Solar Cell Materials Research Articles

Efficient doping of Spiro-OMeTAD by NO2

Doping of 2,2′,7,7′-tetrakis(N,N-di-4-methoxyphenylamino)-9,9′-spirobifluorene(Spiro-OMeTAD), which is the most common used hole transport material in perovskite solar cells, is widely studied. Especially, bis(trifluoromethane)sulfonamide (Li-TFSI) combined with 4-tert-butylpyridine (TBP) is the most studied dopant to improve the conductivity of Spiro-OMeTAD, with conductivity around 6×10−8 S/cm. In this study, we employed a new oxidizing agent NO2 to dop the Spiro-OMeTAD simply by vapor exposure, showing efficient doping with conductivity up to 2.53×10−3 S/cm and excellent film quality. The doping mechanism was further analyzed by ultraviolet-visible-near infrared spectroscopy (UV-Vis-NIR), electron paramagnetic resonance spectroscopy (EPR), Fourier infrared absorption spectroscopy (TFIR), and X-ray photoelectron spectroscopy. Our findings highlight the potential of molecular doping with NO2 to significantly improve the conductivity of Spiro-OMeTAD, providing a deep understanding of the doping effects on Spiro-OMeTAD.

Exploring the potential of end-capping acceptor designing on highly soluble and efficient Schiff-based Hole-Transporting materials for High-Efficiency perovskite solar cells

Photovoltaic materials, especially perovskite solar cells (PSCs) are promising candidates for rising global energy demands. Here, five phenothiazine-based hole-transporting materials (AZOM1, AZOM2, AZOM3, AZOM4, and AZOM5) are designed by Schiff base chemistry with A-π-D-π-A framework for PSCs. We executed density functional theory calculations to explore the electronic, photo-physical, photovoltaic, and charge-transporting properties of the studied hole-transporting materials (HTMs). Our results indicate that AZOM1-AZOM5 HTMs possess more negativeHOMO energies (−5.64 to − 5.49 eV), lower bandgaps, and superior solubility as compared to Spiro-OMeTAD (HOMO energy = − 4.47 eV) and reference AZO-II (HOMO energy = − 4.68 eV), which enhanced their hole extraction and open-circuit photo-voltage (VOC). The transition density matrix and hole-electron distribution analyses show that AZOM1- AZOM5 molecules have ultrafast charge transmission, low overlapping between holes and electrons, and a higher dissociation rate than the Spiro-OMeTAD and AZO-II HTMs. The designed HTMs have smaller exciton binding energies than the Spiro-OMeTAD and AZO-II, allowing electron-hole pairs to dissociate into positive and negative charges smoothly. AZOM1-AZOM5 HTMs have higher hole charge transfer integral than the AZO-II, facilitating high hole mobility in PSCs. All designed HTMs have higher VOC (1.49 to 1.64 V) and lower energy losses (0.63 to 1.03 eV) than the Spiro-OMeTAD and AZO-II HTMs. Moreover, the AZOM1-AZOM5 HTMs demonstrated deeper HOMO energies, high solubility, more stability, and high open-circuit photo-voltages than the recently reported HTMs at “MPW1PW91/6-31G (d, p)” level of theory. Overall, the AZOM1-AZOM5 HTMs are very effective in boosting the solubility, charge-transporting ability, and efficiency of PSCs.

