Single-junction Devices Research Articles

Semi-Monolithic Multijunction Devices for Unassisted Photoelectrochemical Water Splitting

Although foundational to multi-junction (MJ) photoelectrochemical (PEC) device synthesis, monolithic integration presents major limitations in process compatibility. Consequently, conductive adhesive-based interconnection scheme emerged as a suitable method to overcome limitations and to integrate incompatible material classes into MJ devices without compromising the integrity of the constituent layers. As the conductive adhesive generally employ a polymer matrix, the conductivity of this composite material depends on the conductive filler material. Among which, a core-shell type silver coated PMMA (Ag-PMMA) conductive microsphere filler has gained significant interest in the PV and PEC community due to its ability to exhibit reliable out-of-plane electrical conductivity (0.1 Ω-cm2) and good optical transparency (T > 90%), as we demonstrate for an epoxy-based transparent conductive composite (TCC) consisting of low particle loading (0.1 - 5 vol%).By implementation of the Ag-PMMA based TCC paired with a device exfoliation method, further referred to as semi-monolithic integration, independently processed substrate-grown single junction (SJ) devices were successively bonded and transferred via exfoliation onto a single host substrate to create a MJ device. As a proof-of-concept demonstration, we constructed the world’s first whole-chalcopyrite triple junction MJ device comprising 1.13 eV and 1.44 eV Cu(In,Ga)Se2 and 1.85 eV CuGa3Se5 sub-cells, with the TCC acting as the recombination layer between each sub-cell. The device exhibited an open circuit voltage of 1.85 V and is capable of splitting water with an STH efficiency of 3% in a PV-electrolysis configuration. Furthermore, a TCC-based bifacial MJ device comprising 1.7eV perovskite and 1.1eV Cu(In,Ga)Se2 sub-cells exhibited STH efficiency exceeding 10% in a PV-electrolysis configuration.Although the use of Ag-PMMA based TCC has shown to be an effective approach to prepare MJ devices, mechanical and electrical design and optimization is required to reliably appropriate the TCC as an optoelectronic device interconnect and to scale the semi-monolithic integration method. In the context of mechanical optimization, it has been shown that the degree of deformation of conductive microsphere filler is a key factor in establishing electrical connections. Up until now, the load-deformation characteristic of a single Ag-PMMA microsphere has not been measured. As such, we present in this communication a mechanical model based on measured load-deformation characteristics of a single Ag-PMMA microsphere to facilitate a spring model to better predict the deformation of multi-particle systems with respect to applied load. Furthermore, a finite element electrical model is implemented to determine the effects of electrical contacts across the sub-cell emitter layer and the resulting charge transport resistive losses. Hence, we demonstrate the critical factors influencing the quality of TCC as an anisotropic electrical interconnection layer, and provide a computational mechanical and electrical model to understand and mitigate parasitic resistive losses.

Performance optimization of MA0.5FA0.5PbI3/CsPbI3 based hybrid perovskite solar cell emphasizing on double absorber layer

Abstract The utilization of cesium-based lead halide (CsPbI3) PSC has considerable potential in the photovoltaic industry due to their high efficiency, underpinned by features such as a high absorption coefficient, thermal stability, and commendable efficiency. Nevertheless, the bandgap of CsPbI3, standing at 1.7 eV, poses a challenge as it is relatively high for a single-junction device. To overcome this limitation, we introduced a dual absorber layer structure by interleaving CsPbI3 with a lead-based hybrid perovskite material, denoted as MA0.5FA0.5PbI3. This investigation focused on the MA0.5FA0.5PbI3/CsPbI3 hetero-junction structure to ascertain the maximum possible efficiency. Therefore, this study proposed a PSC with the configuration of Ag/MoO3/MA0.5FA0.5PbI3/CsPbI3/IGZO/Au. In this setup, MoO3 (Molybdenum Trioxide) is used as the HTL and IGZO (Indium Gallium Zinc Oxide) as the ETL. Silver (Ag) serves as the back contact and gold (Au) is the front contact. This device demonstrated remarkable characteristics with Voc = 1.307 V, Jsc = 22.71 mA cm−2, FF = 86.58%, and η = 26.21%, showcasing a substantial improvement compared to previously reported CsPbI3-based homojunction PSCs. Furthermore, this study delved into the effects of absorber doping, absorber material thickness, bulk defect, and interfacial defects on solar cell parameters to obtain high-performance solar cells.

