Certified Power Conversion Efficiency Research Articles

Shallow-level defect passivation by 6H perovskite polytype for highly efficient and stable perovskite solar cells

The power conversion efficiency of perovskite solar cells continues to increase. However, defects in perovskite materials are detrimental to their carrier dynamics and structural stability, ultimately limiting the photovoltaic characteristics and stability of perovskite solar cells. Herein, we report that 6H polytype perovskite effectively engineers defects at the interface with cubic polytype FAPbI3, which facilitates radiative recombination and improves the stability of the polycrystalline film. We particularly show the detrimental effects of shallow-level defect that originates from the formation of the most dominant iodide vacancy (VI+) in FAPbI3. Furthermore, additional surface passivation on top of the hetero-polytypic perovskite film results in an ultra-long carrier lifetime exceeding 18 μs, affords power conversion efficiencies of 24.13% for perovskite solar cells, 21.92% (certified power conversion efficiency: 21.44%) for a module, and long-term stability. The hetero-polytypic perovskite configuration may be considered as close to the ideal polycrystalline structure in terms of charge carrier dynamics and stability.

Solvent‐Assisted Surface Modification Using Metallocene‐Based Molecules for High‐Efficiency Perovskite/Silicon Tandem Solar Cells

AbstractThe presence of a high density of defects at the perovskite/electron transport layer (ETL) interface results in significant nonradiative recombination losses, thus impeding the efficiency enhancement of perovskite/silicon tandem solar cells (TSCs). In this investigation, a metallocene‐based molecule, cobalt (III) dichlorophene hexafluorophosphate (CcPF6), is employed for perovskite surface passivation. To maximize its efficacy, the molecule is dissolved in a mixed solvent of acetonitrile and chlorobenzene, leading to the reconstruction of the perovskite surface and effective passivation of surface defects. This modification strategy substantially enhances the overall efficiency of perovskite/silicon tandem solar cells by mitigating the issue of low fill factor resulting from non‐uniform coating of the top perovskite layer on the textured silicon bottom cell. Leveraging a double‐sided textured silicon heterojunction (HJT) bottom cell, a certified power conversion efficiency (PCE) of 30.43% for a monolithic perovskite/silicon TSC (1.00 cm2) is achieved, featuring an open‐circuit voltage (Voc) of 1.93 V and a fill factor (FF) of 78.43%. After storage in the drying cabinet (5% humidity at 20 °C) for 1000 h, the device retains 94.27% of its initial performance.

Stress-induced phase stability and optoelectronic property changes in cesium lead halide perovskites

Over the past decade, the certified power conversion efficiency of perovskite solar cells (PSCs) has increased to 26.1%. However, phase instability originating from lattice strains, has limited their commercialization. Strains will inevitably be generated during the PSC fabrication and service process due to the “soft lattice” nature of halide perovskites. In particular, flexible PSCs are subjected to not only mechanical tensile and compressive loads, but also suffer from thermal stresses. In this study, strain-induced changes in the phase stability and the corresponding optoelectronic properties of CsPbI3−xBrx (CsPbI3, CsPbBr3, and CsPbI2Br) systems under tensile and compressive stresses were investigated using first-principles calculations. The results showed that compressive stresses reduce the bandgap value and increase the light absorption coefficient; thus, the optoelectronic performance is improved, whereas the light absorption coefficient decreases regardless of how the bandgap changes under tensile stresses. Moreover, under the same stress, the tensile strain value was twice that of the compressive strain, and the critical value of the transition from the cubic to tetragonal phase was lower, indicating that phase stability was worse under tensile stresses. Therefore, during the fabrication of PSCs, the tensile stress state should be adjusted to the compressive stress state, which is favorable for enhancing PSCs photovoltaic performance and phase stability. The results not only provide direct evidence of tensile and compressive strains influencing the phase stability and optoelectronic property changes in halide perovskites, but also highlight lattice-strain tailoring for the composition design, process optimization, and interface engineering of efficient and stable PSCs.

