Inverted Device Structure Research Articles

Optimization of laser patterning process for eco-friendly tin-halide perovskite solar module – with a nanosecond green laser

The tin-based perovskite solar cells are promising future eco-friendly photovoltaic technology with increasing efficiency, which relies on fluorine-doped tin oxide (FTO) or indium tin oxide (ITO) as a transparent conducting oxide (TCO) for front contact. In the monolithic module fabrication process interconnections are executed by a series of three scribes with two different lasers 1064 nm and 532 nm. This study aims to simplify the interconnection process in tin-based perovskite solar modules by using a single visible laser source to perform all three scribes. The study uses an inverted device structure of Glass/TCO/ Poly(3,4-ethylenedioxythiophene): Polystyrene sulfonate (PEDOT: PSS)/Formamidinium-tin-iodide (FASnI3)/C60/Bathocuproine (BCP)/Ag and a 532 nm nanosecond pulsed laser source to pattern the ITO and FTO (P1 scribe), the PEDOT: PSS/FASnI3/C60/BCP stack (P2 scribe), and the PEDOT: PSS/FASnI3/C60/BCP/Ag (P3 scribe). The quality of the P1 scribe is assessed by examining the edges, completeness of film removal, cracking, film delamination, and elemental mapping using a stylus profiler, optical microscope, and energy dispersive x-ray spectroscopy. The P1 scribe is completely removed with line widths of 70 µm and 110 µm of ITO and FTO, respectively, without damage to the glass substrate. The profiles are steep, and the electrical isolation is greater than 40 MΩ. The same 532 nm laser is used for P2 and P3 scribes. The ablation of PEDOT: PSS during P2 and P3 scribe is studied by Raman spectroscopy. The results show that the use of a single 532 nm laser source can simplify the patterning process of monolithic tin-based perovskite solar modules, and potentially reduce production costs.

Simulation and optimization of 30.17% high performance N-type TCO-free inverted perovskite solar cell using inorganic transport materials

Perovskite solar cells (PSCs) have gained much attention in recent years because of their improved energy conversion efficiency, simple fabrication process, low processing temperature, flexibility, light weight, and low cost of constituent materials when compared with their counterpart silicon based solar cells. Besides, stability and toxicity of PSCs and low power conversion efficiency have been an obstacle towards commercialization of PSCs which has attracted intense research attention. In this research paper, a Glass/Cu2O/CH3NH3SnI3/ZnO/Al inverted device structure which is made of cheap inorganic materials, n-type transparent conducting oxide (TCO)-free, stable, photoexcited toxic-free perovskite have been carefully designed, simulated and optimized using a one-dimensional solar cell capacitance simulator (SCAPS-1D) software. The effects of layers’ thickness, perovskite’s doping concentration and back contact electrodes have been investigated, and the optimized structure produced an open circuit voltage (Voc) of 1.0867 V, short circuit current density (JSC) of 33.4942 mA/cm2, fill factor (FF) of 82.88% and power conversion efficiency (PCE) of 30.17%. This paper presents a model that is first of its kind where the highest PCE performance and eco-friendly n-type TCO-free inverted CH3NH3SnI3 based perovskite solar cell is achieved using all-inorganic transport materials.

High Performance Organic Solar Cells Prepared with Bi‐Triangular Pyramidal Organic Phosphonium Interface Material

AbstractNowadays, amine containing electrode interface material destroy the non‐fullerene acceptor becomes a hard nut to crack for organic solar cells. Developing water‐soluble interface material which is no chemical reaction with non‐fullerene acceptor is an important research theme. Here, we report two bi‐triangular pyramidal electronic configuration organic‐phosphonium bromides as non‐amine cathode interfacial layer for fabricating high‐efficiency stable organic solar cells. The power conversion efficiency (PCE) of inverted device structure with PBDB‐T/ITIC as active layer is up to 11.58 % which is great larger than control device PCE (9.35 %). Same device structure with PM6/Y6 as active layer, the PCE is up to 15.26 % and also is dramatically higher than the referred device PCE 14.36 %. Meanwhile, the devices show greatly improved stability by organic‐phosphonium bromide interlayer.

Rapid Evaporation of a Metal Electrode for a High-Efficiency Perovskite Solar Cell.