Chalcogenide perovskites for solar energy applications: The role of Sn substitution in BaZrS3-based photovoltaic devices

This study investigates the photovoltaic potential of the chalcogenide perovskite BaZr1-xSnxS3, where x values of 0, 0.125, and 0.250 were chosen. The band gap of BaZrS3 (1.7 eV) is slightly larger than the optimal band gap for single-junction devices, and alloying with Sn has been explored to tune the band gap. The photovoltaic performance of devices with different absorber layers was simulated using the SCAPS-1D solar cell simulator software. The results show that the power conversion efficiency (PCE) increases with increasing Sn content, and the optimal PCE is achieved at x = 0.125. The effects of temperature, work function of the back contact, and band offset at the ETL/absorber and absorber/HTL interfaces on the device performance were also investigated. The results show that the PCE decreases with increasing temperature, and the optimal PCE is achieved at a back contact work function of 4.8 eV. The study shows that tailoring band offset at the ETL/absorber and absorber/HTL interfaces can lead to efficiencies about 20 %, highlighting BaZr1-xSnxS3 as a promising material for future high-efficiency solar photovoltaics.

Optimization of the Active Layer Thickness for Inverted Ternary Organic Solar Cells Achieves 20% Efficiency with Simulation

Energy harvesting from cleaner sources and preserving the environment from dangerous gasses are presently the key priorities globally to maintain sustainable development. In this context, photovoltaic technology plays a vital role in generating energy from ternary organic solar cells. Ternary organic solar cells display significant potential for achieving outstanding photovoltaic performance compared to binary structures. Over the past few years, significant endeavors to develop novel organic materials have led to a consistent rise in efficiency, surpassing 19% for single-junction devices. In our study, we simulated an inverted ternary organic solar cell (TOSC) structure employing the one-dimensional optical and drift diffusion model and using “Oghma-Nano 8.0.034” software by optimizing the active blend thickness at 80 nm within the structure of ITO/SnO2/PM6:D18:L8-BO/PEDOT:PSS/Ag. We simulated different performance parameters such as EQE, Photo-CELIV, PCE, Jsc, Voc, and FF with different active layer thicknesses ranging from 50 to 200 nm to discover the behavior of the device in terms of efficiency parameters. Furthermore, the structure attained a PCE of 20% for an active layer thickness of 80 nm within a Jsc of 27.2 mA cm−2, a Voc of 0.89 V, and an FF of 82.3%. This approach can potentially be valuable in constructing a highly effective TOSC model in the laboratory.

A High-Performance Organic Photovoltaic System with Versatile Solution Processability.

Recently developed organic photovoltaic (OPV) materials have simultaneously closed the gaps in efficiency, stability, and cost for single-junction devices. Nonetheless, the developed OPV materials still pose big challenges in meeting the requirements for practical applications, especially regarding the prevalent issues of solution processability. Herein, a highly efficient polymer donor, named DP3, incorporating an electron-rich benzo[1,2-b:4,5-b']dithiophene unit as well as two similar and simple acceptor units is presented. Its primary objective is to enhance the interchain and/or intrachain interactions and ultimately fine-tune bulk-heterojunction microstructure. The DP3:L8-BO system demonstrates the highest power conversion efficiency (PCE) of 19.12%. This system also exhibits high-performance devices with over 18% efficiencies for five batches with various molecular weights (23.6-80.8KDa), six different blend thicknesses (95-308nm), differenced coating speeds (3.0-29.1mmin-1), with promising PCEs of 18.65% and 15.53% for toluene-processed small-area (0.029cm2) cells and large-area (15.40cm2) modules, thereby demonstrating versatile solution processability of the designed DP3:L8-BO system that is a strong candidate for commercial applications.

Improving FAPbBr3 Perovskite Crystal Quality via Additive Engineering for High Voltage Solar Cell over 1.5 V.