Novel 2D heterostructure composites of V2C MXene/TiO2 and graphene/TiO2 for platinum replacement in dye-sensitized solar cells

This study evaluates the potential of V2C MXene/TiO2 and Graphene/TiO2 composites as alternatives to platinum for counter-electrodes in dye-sensitized solar cells (DSSCs). V2C MXene was synthesized by selectively etching the aluminum layer from V2AlC MAX phase powder, resulting in multilayered V2C MXene. The layered morphologies of MXene and graphene were confirmed via Scanning Electron Microscopy (SEM), while their crystalline structures were validated using X-ray diffraction (XRD) analysis. SEM analysis confirmed the delaminated layered structure of graphene and the distinct layers of V2C MXene. XRD findings showed that MXene has significantly greater interlayer spacing than graphene, offering more catalytic sites for charge injection. Electrocatalysts were prepared by incorporating TiO2 paste with MXene and graphene, with TiO2 serving as a binder. These composites were then employed as counter-electrode materials in dye-sensitized solar cells. The MXene-based counter electrode achieved a photoconversion efficiency of 1.625 %, surpassing graphene-based (1.149 %) and Pt-based (1.567 %) counterparts under standard illumination. The efficiency of cells was meticulously characterized over an extended period. The results indicated that the efficiency of these cells remained stable over time. This stability suggests that MXene/TiO2 and Graphene/TiO2 based catalysts are robust and do not degrade with time.

Scanning Probe Microscopy of Halide Perovskite Solar Cells.

Scanning probe microscopy (SPM) has enabled significant new insights into the nanoscale and microscale properties of solar cell materials and underlying working principles of photovoltaic and optoelectronic technology. Various SPM modes, including atomic force microscopy, Kelvin probe force microscopy, conductive atomic force microscopy, piezoresponse force microscopy, and scanning near-field optical microscopy, can be used for the investigation of electrical, optical and chemical properties of associated functional materials. A large body of work has improved the understanding of solar cell device processing and synthesis in close synergy with SPM investigations in recent years. This review provides an overview of SPM measurement capabilities and attainable insight with a focus on recently widely investigated halide perovskite materials.

Polymers Containing Phenothiazine, Either as a Dopant or as Part of Their Structure, for Dye-Sensitized and Bulk Heterojunction Solar Cells.

Potential photovoltaic technology includes the newly developed dye-sensitized solar cells (DSSCs) and bulk heterojunction (BHJ) solar cells. Owing to their diverse qualities, polymers can be employed in third-generation photovoltaic cells to specifically alter their device elements and frameworks. Polymers containing phenothiazine, either as a part of their structure or as a dopant, are easy and economical to synthesize, are soluble in common organic solvents, and have the potential to acquire desired electrochemical and photophysical properties by mere tuning of their chemical structures. Such polymers have therefore been used either as photosensitizers in dye-sensitized solar cells, where they have produced power conversion efficiency (PCE) values as high as 5.30%, or as donor or acceptor materials in bulk heterojunction solar cells. Furthermore, they have been employed to prepare liquid-free polymer electrolytes for dye-sensitized and bulk heterojunction solar cells, producing a PCE of 8.5% in the case of DSSCs. This paper reviews and analyzes almost all research works published to date on phenothiazine-based polymers and their uses in dye-sensitized and bulk heterojunction solar cells. The impacts of their structure and molecular weight and the amount when used as a dopant in other polymers on the absorption, photoluminescence, energy levels of frontier orbitals, and, finally, photovoltaic parameters are reviewed. The advantages of phenothiazine polymers for solar cells, the difficulties in their actual implementation and potential remedies are also evaluated.

Accelerating the discovery of acceptor materials for organic solar cells by deep learning

It is a time-consuming and costly process to develop affordable and high-performance organic photovoltaic materials. Computational methods are essential for accelerating the material discovery process by predicting power conversion efficiencies (PCE). In this study, we propose a deep learning-based framework (DeepAcceptor) to design and discover highly efficient small molecule acceptor materials. Specifically, an experimental dataset is constructed by collecting acceptor data from publications. Then, a deep learning-based model is customized to predict PCEs by applying graph representation learning to Bidirectional Encoder Representations from Transformers (BERT), with the atom, bond, and connection information in acceptor molecular structures as the input (abcBERT). The computational dataset derived from density functional theory (DFT) calculations and the experimental dataset from literature are used to pre-train and fine-tune the model, respectively. The abcBERT model outperforms other state-of-the-art models for the PCE prediction with MAE = 1.78 and R2 = 0.67 on the test set. A molecular generation and screening process is built to find new high-performance acceptors for PM6. Three discovered candidates are further validated by experiment, and the best PCE reaches 14.61%. The released user-friendly interface of DeepAcceptor greatly boosts the accessibility and efficiency of designing and discovering high-performance acceptors. Altogether, the DeepAcceptor framework with abcBERT is promising to predict the PCE and accelerate the discovery of high-performance acceptor materials.