Organic-inorganic hybrid perovskite solar cells (PSCs) have attracted considerable attention due to the excellent optoelectronic properties of perovskite materials. The energy consumption and high cost issues of metal electrode evaporation should be addressed before large-scale manufacturing and application. We developed an effective metal electrode evaporation procedure for the fabrication of high-efficiency planar heterojunction (PHJ) PSCs, with an inverted device structure of glass/indium tin oxide (ITO)/poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA)/perovskite/[6,6]-phenyl-C61-butyric acid methyl ester (PCBM)/(E)-β-caryophyllene (BCP)/Ag. The effect of the evaporation rate for an evaporator with a small-volume metal cavity on the performance of PHJ-PSC devices was investigated systematically. Through controlling the processes of Ag electrode evaporation, the charge dynamics of the devices were studied by analyzing their charge recombination resistance and lifetime, as well as their defect state density. Our findings reveal that the evaporation rate of an evaporator with a small cavity is favorable for the performance of PHJ-PSCs. As a result, PHJ-PSCs fabricated using a very thin, non-doped PTAA film exhibit photoelectric conversion efficiency (PCE) of 19.21%, with an open-circuit voltage (Voc) of 1.132 V. This work showcases the great potential of rapidly evaporating metal electrodes to reduce fabrication costs, which can help to improve the competitiveness in the process of industrialization.

Chiral Helical Polymer‐Induced Efficient Circularly Polarized Organic Light‐Emitting Diodes

AbstractCircularly polarized organic light‐emitting diodes (CP‐OLEDs) have attracted tremendous attention, but constructing CP‐OLEDs with both high electroluminescence dissymmetry factors (gEL) and good device performance remains a big challenge. The present work reports the first CP‐OLEDs by using chiral helical polymers as inducers to trigger efficient CP electroluminescence from achiral conjugated polymers. The successful preparation of CP‐OLEDs based on two chiral helical polymers further demonstrates the universality of the established strategy. Benefiting from the high helical twisting power of the chiral helical polymer, a maximum |gEL| value of 2.0 × 10−2 is obtained in the resulting CP‐OLEDs. Moreover, by adopting an inverted device structure, the device performance of the CP‐OLEDs is significantly improved, with a maximum brightness of 49340/51973 cd m−2, high current efficiency of 5.62/5.44 cd A−1, and low turn‐on voltage of 3.1/3.1 V, respectively. The work offers new insights into fabricating CP‐OLEDs by taking advantage of chiral helical polymers.

Efficient and Stable OLEDs with Inverted Device Structure Utilizing Solution‐Processed ZnO‐Based Electron Injection Layer

AbstractTo realize low‐cost, efficient, and stable organic light‐emitting diodes (OLEDs) in future large area displays and lighting, the development of suitable solution‐processed functional materials is highly desirable. Herein, a series of efficient and stable OLEDs with an inverted device architecture is reported, employing both a vapor‐deposited phosphorescent aggregate emitter, i.e., Pd(II) 7‐(3‐(pyridine‐2‐yl‐κN)phenoxy‐κC)(benzo‐κC)([c]benzo[4,5]imidazo‐κN)[1,2‐a][1,5]naphthyridine, and a solution‐processed ZnO layer as potential electron injection layer and electron‐transporting layer. One of the optimized OLED devices exhibits its peak external quantum efficiency (EQE) of 23.9% and retains EQEs of 23.5% and 18.7% at 1000 and 10 000 cd m−2, with a low efficiency roll‐off. Such an efficient device also demonstrates a measured lifetime (LT95) of 98.6 h with an initial brightness of 10 435 cd m−2 corresponding to an estimated LT95 of 5313 h at 1000 cd m−2. By depositing a 2 nm Al on the ZnO surface, an estimated LT95 at 1000 cd m−2 of such a device can be further extended to 73 244 h, making it the longest‐lived OLED reported in the literature domain. This study lays the strong foundation for the future deployment of efficient and stable inverted OLEDs with solution‐processed ZnO layers for a wide range of displays and lighting applications.

Solution-Processable NiOx:PMMA Hole Transport Layer for Efficient and Stable Inverted Organic Solar Cells.

For organic solar cells (OSCs), nickel oxide (NiOx) is a potential candidate as the hole transport layer (HTL) material. However, due to the interfacial wettability mismatch, developing solution-based fabrication methods of the NiOx HTL is challenging for OSCs with inverted device structures. In this work, by using N, N-dimethylformamide (DMF) to dissolve poly(methyl methacrylate) (PMMA), the polymer is successfully incorporated into the NiOx nanoparticle (NP) dispersions to modify the solution-processable HTL of the inverted OSCs. Benefiting from the improvements of electrical and surface properties, the inverted PM6:Y6 OSCs based on the PMMA-doped NiOx NP HTL achieves an enhanced power conversion efficiency of 15.11% as well as improved performance stability in ambient conditions. The results demonstrated a viable approach to realize efficient and stable inverted OSCs by tuning the solution-processable HTL.