Lead bromide-based perovskites are promising materials as the top cells of tandem solar cells and for application in various fields requiring high voltages owing to their wide band gaps and excellent environmental resistances. However, several factors, such as the formation of bulk and surface defects, impede the performances of corresponding devices, thereby limiting the efficiencies of these devices as single-junction devices. To reduce the number of defect sites, urea is added to the formamidinium lead bromide (FAPbBr3) perovskite material to increase its grain size. Nevertheless, urea undesirably reacts with lead(II) bromide (PbBr2) in the perovskite structure, creating unfavorable impurities in the device. To solve this problem, herein, in addition to urea, we introduced formamidinium chloride (FACl) into FAPbBr3. Owing to the synergistic effect of urea and FACl, the FAPbBr3 film quality effectively improved due to suppression of the generation of impurities and stabilization of film crystallinity. Consequently, the FAPbBr3 single-junction solar cell constructed using FACl and urea as additives demonstrated a power conversion efficiency of 9.6% and an open-circuit voltage of 1.516 V with negligible hysteresis. This study provides new insights into the use of additive engineering for overcoming the energy losses caused by defects in perovskite films.

Advances in Mixed Tin-Lead Narrow-Bandgap Perovskites for Single-Junction and All-Perovskite Tandem Solar Cells.

Organic-inorganic metal-halide perovskites have received great attention for photovoltaic (PV) applications owing to their superior optoelectronic properties and the unprecedented performance development. For single-junction PV devices, although lead (Pb)-based perovskite solar cells have achieved 26.1% efficiency, the mixed tin-lead (Sn-Pb) perovskites offer more ideal bandgap tuning capability to enable an even higher performance. The Sn-Pb perovskite (with a bandgap tuned to ≈1.2eV) is also attractive as the bottom subcell for a tandem configuration to further surpass the Shockley-Queisser radiative limit for the single-junction devices. The performance of the all-perovskite tandem solar cells has gained rapid development and achieved a certified efficiency up to 29.1%. In this article, the properties and recent development of state-of-the-art mixed Sn-Pb perovskites and their application in single-junction and all-perovskite tandem solar cells are reviewed. Recent advances in various approaches covering additives, solvents, interfaces, and perovskite growth are highlighted. The authors also provide the perspective and outlook on the challenges and strategies for further development of mixed Sn-Pb perovskites in both efficiency and stability for PV applications.

Low temperature method-based evaporation/spray-coating technology for wide bandgap perovskite solar cells

Years of working on perovskite solar cells (PSCs)-based tandem devices and single-junction devices have approved that low annealing temperatures can be beneficial for improving device performances. In this study, pseudo-halogen ion engineering works well in the evaporation/spray-coating method. According to our research, it is has been proven that the addition of formamidine acetate (FAAc) can effectively reduce the annealing temperature from 170 °C to 150 °C, accelerate the maturation process of the perovskite films, and broaden the annealing window. As a result, a perovskite film with homogeneous crystallization and low residual stress is achieved, leading to extended charge carrier lifetimes, elevated photoluminescence quantum yields (PLQY), reduced Urbach energies. The corresponding PSCs were prepared through evaporation/spray-coating method achieves an impressive power conversion efficiency (PCE) of 19.46%, which is the highest efficiency among wide-bandgap (WBG) PSCs fabricated by this method. And the unencapsulated devices exhibit satisfactory stability, retaining 80% of the initial PCE after 600 h of thermal aging at 60 °C and retaining 90% of the initial PCE after 1500 h of 50% humidity aging at 25 °C, respectively.

From Sunrise to Sunset: Unraveling Metastability in Perovskite Solar Cells by Coupled Outdoor Testing and Energy Yield Modelling

AbstractPerovskite‐based solar cells exhibit peculiar outdoor performance which is not yet fully understood. The results of outdoor tests may contain hidden, but valuable information that cannot be fully extracted from measurements alone. One such phenomenon is the effect of nighttime degradation and the subsequent light‐soaking recovery, which can take from a few hours in the morning up to the entire day. In this work, long‐term outdoor monitoring is combined with energy yield modeling to qualitatively and quantitatively investigate the effect of light‐soaking recovery in both single junction and tandem perovskite‐based devices. Following the novel methodology presented in this study, it is observed that the light‐soaking effect depends not only on the daily irradiation but also on the device temperature, and it can be described using a simple empirical formalism. Incorporating this dependency into the energy yield model results in an excellent agreement between the simulated and the measured outdoor data, which allows to perform long‐term prediction studies. The model estimates that the light‐soaking metastability effect decreases the attainable annual energy yield by up to ≈5% for the studied single junction devices, and for tandems by up to ≈3%, depending on the geographical location, and even more for non‐optimal device orientation.