DFT and SCAPS-1D based optimization study of double perovskite Cs2AuBiCl6 solar cells utilizing different charge transport layers

In this work, halide double perovskite (HDP) Cs2AuBiCl6 is investigated as potential absorber material in the perovskite solar cell (PSC) using the SCAPS-1D tool. WIEN2K code is utilized for computation to study the structural, and optoelectronic properties of Cs2AuBiCl6. The calculated bandgap of the Cs2AuBiCl6 is found to be ∼1.09 eV using TB-mBJ (Tran-Blaha modified Becke-Johnson) potential. Performance of the Cs2AuBiCl6-based PSC is enhanced by improving the properties of charge transport layers and the perovskite (PVSK) absorber layer. Combination of Electron Transport Layers (ETLs) such as WS2, PCBM, ZnO, TiO2, and C60 and Hole Transport Layers (HTLs) such as Cu2O, P3HT, CuSCN, PEDOT: PSS, Spiro-OMeTAD, CuSbS2 are evaluated to find the best ETLs and HTLs among the above-mentioned materials. Also, further study is performed on the five best devices with five different ETLs using CuSbS2 as the HTL. Apart from that, the energy band diagrams of the best five devices are investigated. Further, a performance study is done on those best five devices through the impact of the variations in thickness of ETL, defect density, thickness of Cs2AuBiCl6 layer, shunt, and series resistances of device. After all the optimizations, the best PCEs of these five optimized devices are found to be 21.16 %, 21.14 %, 20.84 %, 20.79 %, and 14.75 % with CuSbS2 as HTL, and C60, WS2, TiO2, PCBM, and ZnO as ETLs, respectively. Furthermore, current density-voltage (J-V) and quantum efficiency (QE) characteristics of the five devices are analyzed to determine the potential of Cs2AuBiCl6 as a viable material for non-leaded PSCs.

An Experimental Assessment of the Performance of Solar Panels Using Efficiency Enhancement Techniques in India's Tropical Region

<p style="text-align:justify"><span style="font-size:11pt"><span style="line-height:normal"><span style="font-family:Calibri,sans-serif"><span lang="EN-US" style="font-size:10.0pt"><span style="color:black">Due to its abundance and lack of pollution, solar energy will soon be the most popular source of electricity production. Numerous factors, including the temperature effect, solar irradiance effect, shadow effect, incident angle effect, dust accumulation on the solar cell, shunt resistance, types of solar cell materials, mechanical defects in the solar panel, spectral mismatch loss, cable loss, maintenance and cleaning cycle, load mismatching effect, etc., harm the efficiency of solar P.V. power generation systems. This study aims to quantify the impact of these factors and explore efficiency enhancement techniques to mitigate their effects. Among the various factors, solar irradiation and temperature significantly influence solar P.V. panel efficiency. This research investigates the effects of solar irradiation, incident angle, and temperature through simulations and experimental methods using two 100W solar panels. Efficiency enhancement techniques like sensor-based sun tracking and temperature cooling systems are incorporated with conventional solar P.V. power generation systems. The experimental results prove that the efficiency enhancement techniques improved the efficiency of solar panels by up to 12% compared to conventional solar panels.</span></span></span></span></span></p>

(Invited) Parameter Prediction in Colloidal Quantum Dot Solar Cells Using Residual Neural Networks Trained on Experimental Data