Conventional and Inverted Light-Emitting Diodes with 386 nm Emission Wavelength Based on Metal-Free Carbon Dots

Ultraviolet (UV) light-emitting diodes (LEDs) are of great concern due to wide applications in the fields of solid-state displays, photocommunication, and scientific and medical instruments. During the past 10 years, organic and inorganic semiconductors have made great breakthroughs in short-wavelength emission. Nowadays, carbon dots (CDs), which possess distinctive superiorities of high stability, nontoxicity, and low cost, are promising all-band emission materials for the next generation of LEDs. However, the fabrication of CD-based LEDs (CD-LEDs) with emission wavelengths below 400 nm is still a huge limitation in this field. Herein, we prepared UV emission CDs with the photoluminescence emission wavelength of 371 nm. The UV-CDs are perfectly compatible with both conventional and inverted device structures so as to realize the currently shortest electroluminescent emission wavelength of 386 nm for CD-LEDs. The conventional UV-CD-LEDs possess the optimum luminance of 268 cd m-2 (5427 W sr-1 m-2) with an external quantum efficiency (EQE) of 1.115%. Meanwhile, the inverted UV-CD-LEDs possess the optimum luminance of 132 cd m-2 (2673 W sr-1 m-2) with an EQE of 0.869%. This work paves a new road to manufacture carbon nanomaterial-based UV emission devices with high luminance, EQE, and stability.

Understanding the Composition of Layer‐by‐Layer Deposited Active Layer at Buried Bottom Surface

AbstractLayer‐by‐layer (LbL) coating is becoming a widely used method to fabricate nonfullerene active layer films for organic solar cells. However, the vertical compositional distribution of the LbL‐coated active layer, particularly at the buried bottom surface, is not clear yet. In common sense, it is believed that the LbL‐coating yields a donor–mixture–acceptor (D–m–A) vertical distribution in the active layer, i.e., a thin polymer donor layer at the bottom surface, a thin acceptor layer at the top surface and a donor‐acceptor mixture in the middle. In this study, it is shown that the LbL active layer vertically is an entire donor:acceptor mixture. A pure layer of polymer donor doesn't exist at the bottom surface. The LbL active layer delivers high performance in both conventional and inverted device structures. A thin polymer layer with different thicknesses (2, 6, 12 nm) is inserted at the bottom surface to study their effects on the device performance. Those inserted layers substantially deteriorate the device's performance. Furthermore, the assumption is further confirmed by X‐ray photoelectron spectroscopy measurement on the exposed “originally buried” surface. This study sheds light on understanding the vertical compositional distribution of active layer via layer‐by‐layer solution processing.

High-Performance Inverted Organic Solar Cells via the Incorporation of Thickness-Insensitive and Low-Temperature-Annealed Nonconjugated Polymers as Electron Transport Materials.

Developing new electron transport layers has been an effective way to fabricate high-performance bulk-heterojunction organic solar cells (OSCs). Resolving the longstanding problems associated with commonly used zinc oxide (ZnO), such as electron traps and light-induced device deterioration, however, is still a great challenge. In this study, glycerol diglycidyl ether (GDE) and 1,4-butanesultone (BS) are blended with polyethyleneimine (PEI) to produce cross-linkable PEI-based materials, PEI-GDE and PEI-GDE-BS, which can function as alternative electron transport layers to replace conventional ZnO cathode-modifying layers in inverted OSCs. PEI-GDE and PEI-GDE-BS are amendable to low-temperature annealing processes to produce cross-linked films. The inverted device structure of ITO/ETL/PM6:BTP-BO-4F:PC71BM/MoO3/Ag was used to evaluate the effects of incorporating PEI-GDE and PEI-GDE-BS as electron transport materials. Compared with ZnO-based devices, the PEI-GDE- and PEI-GDE-BS-based devices exhibit significant improvements in photovoltaic performances due to smoother surface roughness, higher charge collection and exciton dissociation efficiencies, higher electron mobilities, and stronger π-π interactions. In particular, a PEI-GDE-BS-based device shows an outstanding power conversion efficiency (PCE) of 17.55% with a VOC of 0.83 V, a JSC of 27.88 mA/cm2, and an FF of 75.96%, which offers great possibilities in the applications of flexible solar cells.