Smart Materials to Empowering Perovskite Solar Cells with Self‐Healing Capability

Inspired by nature, intelligent self‐healing materials have recently been exploited also in the field of photovoltaics to mimic natural systems achieving self‐repairing. The past decade has witnessed perovskite solar cells (PSCs) skyrocketing to a certified power conversion efficiency of 26.1%. However, their intrinsic instability, when exposing to moisture, high temperature, and continuous illumination, hampers their commercial development for a long‐term use in ambient operating conditions. Therefore, the use of smart self‐healing materials, based on self‐assembling properties and dynamic interactions, empowers PSCs with self‐recovery abilities to reinforce their pivotal role as efficient photovoltaic devices and encourage their exploitation in the market. Herein, the current progress in self‐healing perovskite materials with a special focus on self‐recovery after moisture exposure or mechanical damage with the aim to provide a valuable insight for research on this topic to accelerate the PSC commercialization process is highlighted.

Unraveling the Molecular Size Effect on Surface Engineering of Perovskite Solar Cells.

Surface engineering in perovskite solar cells, especially for the upper surface of perovskite, is widely studied. However, most of these studies have primarily focused on the interaction between additive functional groups and perovskite point defects, neglecting the influence of other parts of additive molecules. Herein, additives with -NH3 + functional group are introduced at the perovskite surface to suppress surface defects. The chain lengths of these additives vary to conduct a detailed investigation into the impact of molecular size. The results indicate that the propane-1,3-diamine dihydroiodide (PDAI2 ), which possesses the most suitable size, exhibited obvious optimization effects. Whereas the molecules, methylenediamine dihydroiodide (MDAI2 ) and pentane-1,5-diamine dihydroiodide (PentDAI2 ) with unsuitable size, lead to a deterioration in device performance. The PDAI2 -treated devices achieved a certified power conversion efficiency (PCE) of 25.81% and the unencapsulated devices retained over 80% of their initial PCE after 600h AM1.5 illumination.

Homogeneous crystallization and buried interface passivation for perovskite tandem solar modules.

Scalable fabrication of all-perovskite tandem solar cells is challenging because the narrow-bandgap subcells made of mixed lead-tin (Pb-Sn) perovskite films suffer from nonuniform crystallization and inferior buried perovskite interfaces. We used a dopant from Good's list of biochemical buffers, aminoacetamide hydrochloride, to homogenize perovskite crystallization and used it to extend the processing window for blade-coating Pb-Sn perovskite films and to selectively passivate defects at the buried perovskite interface. The resulting all-perovskite tandem solar module exhibited a certified power conversion efficiency of 24.5% with an aperture area of 20.25 square centimeters.

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.

Oriented Molecular Bridge Constructs Homogeneous Buried Interface for Perovskite Solar Cells with Efficiency Over 25.3.

Buried interface optimization matters the efficiency improvement of planar perovskite solar cells (PSCs), and the molecular bridge is reported to be an effective approach. Herein, a molecular bridge is constructed at buried interface using 4-chloro-3-sulfamoylbenzoic acid (CSBA), and its preferred arrangement is systematically investigated. It is elucidated that the CSBA molecular is prone to be orientationally absorbed on TiO2 surface through COOH-Ti, and then connect with perovskite through S═O-Pb, resulting in a feasible oriented molecular bridge. Contributing to the passivated interfacial defects, optimized interfacial energy level, and released perovskite tensile stress, resulting from the oriented CSBA molecular bridge, the PSCs with an active area of 0.08 cm2 achieve a certified power conversion efficiency (PCE) of 25.32%, the highest among the TiO2-based planar PSCs. Encouragingly, the PSCs with an active area of 1 cm2 achieve a champion PCE of 24.20%, significantly promoting the efficiency progress of large-area PSCs. In addition, the PSCs with oriented CSBA molecular bridge possess enhanced stability, the unencapsulated PSCs can maintain ≈91% and ≈85% of their initial PCE after 3000 h aging under ambient condition and 1200 h aging under exposure to UV irradiation.

