Enhancement Of Open-circuit Voltage Research Articles

A comprehensive study on passive cooling of a PV device using PCM and various fin configurations: Pin, spring, and Y-shaped fins

This study addresses the need for effective passive cooling strategies in compact photovoltaic (PV) modules by exploring three distinct fin shapes—pin fin, Y-shaped fin, and spring fin—utilizing both numerical simulations and experiments. The objective is to enhance heat transfer rates in PV devices through extended surfaces and phase-change material (PCM). Departing from conventional approaches like metal foams and plate fins that contribute to increased weight and system complexity, the research employs the finite volume method in computational fluid dynamics for numerical simulations, validated with experimental data. Comparative scenarios include fins with the same cross-sectional area and the same volume, revealing that the pin fin configuration outperforms others significantly. An experimental focus on pin fin numbers and lengths demonstrates a remarkable 9 °C temperature reduction with fully saturated pin fins, translating to a 4 % increase in efficiency and a noteworthy 0.8 V enhancement in open-circuit voltage. The findings underscore the potential of this proposed PV-PCM passive cooling approach for achieving performance enhancements while being easily constructed at a lower cost, providing a cost-efficient solution with clear quantitative results indicating temperature reduction, efficiency improvement, and enhanced voltage.

Simultaneous enhancement of photocurrent and open circuit voltage in ternary organic solar cells by red fluorescent material as third component materials

Ternary organic solar cells (OSCs) were constructed using D18-Cl:Y6 as the host photoactive layer and the red fluorescent material [4-(dicyano-methylene)-2-methyl-6-(p-dimethyl aminostyryl)-4H-pyran] (DCM) as the third component material. The optimized ternary OSCs (optimized weight ratio of D18-Cl:Y6:DCM is 1:1.4:0.1) showed a power conversion efficiency (PCE) of 17.36 %, a short-circuit current density (JSC) of 26.79 mA cm−2, an open-circuit voltage (VOC) of 0.89 V, and a fill factor (FF) of 72.8 %. Since the absorption peak of DCM is located in the red light region and the photoluminescence peak of DCM is covered by the absorption peak of D18-Cl, DCM significantly improves the short-wavelength light absorption of the optimized ternary photoactive layer and facilitates the energy transfer from DCM to D18-Cl. While increasing the DCM content, the LUMO level of the blend acceptor is shifted upwards, which favors the VOC value. However, excessive amount of DCM would damage the phase separation, bulk and surface morphology of the ternary film. The results showed that the red fluorescent material DCM has great potential as a third component material for realizing highly efficient ternary OSCs.

Bridging the buried interface with conjugated molecule for highly efficient carbon-based inorganic CsPbI2Br perovskite solar cells fabricated in air

Manipulating the buried interface of all-inorganic perovskite solar cells (PSCs) is essential to improve the performance of devices. However, the conventional modifiers of interface typically present insulating feature that can impede the transportation of carrier, leading to an inferior charge transport efficiency. Herein, we propose a conjugated molecule, 2,4-hexadienoic acid potassium salt, which can act as a bridge at the buried interface of device and improve the crystallization of perovskite film. Besides, this interfacial modifier also promotes larger and denser grains, passivating defects and suppress non-radiative recombination of buried interface. Simultaneously, the electrical performance of tin oxide film is enhanced and facilitate a better energy level alignment. Consequently, carbon electrodes-based PSCs (C-PSCs) are fabricated via a hot air-assisted method in air, and C-PSCs based on all-inorganic perovskite demonstrate significant enhancement of open circuit voltage (1.25 V) via conjugated molecule modification, and the power conversion efficiency (PCE) increase significantly from 10.86 % to 13.11 %. Moreover, unencapsulated target devices exhibit better stability than the control devices. This work offers a new idea to construct an interfacial bridge via conjugated molecule for efficient and stable C-PSCs fabricated in air.

Vacuum-Processed Propylene Urea Additive: A Novel Approach for Controlling the Growth of CH3NH3PbI3 Crystals in All Vacuum-Processed Perovskite Solar Cells.