Colloidal quantum dots (CQDs) are an attractive third-generation material for photovoltaics, especially as infrared materials for multi-junction solar cells. Characterization and materials parameter prediction both play a critical role in the rising efficiencies in this field. However, there are numerous materials properties that need to be measured in order to fully characterize a device, leading to high research costs and slow development times. Here, we leverage recent advancements in machine learning (ML), along with a recently-demonstrated multimodal spectral characterization method [1], to predict complex materials parameters in CQD solar cells from simple current density-voltage (JV) curves, using an algorithm trained on experimental data.[2]Past work ML prediction of materials properties has focused on using simulated data due to the difficulty in collecting enough experimental data to fully train an algorithm. While it is not feasible to fabricate thousands of devices in a typical research lab, it is possible to measure several thousand points on a single device. We used a micrometer-resolution 2D characterization method with millimeter-scale field of view to acquire enough training data using only a handful of devices, while learning the spatial relationships between materials parameters. Photoluminescence, trap state density, transient photovoltage, transient photocurrent, and carrier mobility were predicted (Figure 1) by five different residual neural networks, each using a ResNet block and containing over 300k learnable parameters. The design of the networks were based on the ResNet50 architecture [3]. We also implemented a novel neighborhood approach to reduce errors and account for spatial correlations in device behavior, leading to insights into transport mechanisms and correlation lengths in CQD thin films. This method could be used to study a wide range of material systems and devices, ultimately leading to a universal prediction model that greatly simplifies the characterization process for optoelectronic devices and accelerates development times.

Portrait of a UK-Africa Capacity Building Initiative Consortium 2015-2022: the Cameroon, Ghana, South Africa and United Kingdom Materials Initiative (CaGSUMI) for developing materials for solar cells.

The CaGSUMI consortium was funded by the Royal Society-Department for International Development (later the Foreign, Commonwealth & Development Office) on the Africa Capacity Building Initiative programme between the years 2015 and 2022 and involved three Sub-Saharan African universities: Kwame Nkrumah University of Science and Technology, Kumasi, Ghana, University of Yaoundé I, Cameroon, and the University of Zululand, South Africa; and the University of Manchester in the United Kingdom. The project was used to cement an emergent UK-Africa network in the areas of materials chemistry related to renewable energy generation with both thin films and nanomaterials. The consortium's outputs led to numerous publications of African science in international journals, a number of graduated PhDs who went on to permanent academic positions and prestigious fellowships, the establishment of a capacity-building plan relevant to the chemistry departments in each of the African countries, and the installation of a number of first-in-kind pieces of kit for African laboratories that will keep them on a competitive footing at an international level for the next decade and more.

Understanding different oxidation methods for the hole transport layer Spiro-OMeTAD to improve perovskite solar cell performance

The preparation of a high-performance hole transport layer is a pivotal factor in achieving efficiency and stable perovskite solar cells. 2,2’,7,7’-Tetrakis[N, N-di(4-methoxyphenyl)amino]−9,9’-spirobifluorene (Spiro-OMeTAD) currently stands as the most widely employed hole transport material in high-performance perovskite solar cells. The current methodologies for its preparation primarily revolve around three techniques: O2 oxidation, cobalt salt doping, and CO2 bubbled doping. In this study, we systematically investigated and analyzed Spiro-OMeTAD prepared through these three methods, from solution and film to device. The CO2-bubbled method and Co-doped method allow for faster and more complete oxidation of Spiro-OMeTAD while maintaining conductivity and energy level matching. Therefore, the film of both methods shows better carrier extract capabilities and defect states than that of O2-oxidized. In particular, the film of the CO2-bubbled method had better hydrophobicity and thermal stability, showing the least degradation at 85 °C annealing, which can be attributed to the removal of hydrophilic Li+. This study could inspire further optimization of Spiro-OMeTAD film fabrication processes in perovskite solar cells.