Sublimed C60 for efficient and repeatable perovskite-based solar cells

Thermally evaporated C60 is a near-ubiquitous electron transport layer in state-of-the-art p–i–n perovskite-based solar cells. As perovskite photovoltaic technologies are moving toward industrialization, batch-to-batch reproducibility of device performances becomes crucial. Here, we show that commercial as-received (99.75% pure) C60 source materials may coalesce during repeated thermal evaporation processes, jeopardizing such reproducibility. We find that the coalescence is due to oxygen present in the initial source powder and leads to the formation of deep states within the perovskite bandgap, resulting in a systematic decrease in solar cell performance. However, further purification (through sublimation) of the C60 to 99.95% before evaporation is found to hinder coalescence, with the associated solar cell performances being fully reproducible after repeated processing. We verify the universality of this behavior on perovskite/silicon tandem solar cells by demonstrating their open-circuit voltages and fill factors to remain at 1950 mV and 81% respectively, over eight repeated processes using the same sublimed C60 source material. Notably, one of these cells achieved a certified power conversion efficiency of 30.9%. These findings provide insights crucial for the advancement of perovskite photovoltaic technologies towards scaled production with high process yield.

Performance of Hydride Vapor Phase Epitaxy‐Grown GaInP Photovoltaics with Double‐Sided Al‐Containing Passivation Layers Under Air Mass 1.5 Global Solar Irradiation and Low‐Intensity Indoor Light Irradiation

High‐performance III–V photovoltaic devices have the potential for various applications; however, their high production cost represents a challenge for market expansion. Hydride vapor phase epitaxy (HVPE) is a fabrication technology that can reduce the epitaxial growth cost of III–V compound semiconductors. This study demonstrates the performances of HVPE‐grown GaInP photovoltaic devices for solar and indoor photovoltaic applications. Herein, HVPE‐grown GaInP photovoltaic devices with AlInP frontside and AlGaInP backside passivation layers are fabricated for the first time. The developed GaInP photovoltaic device measured under air mass 1.5 global solar spectrum illumination achieves an independently certified power conversion efficiency of 17.3%, which is a new record efficiency among HVPE‐grown GaInP single‐junction solar cells. Furthermore, the GaInP photovoltaic device grown using HVPE exhibits a high power conversion efficiency (34.7–37.1%) under an illumination of 500–2000 lux, respectively, emitted by a white light‐emitting diode. These results demonstrate that HVPE‐grown GaInP photovoltaic devices can be used in low‐intensity indoor light energy harvesting systems.

Toward the Commercialization of Perovskite Solar Modules.

Perovskite (PVSK) photovoltaic (PV) devices are undergoing rapid development and have reached a certified power conversion efficiency (PCE) of 26.1% at the cell level. Tremendous efforts in material and device engineering have also increased moisture, heat, and light-related stability. Moreover, the solution-process nature makes the fabrication process of perovskite photovoltaic devices feasible and compatible with some mature high-volume manufacturing techniques. All these features render perovskite solar modules (PSMs) suitable for terawatt-scale energy production with a low levelized cost of electricity (LCOE). In this review, the current status of perovskite solar cells (PSCs) and modules and their potential applications are first introduced. Then critical challenges are identified in their commercialization and propose the corresponding solutions, including developing strategies to realize high-quality films over a large area to further improve power conversion efficiency and stability to meet the commercial demands. Finally, some potential development directions and issues requiring attention in the future, mainly focusing on further dealing with toxicity and recycling of the whole device, and the attainment of highly efficient perovskite-based tandem modules, which can reduce the environmental impact and accelerate the LCOE reduction are put forwarded.

Multifunctional ytterbium oxide buffer for perovskite solar cells.

Perovskite solar cells (PSCs) comprise a solid perovskite absorber sandwiched between several layers of different charge-selective materials, ensuring unidirectional current flow and high voltage output of the devices1,2. A 'buffer material' between the electron-selective layer and the metal electrode in p-type/intrinsic/n-type (p-i-n) PSCs (also known as inverted PSCs) enables electrons to flow from the electron-selective layer to the electrode3-5. Furthermore, it acts as a barrier inhibiting the inter-diffusion of harmful species into or degradation products out of the perovskite absorber6-8. Thus far, evaporable organic molecules9,10 and atomic-layer-deposited metal oxides11,12 have been successful, but each has specific imperfections. Here we report a chemically stable and multifunctional buffer material, ytterbium oxide (YbOx), for p-i-n PSCs by scalable thermal evaporation deposition. We used this YbOx buffer in the p-i-n PSCs with a narrow-bandgap perovskite absorber, yielding a certified power conversion efficiency of more than 25%. We also demonstrate the broad applicability of YbOx in enabling highly efficient PSCs from various types of perovskite absorber layer, delivering state-of-the-art efficiencies of 20.1% for the wide-bandgap perovskite absorber and 22.1% for the mid-bandgap perovskite absorber, respectively. Moreover, when subjected to ISOS-L-3 accelerated ageing, encapsulated devices with YbOx exhibit markedly enhanced device stability.

