Average Power Conversion Efficiency Research Articles

Recycling the Energy of Indoor Light: Highly Efficient Organic Photovoltaics via a Ternary Strategy

A ternary approach in organic photovoltaics (OPVs) is simple and reliable to effectively tune the optical, electrical, and morphological properties of the photoactive layer for high efficiency as well as long-term stability under 1 sun. However, there have been few papers reporting the benefits of ternary systems for recycling the energy of indoor light, which has narrow emission spectra and weak illumination compared to outdoor light. In this study, by using two compatible donor polymers (PM7 and PM7 D1) with slightly different band gaps and similar chemical structures, we demonstrate a simultaneous modulation of light absorption and molecular packing under ambient conditions, which resulted in efficient indoor OPVs exhibiting power conversion efficiency (PCE) over 20% under 1000 lx of warm white light-emitting diode (2900 K). From morphological analysis, we infer that PM7 serves to seed the nucleation of PM7 D1 in the ternary blend, templating its crystallization and alignment along the PM7 backbone. Such templating effect leads to increased domain spacing and relative degree of crystallinity (rDoC) compared to those of each binary system. We further show that higher rDoC helps suppress both bimolecular and trap-assisted recombination of photogenerated charges in the ternary devices. As a result, the complementary absorption and synergistic molecular assembly of the two donor polymers enhance the short-circuit current density as to increase the average PCEs from 9.6 to 10.3% under 1 sun and from 18.7 to 20.0% under 1000 lx. We envision that our strategy of incorporating both a planar and a flexible donor polymer with similar chemical structures can be generally applicable to attain a high-performance ternary OPV under both 1 sun and indoor light.

New Ternary Blend Strategy Based on a Vertically Self-Assembled Passivation Layer Enabling Efficient and Photostable Inverted Organic Solar Cells.

Herein, a new ternary strategy to fabricate efficient and photostable inverted organic photovoltaics (OPVs) is introduced by combining a bulk heterojunction (BHJ) blend and a fullerene self-assembled monolayer (C60 -SAM). Time-of-flight secondary-ion mass spectrometry - analysis reveals that the ternary blend is vertically phase separated with the C60 -SAM at the bottom and the BHJ on top. The average power conversion efficiency - of OPVs based on the ternary system is improved from 14.9% to 15.6% by C60 -SAM addition, mostly due to increased current density (Jsc ) and fill factor -. It is found that the C60 -SAM encourages the BHJ to make more face-on molecular orientation because grazing incidence wide-angle X-ray scattering - data show an increased face-on/edge-on orientation ratio in the ternary blend. Light-intensity dependent Jsc data and charge carrier lifetime analysis indicate suppressed bimolecular recombination and a longer charge carrier lifetime in the ternary system, resulting in the enhancement of OPV performance. Moreover, it is demonstrated that device photostability in the ternary blend is enhanced due to the vertically self-assembled C60 -SAM that successfully passivates the ZnO surface and protects BHJ layer from the UV-induced photocatalytic reactions of the ZnO. These results suggest a new perspective to improve both performance and photostability of OPVs using a facial ternary method.

Solution processable polypyrrole nanotubes as an alternative hole transporting material in perovskite solar cells

The major challenge towards the commercialization of perovskite solar cells is to find an alternative stable, low-cost, and solution-processible hole transporting material to unstable and expensive 2,2’,7,7’-tetrakis-(N,N-di-p-methoxyphenylamine)− 9,9’- spirobifluorene. Despite having all prerequisite properties like the ease of synthesis, low cost, tunability of hole conductivity, the conducting polymers such as polypyrrole are hardly being explored extensively as hole-transporting materials because of their insolubility in common organic solvents. Here, a colloidal solution of hydrophobic polypyrrole nanotubes co-doped with sodium dodecylbenzenesulfonate has been developed and explored for the hole transporting layer in methylammonium lead iodide-based perovskite solar cells. The best device has shown a power conversion efficiency of 7.3% at ambient conditions and without sealing. In terms of stability, the unsealed polypyrrole-based devices maintaining 85% of the initial efficiency at relative humidity 75–80 % with over 120 h have outperformed the unencapsulated poly(3-hexylthiophene)- based devices (average power conversion efficiency ∼11 %) fabricated using the same procedure and measured under same conditions. Frequency response analysis and electroluminescent imaging reveal that the photovoltaic performance of the polypyrrole-based cells can further be improved by reducing series resistance arising due to hole transporting layers. These studies show the polypyrrole colloids as a promising low-cost solution for the hole transporting layer in perovskite solar cells.

