge carrier mobility, and improved phase stability. However, the commercialization of FAPbI 3 -based PSCs is hindered by intrinsic phase instability and environmental degradation, which lead to the undesirable transition from the photoactive cubic α-phase to the non-perovskite δ-phase. Thus, developing strategies to stabilize the α-phase while enhancing the crystallinity and defect passivation of the perovskite films is crucial for advancing PSC technology. In recent years, perovskite nanoparticles (NPs) have been explored as promising additives to improve the quality and stability of perovskite films. The inclusion of ligand-capped perovskite NPs can facilitate grain growth, reduce defect states, and enhance moisture resistance. Despite these advantages, research on the incorporation of FAPbI 3 -NPs into FAPbI 3 bulk perovskite films remains limited. In this research, we introduce OA/OAm ligand-capped FAPbI 3 -NPs as an additive to regulate the crystallization process and enhance the optoelectronic properties of FAPbI 3 perovskite films. By leveraging the synergistic effects of perovskite NPs and surface ligands, we achieve high-efficiency PSCs with improved stability. To fabricate the perovskite absorber layer, OA/OAm-capped FAPbI 3 -NPs were synthesized and incorporated into the FAI precursor solution, which was used in the sequential deposition of the FAPbI 3 layer. The presence of these NPs modulated the nucleation and growth of the perovskite film, promoting larger grain sizes, enhanced crystallinity, and a reduction in defect density. The OA/OAm ligands played a crucial role in surface passivation by interacting with under-coordinated lead and iodide ions, redistributing residual PbI 2 into grain boundaries, and increasing the hydrophobicity of the perovskite layer. As a result, the perovskite films exhibited improved charge carrier dynamics, reduced trap-state density, and enhanced resistance to environmental degradation. Device performance characterization revealed that PSCs incorporating FAPbI 3 -NPs achieved a peak PCE of 25.68%, with significant improvements in open-circuit voltage (V oc ), short-circuit current density (J sc) , and fill factor (FF). Stability tests conducted under ambient air conditions (50% relative humidity) showed that unencapsulated devices retained 93% of their initial efficiency after 1000 hours, demonstrating the effectiveness of the NP-based strategy in enhancing environmental durability. This study presents a novel and effective approach to improving the efficiency and stability of FAPbI 3 -based PSCs by integrating OA/OAm ligand-capped FAPbI 3 -NPs into the perovskite precursor solution. The synergistic effects of the perovskite NPs and surface ligands significantly enhance film quality, crystallinity, and charge transport properties, leading to a champion PCE of 25.68% and superior stability under ambient conditions. This work underscores the potential of nanoparticle-assisted strategies in advancing the commercial viability of perovskite photovoltaics. Figure 1

Bandgap-tunable perovskite solar cells (PSCs) are highly advantageous for constructing multijunction solar cells. Among these, double-junction four-terminal (4-T) solar cells offer significant benefits due to the absence of constraints related to current matching or the structural integration of top and bottom cells, making them an effective approach for achieving higher efficiencies. In this study, a spectral splitting system was investigated to optimize the performance of 4-T solar cells. The system incorporated a Pb-based PSC with a planar heterojunction structure as the top cell, paired with a SnPb-based PSC with an inverted structure as the bottom cell. Spectral splitting was examined across five discrete wavelengths within the 700-850 nm range to identify the optimal splitting wavelength for maximizing power conversion efficiency (PCE). Ultimately, the 4-T system achieved a peak PCE of 27.8% when employing spectral splitting at 775 and 785 nm.

Perovskite solar cells (PSCs) have demonstrated remarkable advancements, achieving power conversion efficiencies (PCEs) exceeding 26 %. A critical component in these devices is 2,2 ',7,7 '-tetrakis[N,N-di(4-methox-yphenyl)amino]-9,9 '-spirobifluorene (Spiro-OMeTAD), which serves as the conventional hole transport material (HTM) in "n-i-p" structural PSCs. However, the optimal functionality of Spiro-OMeTAD necessitates doping with lithium bis(trifluoromethanesulfonyl)imide (Li-TFSI) and 4-tert-butylpyridine (tBP), both of which introduce stability challenges. Li-TFSI is highly hygroscopic, leading to moisture-induced degradation, while tBP exhibits high volatility, compromising the long-term integrity of the hole transport layers (HTLs). Additionally, the preparation of Spiro-OMeTAD typically requires a prolonged oxidation process (8-72 h) to achieve a sufficiently oxidized state with enhanced charge transport properties. In this study, stable oleyl amine (OAm) ligand nickel oxide nanoparticles (noted as the oil-NiOx NPs) were employed as p-type dopants and instantaneous oxidization agents to accelerate the oxidation of Spiro-OMeTAD. This substitution enhances the dispersion of Li-TFSI in chlorobenzene (CB) and promotes the formation of a uniform HTL film, while simultaneously introducing an immediate oxidation pathway that markedly accelerates the oxidation of Spiro-OMeTAD. In this process, Li+ interacts with the NiOx lattice to generate Ni3+ species, which act as transient oxidizing agents and drive the rapid oxidation of Spiro-OMeTAD. Consequently, power conversion efficiency (PCE) of 24.20 % was achieved, along with enhanced stability under moisture (55 % RH), thermal (85 degrees C), and light exposure conditions, maintaining 94 %, 61 %, and 80 % of their initial efficiency after more than 800 h of continuous operation.