Molecular engineering push-pull structural versatility in the triphenylamine-thienodioxine-based hole transporting materials for high-performance organic and perovskite solar cells

This study proposes a push-pull molecular engineering approach to fabricate versatile hole-transporting materials (HTMs) for photovoltaic cells. Herein, we introduce a D-π-A strategy for fabricating four highly functional small molecules of thienodioxine core-based HTMs (CJ06C1 to CJ06C4), via core functionalization with diversified electron-withdrawing acceptor moieties. The engineered HTMs are evaluated by employing quantum calculations to analyze the structure-property relationships from optoelectronic, electrochemical, and solvability attributes. The findings reveal that acceptor-integrated HTMs unveil excellent band alignment with active perovskite layer with deeper HOMO energy levels (-4.96 eV to 5.02 eV), transparency in the visible portion λmaxabs<521, which entail appropriate photophysical attributes. In comparison to the reference HTM (CJ06), the acceptor-integrated HTMs have exhibited potentially higher hole mobility rate, accredited to smaller hole reorganization energies (0.15 eV to 0.21 eV), greater transfer integral values (0.26 eV to 0.31 eV) and greater hole hopping rates (1.08×1028 S−1 to 3.70×1028 S−1). The electron-excitation investigation exhibited stronger electronic coupling, smaller hole-electron spatial overlapping, and higher charge transference length (19.42 Å to 21.14 Å) in the fabricated HTMs. Thus ensued a significant upsurge in intrinsic charge transference (74.22–99.74 %) and lower exciton binding energies, leading to easy charge dissociation and low recombination chances compared to the parent HTM (CJ06C1). Moreover, the findings from dipole moments (12.56 D to 13.05 D) and solvation-free energy (-91.08 kJ/mol) to −108.1 kJ/mol),imply easier processability and aptness for film formation. Overall, this study ensures the efficiency of thienodioxine core functionalization with acceptor moieties for fabricating state-of-the-art HTMs. The promising attributes of fabricated HTMs pave the way for forthcoming perovskite solar cells.

Computational Investigation of Structural, Electronic and Optical Properties of Ternary Chalcogenide TLGaQ2 Monoclinic Compounds: a First Principle Study

Purpose: This paper aim to investigate and predict by simulation the impact of the substitution of Q-site atom (Q꞊S, Se) on the TIGaQ2 monoclinic compounds for the first time, along the three main polarizations of the incident wave directions [100], [010] and [001]. Theoretical Framework: This study focuses mainly on ternary chalcogenide compounds TlGaQ2 (Q= S, Se) from ABQ2 family to highlight the objective resources aimed at promising prospects offered for them. Design/Methodology/Approach: A series of ab-initio calculations based on the (PW+PP) method within the density functional theory DFT framework were carried out with CASTEP code for the simulation of their physical properties (structural, electronic-optical). The exchange correlation potential was treated within the generalized gradient approximation (GGA) implemented in the CASTEP code and expressed by the PBE functional. Findings: The equilibrium lattice parameters are in good agreement with the available experimental results. The calculated band structure shows that are direct bandgap semiconductor nature 1.92eV (1.41eV) for TlGaS2 and TlGaSe2 respectively with a great potential for photovoltaic solar cell absorber materials. A set of optical parameters were calculated including the complex dielectric function, the reflective index, reflectivity, the absorption coefficient and loss function. The optical properties obtained revealed very interesting optical properties exhibiting strong optical absorption in UV range up to (~2x105cm-1) for both compounds making them appropriate for photovoltaic solar-cell absorber materials. Furthermore, low reflectivity and energy loss function are shown within in the visible and ultraviolet energy range, allowing them to be promising materials in several optoelectronics applications likes photosensitive devices. Implications: All these findings results show a successful accurately prediction for chalcogenide materials behavior and will be helpful for future studies allowing a better understanding of their potential applications in modern photovoltaic technologies as well as within UV ranges for optoelectronics applications.