In this study, we present a novel method for controlling the growth of perovskite crystals in the vacuum thermal evaporation process by utilizing a vacuum-processable additive, propylene urea (PU). By coevaporation of perovskite precursors with PU to form the perovskite layer, PU, acting as a Lewis base additive, retards the direct reaction between the perovskite precursors. This facilitates a larger domain size and reduced defect density. Following the removal of the residual additive, the perovskite layer, exhibiting improved crystallinity, demonstrates reduced charge recombination, as confirmed by a time-resolved microwave conductivity analysis. Consequently, there is a notable enhancement in open-circuit voltage and power conversion efficiency, increasing from 1.05 to 1.15 V and from 17.17 to 18.31%, respectively. The incorporation of a vacuum-processable and removable Lewis base additive into the fabrication of vacuum-processed perovskite solar cells offers new avenues for optimizing these devices.

Orientation Manipulation and Defect Passivation for Perovskite Solar Cells by a Natural Compound.

Different facets in perovskite crystals exhibit distinct atomic arrangements, influencing their electronic, physical, and chemical properties. Perovskite films incorporating tin oxide (SnO2) as the electron transport layer face challenges in facet regulation. This study reveals that tea saponin (TS), a natural compound serves as a SnO2 modifier, facilitates optimal growth of perovskite crystals on the (111) facet. The modification promotes preferential crystal orientation through hydrogen bond and Lewis coordination. TS forms a chelate with SnO2, resulting in a smoother film and n-type doping, leading to improved carrier extraction and reduced defects. The TS-modified perovskite solar cells achieve a champion efficiency of 24.2%, leveraging from an obvious enhancement of open-circuit voltage (Voc) of 1.18V and fill factor (FF) of 82.8%. The devices also demonstrate enhanced humidity tolerance and storage stability, ensuring improved stability without encapsulation.

Investigation on the diffusion mechanism of Ga element and regulation of the V-shaped bandgap in CIGS thin films based on magnetron sputtering with a quaternary target

Gradient bandgap engineering has been acknowledged as an effective approach for improving the efficiency of CIGS solar cells. However, an effective method for achieving gradient bandgap engineering in quaternary sputtered CIGS films has not yet been identified.This is due to the uniform and singular nature of the quaternary target composition, as well as the complex kinetic mechanisms that result in the rearrangement of film elements (particularly Ga) during the annealing process. In this study, a grain boundary migration-driven diffusion mechanism for the Ga element in CIGS thin films was established to address the presented issue. The segregation of Ga element is believed to be caused by the flow velocity field generated from the migration of grain boundaries, and the distribution of Ga element can be precisely calculated using the mass transport equation. By modulating the V-shaped bandgap, a notable enhancement in open-circuit voltage (Voc) was achieved, with an increase from 0.405 V to 0.515 V, leading to an effectively improvement of solar cell's efficiency. By comparing and analyzing the actual performance parameters of the solar cells and the simulated results, we conclude that the increase in Voc is due to the alteration in bandgap structure. This study presents a novel approach to bandgap engineering in quaternary sputtered CIGS films through the quantitative calculation of Ga element distribution.

Self-Assembled Molecules with Asymmetric Backbone for Highly Stable Binary Organic Solar Cells with 19.7 % Efficiency.

The hole-transporting material (HTM), poly (3,4-ethylene dioxythiophene) poly(styrene sulfonate) (PEDOT : PSS), is the most widely used material in the realization of high-efficiency organic solar cells (OSCs). However, the stability of PEDOT : PSS-based OSCs is quite poor, arising from its strong acidity and hygroscopicity. In addition, PEDOT : PSS has an absorption in the infrared region and high highest occupied molecular orbital (HOMO) energy level, thus limiting the enhancement of short-circuit current density (Jsc) and open-circuit voltage (Voc), respectively. Herein, two asymmetric self-assembled molecules (SAMs), namely BrCz and BrBACz, were designed and synthesized as HTM in binary OSCs based on the well-known system of PM6 : Y6, PM6 : eC9, PM6 : L8-BO, and D18 : eC9. Compared with BrCz, BrBACz shows larger dipole moment, deeper work function and lower surface energy. Moreover, BrBACz not only enhances photon harvesting in the active layer, but also minimizes voltage losses as well as improves interface charge extraction/ transport. Consequently, the PM6 : eC9-based binary OSC using BrBACz as HTM exhibits a champion efficiency of 19.70 % with a remarkable Jsc of 29.20 mA cm-2 and a Voc of 0.856 V, which is a record efficiency for binary OSCs so far. In addition, the unencapsulated device maintains 95.0 % of its original efficiency after 1,000 hours of storage at air ambient, indicating excellent long-term stability.