The efficiency and the thermal stability enhancement in tin-lead (SnPb)-based perovskite solar cells (PSCs) was investigated in this study by employing germanium iodide (GeI2) as a doping agent. The incorporation of GeI2 enhanced the performance of GeI2-doped SnPb PSCs with the highest efficiency of 21.9%. The XPS depth profiling showed unique observation; the Ge layer was only formed on the surface of the SnPb films. This layer encapsulated the SnPb films and thus prevented the perovskite films from extreme oxidation and structural and morphological degradations. An interlayer engineering approach was adopted in order to prove the PSCs by employing MeO2PACz monolayer as the hole extraction layer, while the tin oxide (SnOx) layer fabricated via atomic layer deposition (ALD) was applied near the electron transport layer. More than 94% of the initial efficiency was retained after 1000 h of a thermal stability test conducted at 85 degrees C in nitrogen atmosphere in the champion device.

The spectral splitting system is one of the hybridization method to convine different solar cells to improve energy conversion efficiency by dividing sunlight into different spectral ranges. This technique is particularly valuable because different materials exhibit distinct spectral responses. By employing multiple types of solar cells optimized for different parts of the solar spectrum, overall panel efficiency can be increased compared to using a single type of solar cell. Implementing this technique requires careful design and engineering to ensure efficient spectral splitting and maximize electricity output from each type of solar cell. The organometal halide perovskite solar cell (PSC) exhibits a wide range of adjustable band gaps depending on its composition. To attain high efficiency in two-junction PSCs, combination of "mesoscopic" Pb-PSC with an "inverted" Sn-Pb mixed PSC is useful approach. In this study, a four-terminal spectral splitting double junction solar cell was fabricated by combining a mesoscopic-structure Pb-PSC and an inverted-structure Sn-Pb PSC, employing a dichroic mirror to split incident light into long and short wavelengths. In the experimental setup for the wide-bandgap top cell, initial steps involved the fabrication of compact and mesoscopic structure tin oxide layers on an FTO substrate. Subsequently, several wide-bandgap perovskite absorbers were spin-coated. Then, Spiro-OMeTAD was spin-coated onto the absorber layer, followed by thermal evaporation of gold. For the fabrication of the narrow-bandgap inverted PSC, a layer of PEDOT:PSS was spin-coated onto the FTO substrate. Then several narrow-bandgap perovskite absorbers were spin-coated. Finally, fullerene, bathocuproine, and silver were thermally evaporated onto the substrate. Finally, a four-terminal spectral splitting tandem solar cell was fabricated by combining the wide-bandgap mesoscopic structure top cell and the narrow-bandgap inverted structure bottom cell. J-V measurements conducted at several split wavelengths revealed a photovoltaic conversion efficiency (PCE) of over 20% for the top cell and about 5% for the bottom cell was obtained. However, the result showed that there is still room for improvement in bottom cell performance. As a result, the bandgap of narrow-bandgap perovskite was reduced by adjusting the ratio of tin and lead such as Cs0.025FA0.475MA0.5Sn0.6Pb0.4I3. This adjustment extended the optical absorption region of bottom cell to slightly longer wavelengths, as measured by EQE. Subsequently, the J-V measurements revealed a photovoltaic conversion efficiency of 20.1 % for the top cell and 5.36 % for the bottom cell at the 801 nm split. The total PCE of 25.5 % was obtained, surpassing previous results.

