Solar Cells Research Articles

The origins of nonlinear peculiarities on the IV characteristics of multi-junction solar cells

The paper presents an overview of studies of the multi-junction (MJ) solar cells (SC) with IV characteristics having nonlinear peculiarities. It is shown that such peculiarities can arise either due to hetero-interface barriers (HB) for majority charge carriers or due to problems with tunnel diodes (TD). It is usually difficult to identify which of these hetero-structural objects is the cause of this nonlinearity, since the peculiarities appear similarly in the IV characteristics of MJ SC. The experimental method presented in this work is based on the study of IV characteristics during the overheating of MJ SCs. The behavior of nonlinear peculiarities caused by an imperfect TD or an HB is fundamentally different during the overheating of SCs, which makes it possible to identify the type of hetero-structural object. Since the number of hetero-interfaces in MJ SC is large, a method determining the position of problematic objects in the MJ structure was also developed. The method is based on the illumination of individual subcells using different laser wavelengths. Both methods considered were tested experimentally on GaInP/GaAs/Ge SCs.

Recrystallizing Sputtered NiOx for Improved Hole Extraction in Perovskite/Silicon Tandem Solar Cells

AbstractSputtering nickel oxide (NiOx) is a production‐line‐compatible route for depositing hole transport layers (HTL) in perovskite/silicon tandem solar cells. However, this technique often results in films with low crystallinity and structural flaws, which can impair electronic conductivity. Additionally, the complex surface chemistry and inadequate Ni3+/Ni2+ ratio impede the effective binding of self‐assembled monolayers (SAMs), affecting hole extraction at the perovskite/HTL interface. Herein, these issues are addressed using a recrystallization strategy by treating sputtered NiOx thin films with sodium periodate (NaIO4), an industrially available oxidant. This treatment improved crystallinity and increased the Ni3+/Ni2+ ratio, resulting in a higher content of nickel oxyhydroxide. These enhancements strengthened the SAM's anchoring capability on NiOx and improved the hole extraction at the perovskite/HTL interface. Moreover, the NaIO4 treatment facilitated Na+ diffusion within the perovskite layer and minimized phase separation, thus improving device stability. As a result, single‐junction perovskite solar cells with a 1.68 eV bandgap achieve a power conversion efficiency (PCE) of 23.22% for an area of 0.12 cm2. Perovskite/silicon tandem cells with an area of 1 cm2 reached a PCE of 30.48%. Encapsulated tandem devices retained 95% of their initial PCE after 300 h of maximum power point tracking under 1‐sun illumination at 25 °C.

Characterization and Performance Evaluation of Ni-Doped SnO2 Thin Films for Optoelectronic Applications: Structural, Optical, and Electrical Insights

Abstract Undoped and Ni-doped tin oxide thin films were synthesized using the spray pyrolysis technique on ordinary glass substrates. The study aimed to investigate the physico-chemical properties of these thin films using various characterization techniques. X-ray diffraction analysis revealed a polycrystalline behavior with a tetragonal structure and a preferential orientation along the direction for both undoped and Ni-doped SnO2 films. Raman spectroscopy confirm the tetragonal rutile structure and shows a slight enhancement of crystallinity for 4% Ni doped SnO2 thin films. Optical measurements showed a decrease in transmittance with increasing dopant ratio, indicating reduced transparency, and a decrease in band gap with Ni insertion. Electrical measurements, conducted through I-V curve analysis, confirmed Ohm's law compliance and indicated a decrease in resistivity with Ni doping, suggesting improved electrical conductivity. Additionally, the study explored the performance of thin-film solar cells utilizing SnO2 as a transparent conducting layer through numerical simulations using SCAPS-1D software. The effects of Ni doping on the solar cell performance were examined, suggesting potential enhancements or modifications in efficiency and functionality. Overall, the findings provide valuable insights into the structural, optical, and electrical properties of undoped and Ni-doped SnO2 thin films, offering promising avenues for their application in optoelectronic devices.

Aluminum-Doped Indium Oxide Electron Transport Layer Grown by Atomic Layer Deposition: Highly Efficient and Damage-Resistant Interconnection Solution for All-Perovskite Tandem Solar Cells with 25.46% Efficiency.