Achieving Inkjet‐Printed 2D Tin Iodide Perovskites: Excitonic and Electro‐Optical Properties

AbstractCurrently, there is a great demand for non‐toxic lead‐free halide perovskites as active materials for solar cells, light‐emitting diodes and other optoelectronic devices. Although an essential progress has been made using tin(II) halide perovskites, still greater efforts are needed to improve their stability and manufacture films and devices under a scalable technology. The first goal of the work is to achieve suitable physical properties of 2D Sn(II) polycrystalline perovskite films obtained by the industrially scalable inkjet printing deposition technique. In the present work, inks of 2D tin(II) halide perovskite 2‐thiopheneethylammonium tin(II) iodide, TEA2SnI4, have been successfully formulated in DMF (toxic) and DMSO (non‐toxic) solutions and using appropriate additives (SnF2 and reducing agents) for improving the stability of the inks and the resulting films. Room‐ and low‐temperature excitonic photoluminescence (PL), charge carrier recombination dynamics and µ‐PL is used to explain the observed two excitonic bands, which are associated to the bulk and edges of perovskite grains nanoplatelet‐like composing the polycrystalline films. Promising electro‐optical properties are also obtained in the TEA2SnI4 films inkjet‐printed from DMSO formulations onto ITO‐interdigitated electrodes, such as low dark currents, ≈10 – 20 nA at 10 V of bias voltage, and high responsivities ≈1–20 A/W.

Multifunctional Modification of the Buried Interface in Mixed Tin-Lead Perovskite Solar Cells.

Mixed tin-lead perovskite solar cells can reach bandgaps as low as 1.2eV, offering high theoretical efficiency and serving as base materials for all-perovskite tandem solar cells. However, instability and high defect densitiesat the interfaces, particularly the buried surface,have limited performance improvements. In this work, we present the modification of the bottom perovskite interface with multifunctional hydroxylamine salts. These salts can effectively coordinate the different perovskite components, having critical influences in regulating the crystallization process and passivating defects of varying nature. The surface modification reduced traps at the interface and prevented the formation of excessive lead iodide, enhancing the quality of the films. The modified devices presented fill factors reaching 81% and efficiencies of up to 23.8%. The unencapsulated modified devices maintained over 95% of their initial efficiency after 2000 h of shelf storage.

Configurational design of NiPc derivative as electron transport material for stable and efficient perovskite solar cell: DFT and SCAPS-1D framework

In the present work electron transport layer is optimized to achieve the high stability and efficiency of Formamidinium tin iodide (FASnl3) perovskite solar cells (PSCs). Optical and electronic characteristics of designed ETLs were investigated by implying density functional theory. The designed ETLs show improved charge mobility over the nickel phthalocyanines (NiPcs). It has been observed that NiPc, a material for a hole-hole-transporting layer, acts as an electron transport layer in a modified configuration implying electron-withdrawing groups on the hydrogen site. In this study, the electron-withdrawing group (F−, Cl−, Br−, and I−) were substituted in the configuration X8Y8 (X and y are halide ions where X ≠ Y). Among various configurations, F8Br8NiPc demonstrates the maximum charge mobility 50 cm2/Vs Furthermore, the designed ETLs show improved stability over the NiPcs, due to their hydrophobic nature. Optimal characteristics for both the HTL and ETL were achieved to ensure enhanced efficiency. Furthermore, to investigate the impact of various parameters such as thickness, doping density, and defect density of the ETL layer SCAPS-1D numerical simulation was employed. The obtained electron affinity for designed HTL and ETL were found to be 2.4 eV and 4.247 eV respectively. The optimized photovoltaic (PV) characteristics including power conversion efficiency, short-circuit current density (Jsc), and open-circuit voltage (Voc) were found as 30.58 mA/cm2, 1.09 V, and 29.12 % respectively.