Holistic dielectric and buffer interfacial layers enable high-efficiency perovskite solar cells and modules

Suppressing the interfacial non-radiative recombination plays a critical role in reducing the voltage loss of perovskite solar cells. Herein, we develop a holistic interfacial regulation using dielectric materials of Al2O3 and PEABr/PMMA, and a buffer layer of compact SnOX to manipulate the multiple interfaces. A compact SnOX is inserted to reduce the charge accumulation at the interface of electron transport layer/Ag. Through this multiple interfacial design, the power conversion efficiency is greatly increased from 22.66% to 25.70% (certified 24.23%), mainly attributing to much enhancement in open circuit voltage and fill factor. The fill factor of 86.41% is the highest among the self-assembled-monolayers-based inverted devices. Both perovskite film and resulting device show increased thermal stability due to the incorporation of compact SnOX, which inhibits the escape of volatile species from perovskite, infiltration of moisture and the suppression of ion migration. Scaling up this strategy delivers an efficiency for a minimodule as high as 21.56%. More importantly, we discovered that the PEABr passivation could induce the collapse of morphology under continuous illumination, thus leading to worse operational stability. This work provides a path towards omnibearing modification for minimizing the trap-assisted recombination at the interface through the synergetic effects of dielectric materials.

Hysteresis-free perovskite solar cells with over 24% efficiency enabled by ZnCl2 doped SnO2 electron transfer layer

Tin dioxide (SnO2) has been widely applied as the electron transport layer (ETL) in perovskite solar cells. However, the SnO2 with low conduction band minimum that has mismatched energy levels between the perovskite film and severe SnO2/perovskite interfacial defects is liable to cause nonradiative recombination. In order to modify the SnO2 layer, herein, we introduced the zinc chloride (ZnCl2) hydrochloric acid solution into the SnO2 nanocrystals solution (SnO2–Zn) and proved that ZnCl2 doping in the SnO2 ETL is a simple and low-cost passivation method, which can significantly improve the efficiency and stability of devices and remove the hysteresis. Ultimately, an enhancement of open-circuit voltage from 1.13 to 1.16 V and an increased corresponding power conversion efficiency from 22.88% to 24.12% are achieved for the devices using SnO2–Zn ETL.

Improving the performance of kesterite solar cells by solution germanium alloying.

Cation substitution is an effective strategy to regulate the defects/electronic properties of kesterite Cu2ZnSn(S,Se)4 (CZTSSe) absorbers and improve the device photovoltaic performance. Here, we report Ge alloying kesterite Cu2Zn(Sn,Ge)(S,Se)4 (CZTGSSe) via a solution approach. The results demonstrate that the same chemical reaction of Ge4+ to Sn4+ ensures homogeneous Ge incorporation in the whole range of concentrations (from 0 to unit). Ge alloying promotes grain growth and linearly enlarges the absorber band gap by solely raising the conduction band minimum, which maintains a "spike" conduction band offset at the heterojunction interface until 15% alloying concentration and thus facilitates effective charge carrier collection. A promising efficiency of 11.57% has been achieved at 15% Ge alloying concentration with a significant enhancement in open-circuit voltage and fill factor. By further 10% Ag alloying to improve the absorber film morphology, a champion device with an efficiency of 12.25% has been achieved without an antireflective coating. This result emphasizes the feasibility of achieving homogeneous and controllable Ge alloying of kesterite semiconductors through the solution method, paving the way for further improvement and optimization of device performance.