In fabricating high-efficiency all-perovskite tandem solar cells (APTSCs) with a p-i-n configuration, the electron transport layer (ETL) plays a critical role in facilitating the transport of photogenerated electrons from the front cell to the recombination layer and protecting the front cell from damage during rear cell fabrication. This study introduces aluminum-doped In2O3 (AIO) films grown by atomic layer deposition (ALD) as a promising ETL for high-efficiency APTSCs. ALD-grown AIO films with an optimized Al concentration exhibit superior charge transport characteristics, excellent transparency, and damage-resistant barrier properties against solution infiltration compared with conventional SnO2 ETLs and undoped ALD In2O3. Using an ALD SnO2/3 at.% AIO bilayer as the electron transport layer, an efficiency of 18.33% is achieved from single-junction wide bandgap perovskite solar cells. Furthermore, the use of ALD SnO2/3 at.% AIO ETL enables the reliable fabrication of APTSCs with negligible solution damage to the front cell and minimized power loss. Consequently, APTSC employing the ALD AIO-based ETL exhibit an excellent photoconversion efficiency of 25.46%, outperforming APTSCs with the ALD SnO2 ETL.

Overcoming the Tradeoff of Visible Transparency and Electrical Conductance via Dual Smoothing of Dielectric/Metal Interfaces in Cu-Thin-Layer-Based Transparent Electrodes.

The rapid advancement of flexible optoelectronic devices, such as light-emitting diodes, solar cells, and electrochromic devices, necessitates the development of high-performance flexible transparent electrodes (TEs). Dielectric/metal/dielectric (DMD)-type TEs are promising alternatives to conventional indium tin oxide (ITO) due to the high electrical conductance, excellent visible transparency, and sufficient mechanical flexibility. However, the tradeoff between electrical conductance and visible transparency poses a challenge to performance enhancement. This study introduces an Ar-ion-mediated interface modification method to address this tradeoff by dual smoothing of dielectric/metal interfaces in TiOx/Cu/ZnO TEs. Implementing this dual smoothing methodology significantly enhances both electrical conductance and visible light transmittance, achieving a Haacke figure of merit 200% higher than that of an unmodified otherwise identical structure. The highest figure of merit is 0.113 Ω-1, a record high for Cu-thin-layer-based DMD TEs, far surpassing ITO electrode values. Further, the enhanced optoelectronic performance remains highly durable under severe and simultaneous electrical, thermal, and mechanical stresses, showcasing the potential for significant advances in flexible optoelectronics.

Designing a Highly Crystalline Polymer Donor with Alkylsilyl and Fluorine Substitution to Achieve Efficient Ternary Organic Solar Cells.

Adopting a ternary strategy is an effective approach to enhance the power conversion efficiency (PCE) in organic solar cells (OSCs). Previous research on highly efficient ternary systems has predominantly focused on those based on highly crystalline dual small molecule acceptors. However, limited attention has been given to ternary systems utilizing dual polymer donors. Herein, by incorporating the fluorine and alkylsilyl substitution, a new polymer donor named PX1 is developed, which demonstrates strong crystallinity and excellent miscibility with polymer PM6. Moreover, PX1 broadens and enhances the absorption properties of the PM6:L8-BO blends, and its molecular orbital energy level is situated between those of PM6 and L8-BO, highlighting its suitability as a third component. Introducing 20% PX1 into the PM6:L8-BO system resulted in a high PCE of 18.82%. PX1 effectively suppresses charge recombination and reduces energy losses, while also serving as a morphology modulator that enhances the crystallization and improves the molecular packing order of the active layer by shortening the π-π stacking distance and extending crystalline coherence length. These factors collectively contribute to the performance improvements in ternary devices. This study demonstrates that employing a dual polymer donor strategy is a promising approach for achieving high-performance ternary OSCs.