Minimizing the Voltage Deficit of Tin Halide Perovskite Solar Cells with Hydroxyurea‐Doped PEDOT:PSS

Tin halide perovskite solar cells (TPSCs) have made great strides recently with an inverted device structure, in with poly(3,4‐ethylenedioxythiphene):poly(styrenesulfonate) (PEDOT:PSS) has been already widely applied as the hole transport layer (HTL) due to its optical transparency, easy processability, and good mechanical expandability. Nevertheless, the TPSCs still suffer from a severe voltage deficit from the carrier recombination loss and energy‐level mismatch. Herein, hydroxyurea (HYU)‐doped PEDOT:PSS to suppress the voltage loss at the PEDOT:PSS/perovskite interface is applied. It has been revealed that HYU effectively tunes the conductivity and hole mobility of PEDOT:PSS. The interfacial nonradiative carrier recombination is effectively suppressed. The target device shows a 20% increase in the open‐circuit voltage together with an increased power conversion efficiency rising from 8.10% to 10.17%. Therefore, this work provides a feasible strategy to minimize the voltage deficit in TPSCs from the HTL side, which is highly important to further boost the performance of TPSCs.

Enhanced Electroluminescence via a Nanohybrid Material Consisting of Aromatic Ligand-Modified InP Quantum Dots and an Electron-Blocking Polymer as the Single Active Layer in Quantum Dot-LEDs.

Electron overcharge causes rapid luminescence quenching in the quantum dot (QD) emission layer in QD light–emitting diodes (QD–LEDs), resulting in low device performance. In this paper we describe the application of different aromatic thiol ligands and their influence on device performance as well as their behavior in combination with an electron blocking material (EBM). The three different ligands, 1–octanethiol (OcSH), thiophenol (TP), and phenylbutan–1–thiol (PBSH), were introduced on to InP/ZnSe/ZnS QDs referred to as QD–OcSH, QD–TP, and QD–PBSH. PBSH is in particular applied as a ligand to improve QD solubility and to enhance the charge transport properties synergistically with EBM probably via π–π interaction. We synthesized poly-[N,N-bis[4-(carbazolyl)phenyl]-4-vinylaniline] (PBCTA) and utilized it as an EBM to alleviate excess electrons in the active layer in QD–LEDs. The comparison of the three QD systems in an inverted device structure without the application of PBCTA as an EBM shows the highest efficiency for QD–PBSH. Moreover, when PBCTA is introduced as an EBM in the active layer in combination with QD–PBSH in a conventional device structure, the current efficiency shows a twofold increase compared to the reference device without EBM. These results strongly confirm the role of PBCTA as an EBM that effectively alleviates excess electrons in the active layer, leading to higher device efficiency.

Optimization based on computational analysis of lead-free inverted planar photo-voltaic device structure using halide based double perovskite material

Owing to the appealing optoelectrical, mechanical, and physical properties, configurable bandgaps, good performance on opaque devices, and low manufacturing cost, Perovskites solar cells are found to be the best alternatives for semi-transparent photo-voltaic (PV) applications. The high absorption coefficient, high carrier mobility, and long carrier diffusion length are inherent features of many organic and inorganic halide perovskite solar cells. Most of the promising perovskite materials contain Lead (Pb) and hence they are toxic. Besides toxicity issues, the stability of these perovskite structures is another key challenge in the process of its commercial production. The performance of various lead-free active PV materials was studied and identified that Cesium–Titanium Halide materials can be a suitable alternate for lead-based perovskite materials. These promising Cs2TiX6 materials have a tunable bandgap between 1.4 eV and 2.3 eV and have balanced electron and hole diffusion lengths. Most of the conventional PSC structure consists of regular planar N-I-P structure and the commercial applications of such devices are bounded due to very high J-V hysteresis and the need for high temperature during fabrication. The primary objective of this work is to optimize and develop an eco-friendly, highly efficient, Cesium-Titanium based novel inverted PV cell structure with all in-organic charge transport materials. The solar cell simulation program, SCAPS – 1D simulator, was used for conducting the numerical study and tested various device structures for obtaining maximum efficiency. The variations in the performance of PV cell structure were analyzed while using assorted absorber materials and inorganic charge transport materials. After the SCAPS-1D based simulation study, a high-performance PSC structure, FTO / MoO3 / Cs2TiBr6 / SnO2 / Au, was obtained. The proposed inverted PV cell structure can produce an excellent power conversion efficiency of 15.68 %, short-circuit current density of 16.59 mA/cm2, an open circuit voltage of 1.1 V, and a fill-factor of 85.76 %.