The efficiencies of the tin-lead (SnPb) perovskite solar cells (PSCs) with equimolar ratio (1:1) of tin (Sn) and lead (Pb) have reached over 23%. However, their stabilities are still being questioned which left these solar cells still behind in term of commercialization. There are several approaches such as doping, interfacial and interlayer engineering that has been introduced in order to enhance the efficiency and the stability of the SnPb PSCs. However, there is still a large gap between their achievement compared to their Pb based PSCs counterpart. In this work, we will demonstrate a structural partitioning technique which was achieved in-situ and can be applied in order to enhance the efficiency and the stability of the SnPb based PSCs. We introduced germanium (Ge) as a dopant that interestingly only formed on the surface of the SnPb film as evident from depth-profiling XPS experiment. The self-assembled monolayer (SAM) was used as the hole extraction layer instead of the conventional PEDOT:PSS hole transport layer (HTL). With this achievement, we are able to partition the SnPb PSCs by creating a physical boundary between the bottom and the top interfaces of the SnPb perovskite film. This physical boundary hindered the ion migration towards the electron transport layer (ETL) and also mitigated the formation of oxidized Sn4+ species. The SAM improved the stability as less corrosive and unreacted layer was used as the replacement unlike the PEDOT:PSS. Further, SnOx layer was coated via atomic layer deposition (ALD) near the ETL side. We also found that, the Ge layer helps to prevent the damage due to ALD process and ultimately improved the overall efficiency and the stability of the SnPb PSCs. Efficiency over 21% and retainment of more than 94% after 1000 hours of thermal test at 85°C has been achieved.

This study is on the enhancement of the efficiency of wide bandgap (FA 0.8 Cs 0.2 PbI 1.8 Br 1.2 ) perovskite solar cells (PSCs) used as the top layer of the perovskite/perovskite tandem solar cell. Poly[bis(4‐phenyl) (2,4,6‐trimethylphenyl) amine] (PTAA) and the monomolecular layer called SAM layer are effective hole collection layers for APbI 3 PSCs. However, these hole transport layers (HTL) do not give high efficiencies for the wide bandgap FA 0.8 Cs 0.2 PbI 1.8 Br 1.2 PSCs. It is found that the surface‐modified PTAA by monomolecular layer (MNL) improves the efficiency of PSCs. The improved efficiency is explained by the improved FA 0.8 Cs 0.2 PbI 1.8 Br 1.2 film quality, decreased film distortion (low lattice disordering) and low density of the charge recombination site, and improves carrier collection by the surface modified PTAA layer. In addition, the relationship between the length of the alkyl group linking the anchor group and the carbazole group is also discussed. Finally, the wide bandgap lead PSCs ( E g = 1.77 eV) fabricated on the PTAA/monomolecular bilayer give a higher power conversion efficiency of 16.57%. Meanwhile, all‐perovskite tandem solar cells with over 25% efficiency are reported by using the PTAA/monomolecular substrate.

In comparison to monolithic perovskite/perovskite double-junction solar cells, a four-terminal spectrum-splitting system is a simple method to obtain a higher power conversion efficiency (PCE) because it has no constraints of unifying the structures of the top and bottom cells. In this work, utilizing the fact that low-bandgap Sn-Pb bottom cells work the best in p-i-n while Pb-based wide-bandgap top cells work better in an n-i-p architecture, a wide-bandgap (Eg = 1.61 eV) perovskite solar cell with a mesoscopic structure and a narrow-bandgap (Eg = 1.27 eV) perovskite solar cell with an inverted structure were combined to fabricate a double-junction four-terminal spectral splitting solar cell. The double-junction solar cell with the 801 nm spectral splitting with an active area of 0.18 cm2 was found to work with a PCE of 25.3%, which is the highest reported so far for a 4-T all-perovskite double-junction spectral splitting solar cell.

Organometal halide perovskites have captured wide interest as a promising material for light-weight and high-efficiency solar cells. Through recent studies of the organometal halide perovskite solar cells (PSCs), the composition of organometal halide perovskites is recognized as one of the key factors in the improvement of the PCE. In this study, we investigated mixed cation perovskite absorber. Additionally, we successfully constructed monolithic PSC mini-module without I-V hysteresis. In the case of MA-free PSCs, the 24.9% PCE (0.187 cm2) and 21.6% PCE (2.76 cm2 monolithic PSC mini-module) were obtained, respectively. We also developed semitransparent perovskite top cells with higher durability and transmittance for tandem solar cells. The PCEs of 19.5% (certified 19.3%) and 26.2% were achieved for a 1 cm2 semi-transparent perovskite top cell and four-terminal PSC/CIGS tandem solar cells, respectively.