High-efficiently stable cellulose triacetate modified perovskite solar cells

High-efficiently stable cellulose triacetate modified perovskite solar cells

Across‐Interface Effect of Alkylamine Salt on the Formation of Intermediate Phase and Defect Passivation in High‐Performance of Perovskite Solar Cells

AbstractHigh‐quality and low‐defect perovskite active layer (PVK) and electron transport layer (ETL) are essential for high‐performance perovskite solar cells (PSCs). Herein, an alkylamine salt, cyclohexylmethylammonium chloride (CMACl) is introduced into tin oxide (SnO2) ETL. CMACl, possessing protonated −NH3+ group and Cl− ions, not only effectively inhibits the aggregation of SnO2 colloids and enhances the quality of the ETLs, but also reduces and passivates the defects on ETLs. On the other hand, via the across‐interface effect of alkylamine salt by thermal diffusion, the CMACl‐PbI2 intermediate phase is formed and leads to the high quality of PVK, meanwhile, the defect on the buried interfaces and in the bulk of PVK are passivated by CMA+ and Cl− ions. Consequently, the CMACl‐modified PSC achieves a preeminent power conversion efficiency of 25.47% and excellent stability. This work demonstrates a facile and effective approach for synchronous optimization of ETL and PVK for high‐performance PSCs by across‐interface effect.

Fabrication of heterostructure multilayer devices through the optimization of Bi-metal sulfides for high-performance quantum dot-sensitized solar cells.

In this work, a titanium dioxide and lead sulfide (TiO2/PbS) nano-size heterostructure with tin sulfide was fabricated and coated via a two-step direct deposition process. Its microstructure, morphology, elemental composition, optical absorption, and photochemical activity were investigated. Linear sweep voltammetry and cyclic voltammetry curves substantiated its catalytic activity, indicating quantum dot effects of a well-developed space charge domain on the surface of the hybrid structure. These give rise to electron-hole recombination suppression and a high charge mobility rate. Moreover, direct stabilization was identified in current density, corresponding to the hybrid structures limiting the diffusion current process. Higher J SC values observed were substantiated by the role of quantum dot-size effects and enhanced crystalline structures, leading to a reduction in series resistance and an improved conversion efficiency of 10.05%. Overall, theoretical analyses and empirical findings indicated that the seamless migration of photoexcited electrons across the interfaces of SnS and PbS is linked to quantum dot effect synergy. This is facilitated by the space charge region, which serves as a conduit for efficient electron transfer between the respective materials.

Investigation of Internal Thermal Distribution in Inverted Perovskite Solar Cell and Improvement of its Heat Dissipation Performance

Abstract COMSOL Multiphysics software was used to construct a numerical opto-electro-thermal coupling model to investigate the mechanisms of internal heat generation, conduction, and dissipation in inverted (p-i-n architecture) perovskite solar cells (PSCs). The research results indicate that Joule heating and Shockley-Read-Hall (SRH) recombination are the primary sources of heat, leading to significant accumulation of heat at the interfaces between the perovskite and the electron transport layer (ETL), as well as between the ETL and the electrode. This concentration of heat not only affects the performance of the device but also poses challenges for overall thermal management. Therefore, we compared four different top electrode materials (Ag, Cu, Al, and reduced graphene oxide) to assess their performance in terms of heat dissipation efficiency. The results showed that reduced graphene oxide (RGO) performed exceptionally well in heat dissipation efficiency, primarily due to its high thermal conductivity, which enables it to effectively reduce heat accumulation at the interfaces, thereby improving performance of PSCs. This finding provides important material selection criteria for optimizing the thermal management of PSCs.

Overcoming the Open-Circuit Voltage Losses in Narrow Bandgap Perovskites for All-Perovskite Tandem Solar Cells

Overcoming the Open-Circuit Voltage Losses in Narrow Bandgap Perovskites for All-Perovskite Tandem Solar Cells

Template-Assisted Growth of High-Quality α-Phase FAPbI3 Crystals in Perovskite Solar Cells Using Thiol-Functionalized MoS2 Nanosheets.

Formamidinium lead iodide (FAPI) has gained attention for hybrid perovskite solar cell (PSC) applications due to its enhanced stability and narrow bandgap. However, a significant challenge remains in inducing and stabilizing the elusive perovskite "black phase"─photoactive cubic α-FAPI─as the relatively bulky FA+ cations tend to favor the thermodynamically stable nonphotoactive "yellow phase". In this study, we present a templated growth strategy employing thiol-functionalized MoS2 nanosheets as templates. By introduction of 3-mercaptopropionic acid (MPA)-functionalized MoS2 as a growth template, precise control over crystal formation was achieved, favoring the growth of high-quality α-FAPI films. These advanced templated films exhibited substantial improvements in charge transport properties, efficient light absorption, and enhanced charge extraction. As a result, the PSCs achieved a significantly enhanced power conversion efficiency (PCE) compared to the nontemplated control device, increasing from 20.6 to 22.5%. The MoS2-incorporated device also demonstrated excellent shelf stability, maintaining 91% of the initial PCE even after 1600 h of storage without device encapsulation.