The effects of grating anatase on the photovoltaic performance of perovskite based solar cells

Stimulated by the extraordinary power conversion efficiency (PCE) of hybrid organic-inorganic perovskites (HOIP) based solar cells (SCs), the derivative studies on inorganic perovskites (IOP) based SCs have been intensely investigated. In order to overcome the disadvantages of CsPbBr3, most prominently the unfavorable larger band gap (2.3eV), a grating layer of mesoporous anatase TiO2(mp-TiO2) has been inserted into the conventional configuration of SCs. The grating layer acts as the electron transfer layer (ETL) and light absorption strengthening layer at the same time. Due to the combined effects, the increased contacting area increased the fill factor (FF) and enhanced light trapping in the grating layer increased the short-current density, the average PCE of IOP based SCs has increased from 5.67% to 7.58%, which is a ca. 34% increase relatively. Furthermore, research on traditional HOIP-based SCs is also conducted. Interestingly, the increasing PCE mechanism is quite different from their inorganic counterparts, which should be attributed to the strain effect of different film structures. Thus, the strain-induced defect charge-state transitions of MAPbI3 by the grating layer increased the open-circuit voltage (Voc); and similarly, the increased contacting area also increased the FF, resulting in a 13% increase for PCE.

A promising scalable bar coating approach using a single crystal-derived precursor ink for high-performance large-area perovskite solar cells

Perovskite solar cells (PSCs), with demonstrated high efficiencies in a lab scale, are regarded as potential energy-harvesting materials if the challenges like large-area manufacturing and long-term stability are achieved. In an effort to fabricate PSCs on large-area substrates, the study herein reports the use of an economic and scalable bar coating method for the fabrication of PSCs. Bar coating is used initially to coat electron transport layers on large-area (50 mm × 50 mm) FTO glass substrates. A methyl ammonium lead iodide (MAPbI3) perovskite absorber has been bar coated on the electron transport layers coated FTO glass substrates using a single-crystal-derived perovskite precursor. The single crystal-derived precursor has resulted in large-area uniform perovskite absorbers and, thus, characterized appositely to establish the uniform coverage of desired quality MAPbI3. The spatial distribution of photoluminescence and absorption spectra of the perovskite absorber, collected systematically, confirms the device quality MAPbI3, with identical characteristics ascertaining the homogeneity of perovskite coating. Solar cells fabricated using bar-coated large-area perovskite absorbers have exhibited a champion power conversion efficiency of 15.6%, with the average power conversion efficiency being 14.5%, unveiling an excellent performance homogeneity. Further, the champion devices of bar-coated PSCs are compared with control devices fabricated by spin coating of a powder-derived precursor. Bar-coated PSCs have not only exhibited significantly higher performance but also showed comparable reproducibility and much lower hysteresis values than the control PSCs, demonstrating the efficacy of the bar coating method towards fabricating large-area PSCs.

Ultra-thin thermally grown silicon dioxide nanomembrane for waterproof perovskite solar cells

Recently, perovskite solar cells (PSCs) have been attracting attention as the most promising alternative to conventional photovoltaics, mainly due to their high power conversion efficiency (PCE) of 25.7%. However, prior to commercialization, problems with their long-term stability caused by moisture should be solved. Accordingly, encapsulation is a crucial strategy for enhancing the long-term stability of PSCs, meaning a well-established strategy that includes an excellent barrier that protects them from the external environment while minimizing any damage during encapsulation is required. In this study, a room temperature thin-film encapsulation (RT-TFE) strategy is applied by transferring a defect-free thermally grown silicon dioxide nanomembrane (t-SiO2 NM), which is a well-known superior water molecule barrier, onto the PSCs. The average PCE of the devices decreased by only 0.012% with a standard deviation of 0.4249 during the entire encapsulation process, which was achieved by minimizing any thermal degradation of the photovoltaic components, including the perovskite and hole transport layers. This t-SiO2 NM successfully protected the PSC from external water molecules in an underwater condition for 31 days at room temperature, which is the longest reported survival time of encapsulated PSCs. As a result, the RT-TFE PSC maintained more than 98% of the initial efficiency.