The hydrothermal synthesis of blue-emitting boron-doped CQDs and its application for improving the photovoltaic parameters of organic solar cell.

In this work, boron-doped CQDs (B-CQDs) were synthesized by using boric acid, urea, and citric acid via hydrothermal method to use as a novel additive material for poly(3-hexylthiophene-2,5-diyl) (P3HT):[6,6]-phenyl-C61-butyric acid methyl ester (PCBM) based organic solar cells. The OSCs with an inverted device structure were fabricated on titanium dioxide (TiO2) thin film. It was showed the crystallinity, morphological and optical properties of P3HT:PCBM films improved after B-CQDs additive. The best performance was obtained to be a 39.65% of FF, a 546 mV of Voc, an 8.606 mA cm-2 of Jsc after 3 vol.% B-CQDs addition in P3HT:PCBM blend. The power conversion efficiency (PCE) enhanced from 1.72% (non-doped device) to 2.33% (3% of B-CQDs) (a ~ 35% increase). The obtained results provided that B-CQDs are promising materials to improve the performance of solar cell applications. The novelty of this work is to improve the performance of OSCs using cost-effective and eco-friendly Boron CQDs as an additive. Besides, to achieve a good PCE of OSCs, it is necessary for utilized clean and green energy.

Vertical Distribution in Inverted Nonfullerene Polymer Solar Cells by Layer‐by‐Layer Solution Fabrication Process

The layer‐by‐layer (LBL) solution process is a potential technology for future application of polymer solar cells (PSCs), while the vertical composition distribution evolution of the LBL active layer is still unknown. In this work, taking advantage of the LBL method and inverted device structure, inverted LBL‐processed PSCs are fabricated with polymer donor PM6 and nonfullerene small‐molecule acceptor Y6. As‐prepared devices with PM6 as the bottom layer and Y6 as the top layer exhibit low power conversion efficiencies (PCEs), while the post‐treatment brings a significant boost on the device performance (from 8.5% to 14.4%). The vertical composition distribution evolution of LBL photoactive layer is investigated by the combination of surface atom distribution analysis via X‐ray photoemission spectroscopy (XPS) and composition distribution across the bulk of the films via neutron reflectivity (NR). The findings can potentially offer positive guidance for the further utilization of organic photovoltaics.

Organic Thin‐film Solar Cells Using Benzotrithiophene Derivatives Bearing Acceptor Units as Non‐Fullerene Acceptors

AbstractNew star‐shaped non‐fullerene acceptors (5Z,5′Z,5′′Z)‐5,5′,5′′‐((benzo[1,2‐b : 3,4‐b′ : 5,6‐b′′]trithiophene‐2,5,8‐triyltris(4‐octylthiophene‐5,2‐diyl))tris(methaneylylidene))tris(3‐octyl‐2‐thioxothiazolidin‐4‐one) (1: BTT‐OT‐ORD) and 2,2′,2′′‐((5Z,5′Z,5′′Z)‐((benzo[1,2‐b : 3,4‐b′ : 5,6‐b′′]trithiophene‐2,5,8‐triyltris(4‐octylthiophene‐5,2‐diyl))tris(methaneylylidene))tris(3‐octyl‐4‐oxothiazolidine‐5,2‐diylidene))trimalononitrile (2: BTT‐OT‐OTZDM) with a benzotrithiophene core, alkyl‐thiophen units, and acceptor units were designed and synthesized. The HOMO‐LUMO levels of 1 and 2 were determined by photoemission spectroscopy and UV‐Vis absorption spectroscopy. Binary blend and ternary blend bulk heterojunction (BHJ) organic solar cells with non‐fullerene acceptors 1 and 2 were fabricated with the inverted device structures of glass/ITO/ZnO/active_layer/MoO3/Ag. Both binary blend BHJ solar cells with 1 and 2 show lower JSC and larger VOC values than P3HT : PCBM solar cells. On the other hand, ternary blend BHJ organic solar cells, including 10 % of 1, exhibited a larger power conversion efficiency than P3HT : PCBM solar cells because the JSC value was largely improved.