19% efficiency in organic solar cells of Benzo[1,2-b:4,5-b′]Difuran-based donor polymer realized by volatile + non-volatile dual-solid-additive strategy

Though the application-promising photovoltaic technology named organic solar cells (OSCs) have been close to 20% benchmark power conversion efficiency (PCE) within fabrication friendly single-junction devices, these achievements are enabled by polymer donors based on benzodithiophene cores, requiring toxic production steps. Whilst, the bio-renewable benzo[1,2-b:4,5-b′]difuran unit constructed polymer donors cannot yield comparable efficiency, though their lower steric hindrance is widely appreciated. OSC field has paid great attention on optimizing their performance by chemistry design, yet the device engineering is relatively neglected compared to what have been done on the benzodithiophene side. Here we report a new dual additive strategy of simultaneously applying volatile (2-CN) and non-volatile (MF) solid additives to reduce non-radiative voltage loss and boost charge generation, via an occupying evaporated left vacancies in polymer matrix process. Consequently, the target system D18-Fu:L8-BO’s efficiency is promoted to 19.11%, representing the cutting-edge level of this research topic.

Narrow Bandgap Metal Halide Perovskites for All-Perovskite Tandem Photovoltaics.

All-perovskite tandem solar cells are attracting considerable interest in photovoltaics research, owing to their potential to surpass the theoretical efficiency limit of single-junction cells, in a cost-effective sustainable manner. Thanks to the bandgap-bowing effect, mixed tin-lead (Sn-Pb) perovskites possess a close to ideal narrow bandgap for constructing tandem cells, matched with wide-bandgap neat lead-based counterparts. The performance of all-perovskite tandems, however, has yet to reach its efficiency potential. One of the main obstacles that need to be overcome is the─oftentimes─low quality of the mixed Sn-Pb perovskite films, largely caused by the facile oxidation of Sn(II) to Sn(IV), as well as the difficult-to-control film crystallization dynamics. Additional detrimental imperfections are introduced in the perovskite thin film, particularly at its vulnerable surfaces, including the top and bottom interfaces as well as the grain boundaries. Due to these issues, the resultant device performance is distinctly far lower than their theoretically achievable maximum efficiency. Robust modifications and improvements to the surfaces of mixed Sn-Pb perovskite films are therefore critical for the advancement of the field. This Review describes the origins of imperfections in thin films and covers efforts made so far toward reaching a better understanding of mixed Sn-Pb perovskites, in particular with respect to surface modifications that improved the efficiency and stability of the narrow bandgap solar cells. In addition, we also outline the important issues of integrating the narrow bandgap subcells for achieving reliable and efficient all-perovskite double- and multi-junction tandems. Future work should focus on the characterization and visualization of the specific surface defects, as well as tracking their evolution under different external stimuli, guiding in turn the processing for efficient and stable single-junction and tandem solar cell devices.

A Deep Dive into Cu2ZnSnS4 (CZTS) Solar Cells: A Review of Exploring Roadblocks, Breakthroughs, and Shaping the Future.

Renewable energy is crucial for sustainable future, and Cu2ZnSnS4 (CZTS) based solar cells shine as a beacon of hope. CZTS, composed of abundant, low-cost, and non-toxic elements, shares similarities with Cu(In,Ga)Se2 (CIGS). However, despite its promise and appealing properties for solar cells, CZTS-based solar cells faces performance challenges owing to inherent issues with CZTS material, and conventional substrate structure complexities. This review critically examines these roadblocks, explores ongoing efforts and breakthroughs, providing insight into the evolving landscape of CZTS-based solar cells research. Furthermore, as an optimistic turn in the field, the review first highlights the crucial need to transition to a superstrate structure for CZTS-based single junction devices, and summarizes the substantial progress made in this direction. Subsequently, dive into the discussion about the fascinating realm of CZTS-based tandem devices, providing an overview of the existing literature as well as outlining the possible potential strategies for enhancing the efficiency of such devices. Finally, the review provides a useful outlook that outlines the priorities for future research and suggesting where efforts should concentrate to shape the future of CZTS-based solar cells.