Semiconductor heterojunctions coated with reduced graphite oxide as electron transfer materials for high-performance perovskite solar cells

Exploring and insight into the relationship between the microstructure, light absorption performance, and carrier transport of perovskite light absorption layer materials and carrier transport layer materials is crucial for obtaining efficient and stable perovskite solar cells. We adopted a simple strategy to prepare a composite material known as reduced graphene oxide wrapped mesoporous hierarchical TiO2–CdS semiconductor heterojunctions (TiO2–CdS-RGO) as the electron transport layer in formamidine lead iodide perovskite solar cells. Compared with single TiO2 and binary composite, this composite material exhibits enhanced photoluminescence quenching, reduced photo generated carrier recombination rate, and improved electron transfer capability. Photovoltaic devices based on TiO2–CdS-RGO composite material showed a 14.5 % increase in short-circuit current density (JSC) and a 36.3 % increase in photoelectric conversion efficiency (PCE) compared to those with only TiO2. The improved optoelectronic properties observed with the TiO2–CdS-RGO as electron transfer layers can be attributed to several factors. On the one hand, mesoporous TiO2 with a high specific surface area is beneficial for perovskite infiltration and enhances electron transfer rate. On the other hand, the well-matching energy level structure among the three components aids in electrons extraction and reduces the recombination rate of photo generated charge carriers; In addition, RGO nanosheets with high conductivity serve as an efficient electron transfer network, providing a rapid charge transfer pathways, which is crucial for enhancing the photoelectric conversion performance of perovskite solar cells.

Constructions of NiCo2S4@rGO composite for use as a low-cost counter electrode material in dye-sensitised solar cells

Constructions of NiCo2S4@rGO composite for use as a low-cost counter electrode material in dye-sensitised solar cells

New hole transport materials based on polybenzo[1,2-b:4,5-b']dithiophene polymers with different side chains for n-i-p perovskite solar cells

A series of new homo- and copolymers P1–P6 with the main chains comprised exclusively of benzo [1,2-b:4,5-b']dithiophene units were synthesized using Stille polycondensation reaction. The optical and electrochemical properties of P1–P6 polymers were studied to estimate the frontier orbitals energies and the Eg values. The obtained data demonstrate the possibility of controlling the electronic properties of polybenzo [1,2-b:4,5-b']dithiophenes by varying only the structure and combinations of solubilizing alkyl side chains. The polymers P1–P6 were evaluated as hole transport materials in n-i-p perovskite solar cells. The highest efficiency of 18.6 % was delivered by the cells with one of the designed polymers with an optimal combination of alternating mono- and dialkylthiophene substituents. The high photovoltaic performance and decent operational stability were achieved using polymer films without any doping, which paves a way to design of inexpensive and scalable dopant-free materials for perovskite solar cells.

Enhanced Performance of Polymer Solar Cells by Ultraviolet-Ozone Treatment of MoOX Films with non-Thermal Annealing Treatment of MoOX Films

Molybdenum oxide (MoOX) is a commonly used hole extraction material (HEL) in polymer solar cells (PSCs). Here, we perform ultraviolet ozone treatment (UVO, non-thermal annealing treatment) on MoOX film (by spin-coated (NH4)6Mo7O24-4H2O solution on the ITO top) prepared by solution processing to develop hole extraction materials for efficient PSC. After UVO treatment of MoOX films (US-MoOX), the (NH4)6Mo7O24-4H2O molecules decompose to form a denser and higher energy levels MoOX film. Compared with E-MoOX films (vacuum evaporated MoO3 powder), US-MoOX films have similar square resistance and electrical conductivity to E-MoOX films, and the photovoltaic performance of US-MoOX-based PSCs is comparable to that of E-MoOX-based PSCs and higher than that of PEDOT:PSS-based PSCs. Therefore, US-MoOX-based PSCs show the advantages of combining high photovoltaic performance with solution processing. In addition, US-MoOX-based PSCs have the advantage of not requiring thermal annealing treatment. The results indicate that US-MoOX films are promising HEL materials for the practical production of PSCs.