Nanoscale spatial and time-resolved mapping in perovskite and organic solar cells: a multimodal technique to visualize the photoinduced charge dynamics

This perspective delves into the nanoscale photodynamics mapping of perovskite (PSCs) and organic solar cells (OSCs) using a multimodal approach to enhance photovoltaic performance.

Indoor Photovoltaic Fiber with an Efficiency of 25.53% under 1500 Lux Illumination.

Photovoltaic devices represent an efficient electricity generation mode. Integrating them into textiles offers exciting opportunities for smart electronic textiles-with the ultimate goal of supplying power for wearable technology-which is poised to change how electronic devices are designed. Many human activities occur indoors, so realizing indoor photovoltaic fibers (IPVFs) that can be woven into textiles to power wearables is critical, although currently unavailable. Here, a dye-sensitized IPVF is constructed by incorporating titanium dioxide nanoparticles into aligned nanotubes to produce close contact and stable interfaces among active layers on a curved fiber substrate, thus presenting efficient charge transport and low charge recombination in the photoanode. With the combination of highly conductive core-sheath Ti/carbon nanotube fiber as a counter electrode, the IPVF shows a certified power conversion efficiency of 25.53% under 1500lux illuminance. Its performance variation is below 5% after bending, twisting, or pressing for 1000 cycles. These IPVFs arefurther integrated with fiber batteries as self-charging power textiles, which aredemonstrated to effectively supply electricity for wearables, solving the power supply problem in this important direction.

Trace Water in Lead Iodide Affecting Perovskite Crystal Nucleation Limits the Performance of Perovskite Solar Cells.

The experimental replicability of highly efficient perovskite solar cells (PSCs) is a persistent challenge faced by laboratories worldwide. Although trace impurities in raw materials can impact the experimental reproducibility of high-performance PSCs, the in situ study of how trace impurities affect perovskite film growth is never investigated. Here, light is shed on the impact of inevitable water contamination in lead iodide (PbI2 ) on the replicability of device performance, mainly depending on the synthesis methods of PbI2 . Through synchrotron-based structure characterization, it is uncovered that even slight additions of water to PbI2 accelerate the crystallization process in the perovskite layer during annealing. However, this accelerated crystallization also results in an imbalance of charge-carrier mobilities, leading to a degradation in device performance and reduced longevity of the solar cells. It is also found that anhydrous PbI2 promotes a homogenous nucleation process and improves perovskite film growth. Finally, the PSCs achieve a remarkable certified power conversion efficiency of 24.3%. This breakthrough demonstrates the significance of understanding and precisely managing the water content in PbI2 to ensure the experimental replicability of high-efficiency PSCs.

Lattice Distortion and Low-Frequency Anharmonic Phonons Suppress Charge Recombination in Lead Halide Perovskites upon Pseudohalide Doping: Time-Domain Ab Initio Analysis.

Perovskite solar cells have witnessed a surge in interest as a promising technology for low-cost, high-efficiency photovoltaics with certified power conversion efficiencies beyond 25%. However, their commercial development is hindered by poor stability and nonradiative losses that restrict their approach to the theoretical efficiency limit. Using ab initio nonadiabatic molecular dynamics, we demonstrate that nonradiative charge recombination is suppressed when the iodide in formamidinium lead iodide (FAPbI3) is partially replaced with pseudohalide anions (SCN-, BF4-, and PF6-). The replacement breaks the symmetry of the system and creates local structural distortion and dynamic disorder, decreasing electron-hole overlap and nonadiabatic electron-vibrational coupling. The charge carrier lifetime is found to increase with increased structural distortion and is the longest for PF6-. This work is fundamentally relevant to the design of high-performance perovskite materials for optoelectronic applications.