Tailored Polymer Hole-Transporting Materials with Multisite Passivation Functions for Effective Buried-Interface Engineering of Inverted Quasi-2D Perovskite Solar Cells.

Although quasi-2D Ruddlesden‒Popper (RP) perovskite exhibits advantages in stability, their photovoltaic performance are still inferior to 3D counterparts. Optimizing the buried interface of RP perovskite and suppress energetic losses can be a promising approach for enhancing efficiency and stability of inverted quasi-2D RP perovskite solar cells (PSCs). Among which, constructing polymer hole-transporting materials (HTMs) with defect passivation functions is of great significance for buried-interface engineering of inverted quasi-2D RP PSCs. Herein, by employing side-chain tailoring strategy to extend the π-conjugation and regulate functionality of side-chain groups, target polymer HTMs (PVCz-ThSMeTPA and PVCz-ThOMeTPA) with high mobility and multisite passivation functions are achieved. The presence of more sulfur atom-containing groups in side-chain endows PVCz-ThSMeTPA with increased intra/intermolecular interaction, appropriate energy level, and enhanced buried interfacial interactions with quasi-2D RP perovskite. The hole mobility of PVCz-ThSMeTPA is up to 9.20×10-4 cm2 V-1 S-1. Furthermore, PVCz-ThSMeTPA as multifunctional polymer HTM with multiple chemical anchor sites for buried-interface engineering of quasi-2D PSCs can enable effective charge extraction, defects passivation, and perovskite crystallization modulation. Eventually, the PVCz-ThSMeTPA-based inverted quasi-2D PSC achieves a champion power conversion efficiency of 22.37%, which represents one of the highest power conversion efficiencies reported to date for quasi-2D RP PSCs.

SCAPS numerical modeling of novel CBTS/WO₃ thin film solar cell

SCAPS numerical modeling of novel CBTS/WO₃ thin film solar cell

Dual efficacy of potassium-doping in perovskite solar cells: Reducing hysteresis and boosting open-circuit voltage

The incorporation of potassium into perovskite solar cells (PSCs) has been empirically validated to mitigate hysteresis phenomena and boost the power conversion efficiency (PCE). However, the doping mechanism of potassium ions in the perovskite film and their effect on photocarrier recombination remains a topic of debate. Here, we grew doped MAPbI3: K single crystals by inverse temperature crystallization using KI as a dopant, and then perovskite thin films were spin-coated with dissolved MAPbI3: K crystals as a precursor. The doped MAPbI3: K perovskite films exhibit better crystal quality with large columnar grains and lower defect density. Employing Hall effect, ultraviolet photoelectron spectroscopy, and Kelvin probe force microscopy measurements, we definitively demonstrate that K-doping transforms the conductivity type of the perovskite film from a marginally N-type to a distinct P-type semiconductor. Furthermore, this doping strategy induces a concurrent downward shift in both the conduction band minimum and valence band maximum. As a result, the PCE of the PSCs increases from 15.15% to an impressive 20.66%, and the J–V curve hysteresis almost disappears. Additionally, theoretical simulations using SCAPS-1D software reveal a profound modification in the device's energy band diagram after K+-doping. Specifically, the energy level offset between the perovskite layer and the electron transport layer diminishes from 0.24 to 0.14 eV, with a result of bigger quasi-Fermi energy level splitting. This, in turn, elevates the open-circuit voltage (Voc) of the doped perovskite solar cell, underscoring the profound impact of potassium doping on enhancing PSC performance.