Flavonoid from Hedera helix fruits: A promising new natural sensitizer for DSSCs

Owing to their lower cost, simplicity of manufacture, environmental friendliness, and accessibility of raw materials, natural dyes emerge as the most viable substitute for dye-sensitized solar cells (DSSCs). However, the photovoltaic performance of DSSCs based on natural dyes stays behind that of their metal-based counterparts. This can be partially overcome when appropriate chemical additives are present in the redox electrolyte employed in DSSCs based on natural dyes. To determine the ideal additives for DSSCs based on natural dye extracted from Hedera helix fruits, including flavonoid pigments, we thoroughly compare the actions of 1-butyl-3-methylimidazolium iodide, guanidinium thiocyanate, and tert-butylpyridine additives in ionic liquid-based redox electrolytes. These additives suppress undesirable charge recombination and parasitic resistance effects, achieving a more significant enhancement of open-circuit voltage (Voc) of 130 mV and fill factor (FF) of 30 % compared to their counterparts. Utilizing prepared electrolyte solutions in DSSCs also presents an outstanding increase in the efficiency of the devices, from 0.75 % to 1.17 % (∼56 % improvement), which outperforms other natural dye sources containing flavonoid pigments as well. The experimental findings provided in this study demonstrate that the development of electrolytes tailored for natural dyes can lead to greater power conversion efficiency.

Enhancing the Performance of Perovskite Solar Cells by Introducing 4-(Trifluoromethyl)-1H-imidazole Passivation Agents.

Defects in perovskite films are one of the main factors that affect the efficiency and stability of halide perovskite solar cells (PSCs). Uncoordinated ions (such as Pb2+, I-) act as trap states, causing the undesirable non-radiative recombination of photogenerated carriers. The formation of Lewis acid-base adducts in perovskite directly involves the crystallization process, which can effectively passivate defects. In this work, 4-(trifluoromethyl)-1H-imidazole (THI) was introduced into the perovskite precursor solution as a passivation agent. THI is a typical amphoteric compound that exhibits a strong Lewis base property due to its lone pair electrons. It coordinates with Lewis acid Pb2+, leading to the reduction in defect density and increase in crystallinity of perovskite films. Finally, the power conversion efficiency (PCE) of PSC increased from 16.49% to 18.97% due to the simultaneous enhancement of open-circuit voltage (VOC), short circuit current density (JSC) and fill factor (FF). After 30 days of storage, the PCE of the 0.16 THI PSC was maintained at 61.9% of its initial value, which was 44.3% for the control device. The working mechanism of THI was investigated. This work provides an attractive alternative method to passivate the defects in perovskite.

Interface Modification for Efficient and Stable Inverted Inorganic Perovskite Solar Cells.

Due to their excellent thermal stability and ideal bandgap, metal halide inorganic perovskite based solar cells (PSCs) with inverted structure are considered as an excellent choice for perovskite/silicon tandem solar cells. However, the power conversion efficiency (PCE) of inverted inorganic PSCs still lags far behind that of conventional n-i-p PSCs due to interfacial energy level mismatch and high nonradiative charge recombination. Herein, the performance of inverted PSCs was significantly improved by interfacial engineering of CsPbI3-x Brx films with 2-mercapto-1-methylimidazole (MMI). It is found that the mercapto group can preferably react with the undercoordinated Pb2+ from perovskite by forming Pb-S bonds, which appreciably reduces the surface trap density. Moreover, MMI modification results in a better energy level alignment with the electron transporting material, promoting carrier transfer and reducing voltage deficit. The above combination results in an open circuit voltage enhancement by 120mV, yielding a champion PCE of 20.6% for 0.09 cm2 area and 17.3% for 1 cm2 area. Furthermore, the ambient, operational and heat stabilities of inorganic PSCs with MMI modification are also greatly improved. Our work demonstrates a simple but effective approach for fabricating highly efficient and stable inverted inorganic PSCs. This article is protected by copyright. All rights reserved.

3D Printed SnS2/SnS-Based Nanocomposite Hydrogel as a Photoenhanced Triboelectric Nanogenerator