Ionic liquids and poly(ionic liquid)s act as bulk and/or passivation agents when used as additives in methylammonium-free lead perovskites, leading to devices showing enhanced power conversion efficiencies, reduced hysteresis and improved stability.

Herein, a comparative study of the performance of photo-storage systems based on three different solar cell technologies in combination with symmetric non-volatile supercapacitors were performed under different irradiation conditions. Photovoltaic performance was compared using current-voltage (IV), maximum power point tracking (MPPT), and charging of supercapacitor directly or through a DC-DC converter. Among the solar cells, single perovskite solar cell (PSC) was able to show better power delivery efficiencies (PDEs) and supply the required minimum operating voltage for the DC-DC boost converter at 1-20 mW.cm-2 where two series solar cells are required for dye-sensitized (DSCs) and crystalline silicon solar cells (Si-SCs). The overall efficiencies for the DC-DC boost converter charging were dropped towards low intensities from 9 to 5% and 8.5 to 2.7% for PSCs and crystalline Si-SCs, respectively. This drop was mainly due to the loss of converter efficiency at low input powers which could be negligible on large-scale solar cells. Furthermore, in direct charging, PSC provides over 8.5% stable overall efficiencies with about 80% storage efficiency under white LED light intensities ranging from 1 to 20 mW.cm-2 at the areal discharge were able to maintain high overall peak efficiencies of 5.6 and 4.1% at high areal discharging currents of 18 and 30 mA.cm-2, respectively. This study clearly demonstrates the suitability of photo-supercapacitor systems combining PSCs and carbon-based supercapacitors for continuous power-ups of indoor high current requirement IoT devices.

Tandem solar cells that combine perovskite (PVK) top cells and Si, Cu(In,Ga) (Se,S)(2) (CIGS), and other bottom cells have attracted much attention for increasing the efficiency of solar cells. To use the PVK solar cells as the top cells, their metal electrode needs to be replaced with a transparent conductive layer such as indium tin oxide (ITO) deposited by sputtering, where thermally evaporated MoOx needs to be introduced to protect the underlying hole transport layer (HTL) from sputtering damage. In this study, it was revealed that the effect of ion bombardment during ITO sputtering on widely used spiro-OMeTAD was not detrimental to the device performance, whereas it improved the power conversion efficiency (PCE) owing to the better band alignment caused by oxidation of the HTL. By eliminating the use of the MoOx buffer layer, we were able to develop semi-transparent PVK cells with higher durability and transmittance. PCEs of 19.5% (certified 19.3%) and 26.2% were achieved for a 1 cm(2) buffer-free semi-transparent PVK cell and four-terminal PVK/CIGS tandem solar cells, respectively.

Organometal halide perovskites (OHPs) have garnered considerable attention as materials for next-generation solar cells. Although the power conversion efficiencies of solar cells with OHPs are comparable to those of the existing solar cells, their durability must be improved for practical use based on a deep understanding of their basic properties. During the last decade, various methods, such as composition control, alkali metal doping, and surface passivation, were used to increase the durability of OHPs. In this study, the effects of K-doping on the thermal stability of mixed OHPs are investigated. The activation energies of the mixed OHPs with and without K-doping are found to be 128.4 +/- 5.2 and 92.9 +/- 9.8 kJ/mol, respectively. Furthermore, the Johnson-Mehl-Avrami model is adopted to the in situ X-ray diffraction measurement data, the results of which indicate that K-doped OHPs can be stabilized to such an extent that they do not decompose after 10,000 h of heating at 85 degrees C.

The efficiency of tin perovskite solar cells (TPSCs) decreases largely with increased cell area because of the inhomogeneity of the tin perovskite films formed by a one-step deposition method. Here, we apply a two-step deposition method that is rarely used in TPSCs to solve this problem. We study the steric hindrance of four different solvent molecules in the second step on the crystallization process of tin perovskites and find that the increased steric hindrance to hydroxyl in solvent molecules contributes to dense and homogeneous tin perovskite films. In comparison to the films fabrication by a one-step deposition, the tin perovskite films fabricated by the two-step deposition exhibit a higher uniformity in both the horizontal and longitudinal directions. As a result, over 10% power conversion efficiency of TPSCs was achieved with a cell size of over 1 cm2. The cell maintained over 92% of its initial efficiency after operation under 1 sun illumination for 1000 h.