Efficient and stable inverted perovskite solar cells enabled by homogenized PCBM with enhanced electron transport

Fullerene derivatives are extensively employed in inverted perovskite solar cells due to their excellent electron extraction capabilities. However, [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) agglomerates easily in solution and exhibits a relatively low ionization barrier, increasing charge recombination losses and charge accumulation in the interface. Here, tetramethylthiuram disulfide (TMDS) is introduced into the PCBM solution to induce the formation of reducing sulfur radicals through UV light irradiation, allowing for n doping of the PCBM material. The resulting modified PCBM layer exhibits enhanced conductivity and electron mobility, significantly suppressing charge recombination. As a result, the resulting devices incorporating TMDS achieve a champion efficiency of 26.10% (certified 25.39%) and 24.06% at a larger area (1.0 cm2) with negligible hysteresis. More importantly, the optimized devices retain 95% and 90% of their initial efficiency after 1090 h under damp heat testing (85 °C and 85% relative humidity) and after 1271 h under maximum power point-tracking conditions, respectively.

The impact of charge carrier dynamics on the outdoor performance of cesium-lead-halide perovskite photovoltaics

We investigated the optoelectronic characteristics of cesium-based perovskite using various techniques. The steady-state photoluminescence (PL) spectroscopy of this perovskite solar cell composition shows the presence of strong peaks at a wavelength of 759 nm, which that corresponds to a band gap energy 1.63 eV. This band gap energy was estimated using two complementary methods, the PL emission spectra and the UV–vis absorption spectra. The study describes the dependence of photon energy on wavelength using a Gaussian mathematical model. Real-outdoor performance testing was conducted in Ethiopia’s climate during the hottest seasons to study the device performance under outdoor conditions at varying irradiances. Moreover, we investigated power generation from the devices using current–time measurements and analyzed charge carrier dynamics through transient photocurrent measurements.

On a drift‐diffusion model for perovskite solar cells

AbstractWe introduce a vacancy‐assisted charge transport model for perovskite solar cells. This instationary drift‐diffusion system describes the motion of electrons, holes, and ionic vacancies and takes into account Fermi–Dirac statistics for electrons and holes and the Fermi–Dirac integral of order for the mobile ionic vacancies in the perovskite. The free energy functional we work with corresponds to that choice of the statistical relations. To verify the existence of weak solutions, we consider a problem with regularized state equations and reaction terms on any arbitrarily chosen finite time interval. We motivate its solvability by time discretization and passage to the time‐continuous limit. A priori estimates for the chemical potentials that are independent of the regularization level ensure the existence of solutions to the original problem. These types of estimates rely on Moser iteration techniques and can also be obtained for solutions to the original problem.

Comprehensive evaluation of mechanical properties, optoelectronic features, photovoltaic performance, and crystal stability of Ba3MX3 (M = As, Sb; X = Cl, Br, I)

Herein, the first-principles computations are utilized to study the optoelectronic properties, photovoltaic performance, crystal stability, and mechanical features of Ba3MX3 (M = As, Sb; X = Cl, Br, I). Through comprehensive structural stability evaluation, all compounds are determined to be stable. The results indicate that Ba3MX3 (M = As, Sb; X = Cl, Br) is brittle while both Ba3AsI3 and Ba3SbI3 are ductile. The HSE06-based electronic structure calculations show that the direct-gap nature is revealed for six compounds, and the energy band gaps are within the range of 1.35–1.65 eV. The fundamental band gap can be modulated by virtue of X-anion substitution. The low carrier effective masses are disclosed for these compounds. Their optical features exhibit that high solar absorption and weak reflectance and energy loss are observed. Ultimately, an ultra-high theoretical conversion efficiency of 31.9 % is implemented for Ba3MI3 (M = As, Sb). Besides, the remaining four compounds also have high conversion efficiencies within 29–30 %. From the suitability for practical applications, both Ba3AsI3 and Ba3SbI3 are chosen as the best candidates for the absorber layers of effective single-junction solar cells. Our findings unveil the suitability of these inorganic materials for optoelectronic applications.

Sub-nA photovoltaic energy harvesting circuit for miniaturized battery-less sensor edges

Abstract In this letter, we report on the photovoltaic energy harvesting circuit for miniaturized, battery-less sensor devices. To accumulate nanowatt power from ultra-small photovoltaic cells, it is essential to reduce the minimum operating current of the energy harvesting circuit. To reduce the minimum operating current, we propose a dual-capacitance voltage monitor (DCVM) which can overcome the issue of the voltage drop caused by the shoot-through current for switching. We designed the energy harvesting circuit including the DCVM in a 180nm CMOS standard process, and successfully demonstrate the minimum operating current of 1 nA.