A Comprehensive Guide to Bifacial Perovskite Solar Cells: Simulation and Optimization

AbstractBifacial perovskite solar cells (PSCs) have received much attention from researchers and scientists. Recently, a certified power conversion efficiency (PCE) of 21.40% (front illumination) and 20.01% (rear illumination) of bifacial PSC has shown immense potential to take over the photovoltaic industry. However, the PCE bifacial PSCs still have a long way to go, as compared to their mono‐facial PSCs counterparts (PCE 26.1%). This gap in the performance level propels us to get more insight into the device physics of bifacial PSCs. In this work, bifacial PSCs are simulated and optimized by selecting an appropriate choice of the electron transport layer (ETL) and hole transport layer (HTL). In this study, it is found that the conduction band offset (CBO) and valance band offset (VBO) play a vital role in choosing a proper charge‐selective layer. The band alignment highly affects the Shockley‐Read‐Hall (SRH) recombination rate and consequently, the device performance. The bandgap of the rear transparent electrode (RTE) plays a vital role in photo‐absorption and band alignment at the HTL/RTE interface and hence the device performance. This investigation reveals that the perovskite absorber material should be intrinsic in semiconducting nature to achieve a higher bifacial factor from the device.

Stabilized hole-selective layer for high-performance inverted p-i-n perovskite solar cells.

P-i-n geometry perovskite solar cells (PSCs) offer simplified fabrication, greater amenability to charge extraction layers, and low-temperature processing over n-i-p counterparts. Self-assembled monolayers (SAMs) can enhance the performance of p-i-n PSCs but ultrathin SAMs can be thermally unstable. We report a thermally robust hole-selective layer comprised of nickel oxide (NiOx) nanoparticle film with a surface-anchored (4-(3,11-dimethoxy-7H-dibenzo[c,g]carbazol-7-yl)butyl)phosphonic acid (MeO-4PADBC) SAM that can improve and stabilize the NiOx/perovskite interface. The energetic alignment and favorable contact and binding between NiOx/MeO-4PADBC and perovskite reduced the voltage deficit of PSCs with various perovskite compositions and led to strong interface toughening effects under thermal stress. The resulting 1.53-electron-volt devices achieved 25.6% certified power conversion efficiency and maintained >90% of their initial efficiency after continuously operating at 65 degrees Celsius for 1200 hours under 1-sun illumination.

Thioacetamide‐Assisted Crystallization of Lead‐Free Perovskite Solar Cells for Improved Efficiency and Stability

Perovskite solar cells (PSCs) have made great strides in recent years, operating inside the theoretical Scholkely–Quisser efficiency limit with a certified power conversion efficiency (PCE) of 26.1%. However, lead toxicity from Pb‐based PSCs can harm the environment. As a result, the search for nontoxic and environmentally friendly substances to replace Pb in perovskites is the need of the hour. Tin has emerged as the most viable choice to replace Pb, due to its favorable electronic properties and smaller bandgaps of Sn‐based perovskites between 1.1 and 1.4 eV, strong charge carrier mobility, and high theoretical efficiency of 32%. Sn vacancies and point defects, on the other hand, are easily produced in Sn perovskites, leading to nonradiative recombination. Furthermore, interfacial flaws and traps impede further performance improvement. In this research, to produce high‐quality Pb‐free perovskites for high‐performance PSCs, a Lewis‐base thioacetamide (TAA) is added to the simple FASnI3 perovskite solution. FASnI3 and TAA additive‐based films effectively control perovskite film crystallinity and grain size via Lewis acid–base reaction. The champion FASnI3 + TAA‐based PSC achieves a maximum PCE of 10.67% while paving a facile way for other compositional perovskite analogues to be integrated into highly efficient and operationally stable PSCs.

Recent Progress of Inorganic Hole‐Transport Materials for Perovskite Solar Cells†

Comprehensive SummaryPerovskite solar cells (PSCs) have achieved significant progress in the past decade and a certified power conversion efficiency (PCE) of 26.0% has been achieved. The widely used organic hole transport materials (HTMs) in PSCs are typically sensitive to the moisture environment and continuous light exposure. In contrast, the inorganic HTMs benefiting from their outstanding merits, such as excellent environmental stability, are considered as alternatives and have attracted much attention in PSCs. In this review, we provide a comprehensive summary of the fundamental properties and recent progress of inorganic HTMs in n‐i‐p and p‐i‐n structured PSCs. Additionally, we emphasize the importance of inorganic HTMs in the development of highly efficient and stable PSCs.