Monolithic Selenium/Silicon Tandem Solar Cells

Selenium is experiencing renewed interest as a promising candidate for the wide bandgap photoabsorber in tandem solar cells. However, despite the potential of selenium-based tandems to surpass the theoretical efficiency limit of single-junction devices, such a device has never been demonstrated. In this study, we present the first monolithically integrated selenium/silicon tandem solar cell. Guided by device simulations, we investigate various carrier-selective contact materials and achieve encouraging results, including an open-circuit voltage of Voc=1.68V from suns-Voc measurements. The high open-circuit voltage positions selenium/silicon tandem solar cells as serious contenders to the industrially dominant single-junction technologies. Furthermore, we quantify a pseudo fill factor of more than 80% using injection-level-dependent open-circuit voltage measurements, indicating that a significant fraction of the photovoltaic losses can be attributed to parasitic series resistance. This work provides valuable insights into the key challenges that need to be addressed for realizing higher efficiency selenium/silicon tandem solar cells. Published by the American Physical Society 2024

Triple-junction solar cells with cyanate in ultrawide-bandgap perovskites.

Perovskite bandgap tuning without quality loss makes perovskites unique among solar absorbers, offering promising avenues for tandem solar cells1,2. However, minimizing the voltage loss when their bandgap is increased to above 1.90 eV for triple-junction tandem use is challenging3-5. Here we present a previously unknown pseudohalide, cyanate (OCN-), with a comparable effective ionic radius (1.97 Å) to bromide (1.95 Å) as a bromide substitute. Electron microscopy and X-ray scattering confirm OCN incorporation into the perovskite lattice. This contributes to notable lattice distortion, ranging from 90.5° to 96.6°, a uniform iodide-bromide distribution and consistent microstrain. Owing to these effects, OCN-based perovskite exhibits enhanced defect formation energy and substantially decreased non-radiative recombination. We achieved an inverted perovskite (1.93 eV) single-junction device with an open-circuit voltage (VOC) of 1.422 V, a VOC × FF (fill factor) product exceeding 80% of the Shockley-Queisser limit and stable performance under maximum power point tracking, culminating in a 27.62% efficiency (27.10% certified efficiency) perovskite-perovskite-silicon triple-junction solar cell with 1 cm2 aperture area.

A Universal Perovskite/C60 Interface Modification via Atomic Layer Deposited Aluminum Oxide for Perovskite Solar Cells and Perovskite-Silicon Tandems.

The primary performance limitation in inverted perovskite-based solar cells is the interface between the fullerene-based electron transport layers and the perovskite. Atomic layer deposited thin aluminum oxide (AlOX) interlayers that reduce nonradiative recombination at the perovskite/C60 interface are developed, resulting in >60 millivolts improvement in open-circuit voltage and 1% absolute improvement in power conversion efficiency. Surface-sensitive characterizations indicate the presence of a thin, conformally deposited AlOx layer, functioning as a passivating contact. These interlayers work universally using different lead-halide-based absorbers with different compositions where the 1.55 electron volts bandgap single junction devices reach >23% power conversion efficiency. A reduction of metallic Pb0 is found and the compact layer prevents in- and egress of volatile species, synergistically improving the stability. AlOX-modified wide-bandgap perovskite absorbers as a top cell in a monolithic perovskite-silicon tandem enable a certified power conversion efficiency of 29.9% and open-circuit voltages above 1.92 volts for 1.17 square centimeters device area.

Wavelength‐Recognizable SbSI:Sb2S3 Photovoltaic Devices: Elucidation of the Mechanism and Modulation of their Characteristics

AbstractThe output of photovoltaic (PV) devices is mostly independent of the wavelength of the incident light, whereas an anomalous wavelength‐dependent photovoltaic effect (WDPE) has recently been observed in antimony chalcohalide‐chalcogenide (SbSI:Sb2S3) PVs. Remarkably, the open‐circuit voltage (VOC) exhibits a reversible change between low VOC for short wavelengths and high VOC for long wavelengths. Herein, this work presents i) insights into the underlying mechanisms of this phenomenon by electron spin resonance (ESR) measurements and ii) the switchable character of WDPE depending on the hole transport material (HTM). Operando ESR measurements with light irradiation revealed that the hole density in the HTM is significantly suppressed when the ultraviolet component is included in the irradiation light. This indicated interfacial charge recombination rather than hole transfer to the HTM under short‐wavelength light irradiation, providing a basis for understanding the mechanism of WDPE. Furthermore, the use of poly(triarylamine) as the HTM unexpectedly exhibit the opposite wavelength‐VOC dependence, where a low VOC is observed with long‐wavelength light. In addition, the introduction of a polar gas accelerated the response speed of these effects. These findings shed light on the expansion of unique wavelength‐responsive single junction devices.