A-site tailoring in the vacancy-ordered double perovskite semiconductor Cs2SnI6 for photovoltaic application

Air-stable caesium tin iodide (Cs2SnI6) double perovskite are highly desirable for substituting the lead-based halide perovskite solar cells. In this work, we have investigated the effect of A-site tailoring in Cs2SnI6 by adding monovalent cation (Rb and Ag) on film growth properties, (morphology, structural properties, opto-physical properties), optoelectronic properties, and device characteristics. The crystal analysis suggests that the A-site additives suppress CsI secondary phase in (Cs1-xAx)2SnI6 film for x<0.5 whereas multiple secondary phases occur in higher additive content. The opto-physical properties reveal a small change in bandgap energy for alloyed film and excellent thermal stability in ambient air. The inverted device structure ITO/CuI/Cs2SnI6-alloyed/PCBM/AZO/Ag, for the first time, demonstrated the improvement in device parameters (with VOC~ 0.38 V and efficiency of ~0.66%) for the alloyed films. The capacitance analysis reveals that the high defect density in bulk as well as at the interface (Nt>1019 cm−3) has a deleterious effect on the device performance. In this work, we underline insight into the A-site tailoring of Cs2SnI6 double perovskite and the dominant limiting factors for getting high device performance.

Cross-Linkable and Alcohol-Soluble Pyridine-Incorporated Polyfluorene Derivative as a Cathode Interface Layer for High-Efficiency and Stable Organic Solar Cells.

Device performance and commercialization of organic solar cells (OSCs) are strongly influenced by the characteristics of the interface layers. Cross-linked polymer interface layers with solvent-resistant properties are very compatible with large-area solution-processing methods of OSCs and may be beneficial to the environmental stability of OSCs due to the viscoelastic and cross-linked characteristics of the cross-linked polymer. In this work, a novel cross-linkable and alcohol-soluble pyridine-incorporated polyfluorene derivative, denoted as PFOPy, is synthesized and used as a cathode interface layer (CIL) in OSCs. For PFOPy, the pendant epoxy group can be effectively cross linked through cationic polymerization under thermal treatment and the pendant pyridine group can offer good alcohol solubility. Optical absorption tests of PFOPy films before/after washing by chloroform demonstrate the excellent solvent-resistance property for the cross-linked PFOPy film. Compared with the typical ZnO CIL, the cross-linked PFOPy CIL can also substantially reduce ITO's work function and form a better interface contact with the active layer. Utilizing an inverted device structure and a typical active layer of PM6:Y6, ZnO-based OSCs display an optimal power conversion efficiency (PCE) of 15.83% while PFOPy-based OSCs exhibit superior photovoltaic performance with an optimal PCE of 16.20%. Moreover, ZnO-based and PFOPy-based OSCs separately maintain 89% and 90% of the corresponding initial PCE after 12 h of illumination, indicating similarly excellent photostability. More importantly, after 26 complete thermal cycles, ZnO-based OSCs only maintain 81% of the initial PCE while PFOPy-based OSCs retain 92% of the initial PCE and exhibit obviously better thermal cycling stability, indicating that the cross-linked PFOPy CIL should offer stronger interface robustness against thermal cycling stress due to the viscoelastic and cross-linked characteristics of PFOPy. The impressive results indicate that the cross-linked PFOPy CIL would be a very promising CIL in OSCs.

Solution-processed NiO x nanoparticles with a wide pH window as an efficient hole transport material for high performance tin-based perovskite solar cells

The development of tin-based perovskite solar cells (PSCs) is a promising approach to meet the demand of eco-friendly, lead-free perovskite photovoltaics. Limited to the poor chemical stability of tin perovskites, tin-based PSCs usually have to be fabricated with an inverted device structure and both the device efficiency and stability are highly dependent on the selection of hole transport materials (HTMs). Here, we report the synthesis of inorganic nickel oxide (NiO x ) nanoparticles (NPs) via a soft base precipitation method, which enables us to obtain highly dispersed NiO x NPs over a wide pH window. The as-prepared NiO x NPs are employed as the HTM for formamidinium tin iodide (FASnI3) PSCs, resulting in excellent device efficiency (∼8%) and stability (1200 h). Our study offers a facile strategy for mass production of NiO x NPs and easy access to efficient and robust inorganic HTMs that could further boost the development of high performance tin-based PSCs.

Organic–inorganic doped nickel oxide nanocrystals for hole transport layers in inverted polymer solar cells with color tuning

Nickel oxide nanoparticles in alcoholic solutions were developed for processing hole transport layers in non-fullerene acceptor-based solar cells using inverted device structures.