Recent advancements in printing technologies have led to new fabrication techniques for the development of various flexible, compact, wearable, and portable energy harvesters and self-powered devices. In particular, the three-dimensional printing (3DP) technology for a nanogenerator has become advantageous due to its low cost, simplicity, and high precision in fabricating complicated structures. Therefore, we report a 3DP-based photoinduced triboelectric nanogenerator (PTNG) fabrication, a hybrid version of a conventional triboelectric nanogenerator. Here, a 3D printed poly(vinyl alcohol) (PVA) nanocomposite hydrogel (3DPH) with photoactive SnS2/SnS nanoflakes is used as a tribo-positive material and copper foil as a tribo-negative material for PTNG application. Under light illumination, the as-fabricated PTNG with an optimized weight percentage of SnS2/SnS displays the open-circuit voltage (Voc) enhancement from 29 to 37.5 V and short-circuit current (Isc) enhancement from 1.23 to 1.58 μA. In addition, the power density of the device is observed at 5.4 μW/cm2 under illumination conditions at the external load of 60 MΩ. This enhanced performance of the as-fabricated PTNG is attributed to the mutual coupling effect and improved interfacial interactions between the SnS2/SnS nanoflakes and PVA under the influence of light illumination, leading to a charge-trapping mechanism. The outstanding performance and stability of the as-fabricated PTNG surpassing all similar recent reports, establish it as an effective hybrid platform for constructing multifunctional self-powered devices.

Molecular Orientation Control of Regioisomeric Small-Molecule Acceptors for High-Performance Poly(3-hexylthiophene)-Based Organic Solar Cells with 9.3% Efficiency

Use of poly(3-hexylthiophene) (P3HT) enables low-cost manufacture of organic solar cells (OSCs). However, the power conversion efficiencies (PCEs) of the P3HT-based OSCs should be further enhanced. Herein, we report the development of noncovalently fused nonfullerene acceptors (NFAs) that realize high-performance P3HT-based OSCs (>9%). We synthesize regioisomeric NFAs (C4-In and C4-Out) in which the positions of the methyl substituents of their end groups differ. Interestingly, the molecular orientation of the regioisomers in thin film is found to change from edge-on (C4-Out) to face-on (C4-In) orientation, allowing a model study exploring the impact of the microstructure of NFAs on the performance of P3HT-based OSCs. We find that face-on oriented C4-In facilitates both electron and hole transport in a P3HT-based OSC along the vertical direction. In addition, C4-In shows reduced trap densities and suppressed charge recombination in the P3HT:C4-In OSC due to its lower energetic disorder relative to C4-Out. As a result, the P3HT:C4-In OSC (PCE = 9.35%) outperforms a P3HT:C4-Out OSC (PCE = 8.12%) owing to simultaneous enhancement in open-circuit voltage, short-circuit current density, and fill factor. This study demonstrates the importance of molecular orientation of NFAs for developing high-performance P3HT-based OSCs.

Transport Layer Engineering by Hydrochloric Acid for Efficient Perovskite Solar Cells with a High Open-Circuit Voltage

A large number of defect states that exist at the interface between a perovskite film and an electron transport layer (ETL) are detrimental to the efficiency and the stability of perovskite solar cells (PSCs). It is still a challenge to simultaneously passivate the defects on both sides by a stable and low-cost ion compound. Herein, we demonstrate a simple and effective versatile strategy by introducing hydrochloric acid into SnO2 precursor solution to passivate the defects in both SnO2 and perovskite layers and simultaneously reduce the interface energy barrier, ultimately achieving a high-performance and hysteresis-free PSCs. Hydrogen ions can neutralize -OH groups on the SnO2 surface, whereas the Cl- can not only combine with Sn4+ in ETL but also suppress the Pb-I antisite defects formed at the buried interface. The reduced nonradiative recombination and the favorable energy level alignment result in a significantly increased efficiency from 20.71 to 22.06% of PSCs due to the enhancement of open-circuit voltage. In addition, the stability of the device can also be improved. This work presents a facile and promising approach for the development of highly efficient PSCs.

Improved Carrier Management via a Multifunctional Modifier for High-Quality Low-Bandgap Sn-Pb Perovskites and Efficient All-Perovskite Tandem Solar Cells.