Multifunctional Effects of Biguanide Derivative in the Application of Highly Efficient Tin-Lead Perovskite Solar Cells.

Tin-lead (Sn-Pb) mixed perovskites is beneficial to a single-junction or all-perovskite tandem device. However, the poor quality of the perovskite surface resulting from Sn2+ oxidation and uncontrollable crystallization degrades device performance and stability. Herein, based on interface engineering, a novel biguanide derivative of PZBGACl is employed that integrates different types of N-related groups to reconstruct the surface/grain boundaries of Sn-Pb perovskite. Combined with the microcorrosion effect of isopropanol solvent, PZBGACl can induce surface recrystallization of perovskite, and passivate various types of defects via hydrogen bond or Lewis acid-base interaction, leading to an excellent perovskite film with reduced stress, larger grain size, and more n-type surface. As a result, the obtained Sn-Pb solar cell achieves a power conversion efficiency of 22.0%, and exhibits excellent N2 storage/operation stability.

Measurement and analysis of annual solar spectra at different installation angles in central Europe

The solar spectra in outdoor installations is very seldom equal to that under standard test conditions. This points to the importance of measuring, analyzing and understanding the implications of solar spectra variations with respect to the performance of solar cells. In this work, we present and analyze one year of sun spectra measured at two different angles in central Europe, where the spectrometers were installed at the optimum inclination angle and in vertical orientation, the latter being relevant for building integrated photovoltaics. We report for the first time the differences between the two inclination angles in terms of key performance indicators, such as average photon energy, blue fraction and spectral factor. Moreover, we show the impact of these spectral changes on the maximum current density of ideal single-junction and tandem devices in tilted and vertical orientations. Red-shifted solar spectra were more often found at the vertical installation in comparison to the optimum installation angle, which translated into up to 30% lower current-mismatch losses in idealized tandem devices throughout the year.

Transparent Recombination Electrode with Dual-Functional Transport and Protective Layer for Efficient and Stable Monolithic Perovskite/Organic Tandem Solar Cells.

Rational selection and design of recombination electrodes (RCEs) are crucial to enhancing the power conversion efficiency (PCE) and stability of monolithic tandem solar cells (TSCs). Sputtered indium tin oxide (ITO) with high conductivity and excellent transmittance is introduced as RCE in perovskite/organic TSCs. To prevent high-energy ITO particles destroy the underlying material during sputtering, dual-functional transport and protective layer (C1) is employed. The styryl group in C1 can be thermally crosslinked to serve as a sputtering protective layer. Meanwhile, the conjugated phenanthroline skeleton in C1 shows high electron mobility and hole blocking capability to promote the electron transport process at the interfaces and effectively reduce charge accumulation. Monolithic perovskite/organic TSC with high PCE of 24.07% and excellent stability is demonstrated by stacking a 1.77eV bandgap perovskite layer and a 1.35eV bandgap organic active layer. This strategy provides new insights for overcoming the fundamental efficiency limits of single-junction devices and promotes the further development of TSC devices.

Potentials of InxGa1-xN photovoltaic tandems

During the past few years a great variety of multi-junction solar cells has been developed with the aim of a further increase in efficiency beyond the limits of single junction devices. In this work, the solar power conversion efficiency of InxGa1-xN based tandem solar cells was investigated. With this intention, one simulation of the spectral response and the current-voltage characteristic was carried out using a simulation program designed under ‘Visual Basic 5’ language for this reason. Our cal culation indicates that the attainable efficiency can be enhanced up to 34 % and 37% for tandems with double and triple junctions respectively, obtained under 1-sun AM1.5 illumination and at ambient temperature, using realistic material parameters. A comparison has been made of our results with those of other models.