The rapid development of the Internet of Things (IoTs) demands self-powered indoor devices to supply continuous power. Thus, developing an efficient photo-storage device that is capable of harvesting and storing indoor light energy requires detailed performance analysis of suitable solar cells. Herein, a comparative study of the performance of photo-storage systems based on three different solar cell technologies in combination with symmetric non-volatile supercapacitors was performed. Considering the advantages of hybrid solar cells such as low-cost fabrication and high photovoltaic response under diffused light, perovskite solar cells (PSCs) and dye -sensitized solar cells (DSCs) were selected, and the photo-storage efficiencies were compared with crystalline silicon solar cells (crystalline Si-SCs) under outdoor (Xe light irradiation: 1-100 mW cm(-2)) and indoor white Light Emitting Diode (LED) (1-20 mW cm(-2)) illumination. Photovoltaic performance was compared using current-voltage (IV), maximum power point tracking (MPPT), and charging of supercapacitor, either directly or through a DC-DC converter. The highest efficiencies were observed with PSCs under low light intensity, using Xe light and white LED light conditions. Despite the anomalous hysteresis behavior, IV analysis of the PSCs showed efficiency above 12% under Xe light irradiation and above 20% using white LED lighting (extracted from the reverse scan and at light intensity intervals of 1-20 mW cm(-2)). The determination of real-time efficiencies at MPP for PSCs showed a temporary efficiency drop at each intensity under white LED light, which is more significant for longer illumination times. However, under low light-intensity, single PSCs showed only a slight average voltage drop of 800 to 700 mV in comparison with a considerable drop of 800 to 500 mV at MPP for two series-connected crystalline Si-SCs. In addition, single PSC was able to show better power delivery efficiencies (PDEs) and supply the required minimum operating voltage for the DC-DC boost converter at 1-20 mW cm(-2) where two series solar cells are required for DSCs and crystalline Si-SCs. The overall efficiencies for the DC-DC boost converter charging dropped towards low intensities from 9 to 5% and 8.5 to 2.7% for PSCs and crystalline Si-SCs, respectively. This decrease was mainly due to the loss of converter efficiency at low input powers which could be negligible on large-scale solar cells. Furthermore, in direct charging, PSC provided over 8.5% stable overall efficiencies with about 80% storage efficiency under white LED light intensities ranging from 1 to 20 mW cm-2 at the areal discharge, and were able to maintain high overall peak efficiencies of 5.6 and 4.1% at high areal discharging currents of 18 and 30 mA cm(-2), respectively. This study demonstrates the suitability of photo-supercapacitor systems combining PSCs and carbon-based supercapacitors for continuous power-up of indoor high-current-requirement IoT devices.

According to the detailed balanced limit for a single-junction solar cell, tin-lead (Sn-Pb) perovskite solar cells (PSCs) can achieve power conversion efficiencies (PCEs) more than Pb-PSCs. However, the rise in PCE of Sn-Pb PSCs is limited by the choice of hole transport layer to PEDOT:PSS only. Inspired by the use of hole selective monolayers (HSM) in Pb only PSCs, here, we employed 2-(9H-carbazol-9-yl) ethyl] phosphonic acid (2PACz), leading to PCE (21.39%) comparable to PSCs fabricated on conventional PEDOT:PSS (21.37%). Moreover, we reported a small molecule, methyl phosphonic acid (MPA), employing which an equipotential performance (PCE= 21.08%) was obtained owing to its passivation effect on the transparent conducting oxide (TCO) layer. Furthermore, by taking motivation from the idea of cosensitization in dye sensitized solar cells, we explored the point that the coabsorption of 2-(9H-carbazol-9-yl) ethyl] phosphonic acid (2PACz) and a small molecule MPA on TCO glass led to the Sn-Pb PSC (1.25 eV) with a PCE of 23.3% and open-circuit voltage of 0.88 V.

A sodium chloride modification was applied where different amounts of sodium chloride was physically blended in a tin oxide colloid solution to passivate the interface between the electron transport layer (ETL) and perovskite layer and improve the performance of perovskite solar cells. Sodium chloride-modified tin oxide was utilized as the electron transport material to fabricate perovskite solar cells. It was found that sodium chloride-modified tin oxide as an ETL could considerably enhance the performance of the device compared to pristine tin oxide. The power conversion efficiency of the perovskite solar cell displayed 8.8% remarkable improvement from 18.7 ± 0.4% to 20.3 ± 0.3% on average and 9.5% improvement from 18.9 to 20.7% in champion devices because of the considerable enhancement of the fill factor when 25 mM sodium chloride-modified tin oxide as the ETL was used in comparison with pristine tin oxide.