All-perovskite tandem solar cells (TSCs) hold great promise in terms of ultrahigh efficiency, low manufacturing cost, and flexibility, stepping forward to the next-generation photovoltaics. However, their further development is hampered by the relatively low performance of low-bandgap (LBG) tin (Sn)-lead (Pb) perovskite solar cells (PSCs). Improving the carrier management, including suppressing trap-assisted non-radiative recombination and promoting carrier transfer, is of great significance to enhance the performance of Sn-Pb PSCs. Herein, a carrier management strategy is reported for using cysteine hydrochloride (CysHCl) simultaneously as a bulky passivator and a surface anchoring agent for Sn-Pb perovskite. CysHCl processing effectively reduces trap density and suppresses non-radiative recombination, enabling the growth of high-quality Sn-Pb perovskite with greatly improved carrier diffusion length of >8µm. Furthermore, the electron transfer at the perovskite/C60 interface is accelerated due to the formation of surface dipoles and favorable energy band bending. As a result, these advances enable the demonstration of champion efficiency of 22.15% for CysHCl-processed LBG Sn-Pb PSCs with remarkable enhancement in both open-circuit voltage and fill factor. When paired with a wide-bandgap (WBG) perovskite subcell, a certified 25.7%-efficient all-perovskite monolithic tandem device is further demonstrated.

1-Adamantanamine Hydrochloride Resists Environmental Corrosion to Obtain Highly Efficient and Stable Perovskite Solar Cells.

Passivating the defective surface of perovskite film is a promising strategy to improve the stability and efficiency of perovskite solar cells (PSCs). Herein, 1-adamantanamine hydrochloride (ATH) is introduced to the upper surface of the perovskite film to heal the defects of the perovskite surface. The best-performance ATH-modified device has a higher efficiency (23.45%) than the champion control device (21.53%). The defects are passivated, interfacial nonradiative recombination is suppressed, and interface stress is released by the ATH deposited on the perovskite film, leading to longer carrier lifetimes and enhancement in open-circuit voltage (VOC) and fill factor (FF) of the PSCs. With obvious improvement, VOC and FF of 1.159 V and 0.796 for the control device are raised to 1.178 V and 0.826 for the ATH-modified device, respectively. Finally, during an operational stability measurement of more than 1000 h, the ATH-treated PSC exhibited better moisture resistance, thermal persistence, and light stability.

Suppressing non-radiative recombination in metal halide perovskite solar cells by synergistic effect of ferroelasticity

The low fraction of non-radiative recombination established the foundation of metal halide perovskite solar cells. However, the origin of low non-radiative recombination in metal halide perovskite materials is still not well-understood. Herein, we find that the non-radiative recombination in twinning-tetragonal phase methylammonium lead halide (MAPbIxCl3-x) is apparently suppressed by applying an electric field, which leads to a remarkable increase of the open-circuit voltage from 1.12 V to 1.26 V. Possible effects of ionic migration and light soaking on the open-circuit voltage enhancement are excluded experimentally by control experiments. Microscopic and macroscopic characterizations reveal an excellent correlation between the ferroelastic lattice deformation and the suppression of non-radiative recombination. The calculation result suggests the existence of lattice polarization in self-stabilizable deformed domain walls, indicating the charge separation that facilitated by lattice polarization is accountable for the suppressed non-radiative recombination. This work provides an understanding of the excellent performance of metal halide perovskite solar cells.

Enhancement of OCV and capacity by activating electrolyte with polyiodide ions towards high-availability self-charging zinc ion batteries

Self-charging zinc ion batteries (ZIBs) without integrated external power generation equipment, featuring simple configuration and strong adaptability, is considered an advanced technology to overcome acute dependence on energy sources and high selectivity on the spatiotemporal environment in the conventional self-charging system. To enable high availability for practical applications, increasing the open-circuit voltage (OCV) and capacity of the self-charging ZIBs is undoubtedly an effective route. In this study, the self-charging mechanism of the VO 2 /ZnSO 4 /Zn (VO 2 /ZS/Zn) battery was revealed as the spontaneous oxidation of discharge product HVO 2 . Accordingly, polyiodide ions were introduced to activate the ZnSO 4 electrolyte to enhance spontaneous oxidation. As a result, the OCV of the self-charging ZIB was increased from 1.15 to over 1.3 V. Further coupling with light stimulation, the self-charging capacity reached 206 mAh g −1 at 0.3 A g −1 , while the self-charging process was shortened from more than 20 h to less than 2 h. The assembled pouch ZIBs displayed a stable capacity (retention: 80%) after 50 self-charging cycles. They can be charged at various modes, such as galvanostatic or/and self-charging in dark or light, demonstrating a powerful ability to harvest and store energy in different external environments. This work provides a facile and effective route to optimize performance for the practical applications of self-charging ZIBs in self-powered systems, clean energy harvest/storage, city power supply, etc.