Surface Modification of NiOx Layer with Versatile Coupling Agent Enables Enhanced Performance and Stability of Inverted Perovskite Solar Cells

In recent years, nickel oxide (NiOx) is widely used as an excellent hole transport layer for the inverted perovskite solar cells (PSCs), due to its decent hole conductivity, easy processability, and low cost. However, the photovoltaic performance and stability of NiOx‐based PSCs are severely limited by the poor perovskite/NiOx interface. Herein, a versatile coupling agent di(dioctylpyrophosphato) ethylene titanate (NDZ‐311) is introduced to improve the performance of NiOx‐based inverted PSCs by suppressing nonradiative recombination and strengthening charge transfer at the perovskite/NiOx interface. Moreover, the chemical reaction between NDZ‐311 and NiOx reduces the surface hydroxyl groups of NiOx film and avoids direct contact between perovskite and NiOx film, which mitigate material degradation caused by high‐valence Ni ions and hydroxyl groups. As a result, the average power conversion efficiency (PCE) of inverted PSCs is enhanced from ≈18.01% to ≈19.92% and a maximum PCE of ≈20.39% is obtained. The unencapsulated PSC with NDZ‐311 modification maintains 87.65% of their initial performance after 400 h aging test in air, much better than the control device (49.41% after 400 h). The work demonstrates the potential application of NDZ‐311 for commercial PSCs, considering NDZ‐311 is a cheap industrial material.

Efficiency enhancement of copper indium gallium selenide solar cells fabricated on polyimide foils with multiple metal layers

In this work, we report the fabrication method using a Cu(In,Ga)Se2 (CIGS) quaternary target containing NaF to obtain thin-film solar-cell devices on polyimide (PI) foils. In order to improve the efficiency of the CIGS solar cells, multiple metal layers were prepared on both sides of the PI substrate, and the annealing process was investigated. The sandwich structure of Ti/Cr/Mo multiple layers prepared on PI foils can improve thermal budget of the substrate as it endures higher annealing temperature (520 °C) for short time (5 min). A 2-step annealing process was adopted to ensure the integrity and fewer electrical defects of the absorber film. The distribution of Na and Ga elements in the annealed films was improved by adding a high-temperature selenization process. CIGS cells with better conversion efficiency can be obtained by this fabrication process. An average power conversion efficiency of 13.6% has been achieved for the prepared cells.

Environmentally friendly cathode interlayer modification on edible bio‐acids with enhanced electron extraction and improved power conversion efficiency

AbstractRealizing environmental compatibility and high power conversion efficiency (PCE) are crucial in the research of organic photovoltaics towards practical application. Applying environmentally friendly bio‐materials into the modification of cathode interlayer (CIL) is a feasible approach to move towards both targets. In this research, three edible bio‐acids, ursolic acid, citric acid, and malic acid, are employed to modify the PDIN CIL of the organic solar cells (OSCs) with non‐fullerene acceptors. Among these edible bio‐acid modifiers, ursolic acid shows its excellent performance in improving interfacial contact and suppressing charge recombination. It helps to obtain a good interfacial contact and facilitates the electron extraction. As a result, the photovoltaic performance is significantly improved. The average PCE are increased from 17.58% of the control devices to 18.35% of the PDIN + Ursolic Acid based devices, with a maximum PCE of 18.54%. It is the champion efficiency among the reported applications of bio‐derived materials for the CILs. This study demonstrates the successful application of edible bio‐acid, which offers an effective and green approach for the CIL modification to realize highly efficient OSCs.image

Analysis of a novel method of alkalis treatment: Effect on energy band optimization and carrier recombination at the grain boundary

Alkali metal post-deposition treatment (PDT) is a key factor to approach high efficiency in Cu(In, Ga)Se 2 (CIGS) solar cells. In addition to single alkali element treatment, co-doping of light and heavy alkali elements is also applied to the preparation of CIGS absorber for higher efficiency. In this work, the details of different methods of alkali-treatments are revealed by combining several microstructural and compositional analysis methods, especially for the NaF-PDT/CsF-PDT process which introduces extra Na before Cs into the absorber. The ion exchange of Na and Cs in the grain boundaries (GB) of the absorber is analyzed in detail, which reveals alkali-treatment restrains the formation of large bandgap compounds at GB. Extensive material analysis shows that NaF/CsF-PDT can not only tailor the surface nanoscale morphology of CIGS films but also optimize the band structure at GB to reduce carrier recombination. Such modification gains the improvement of the highest power conversion efficiency (PCE) from 15.2% to 17.4% and average PCE from 14.3% to 16.5% (without antireflective coating) after NaF/CsF-PDT. According to the analysis of data, we propose a model of energy band at GB, which explains the reason why NaF/CsF-PDT shows a better effect on CIGS devices than CsF-PDT. These results could serve as a basis for the further understanding of the effects of alkali-PDT on CIGS film and help to achieve even higher efficiency. • Effects of alkali elements Na and Cs on CIGS solar cells are investigated by a series of characterization tools. • NaF/CsF-PDT can tailor the surface nanoscale morphology and optimize the band structure at CIGS films. • An energy band model of GBs is proposed to explain the effect of alkali metal co-doping. • The PCE improved from 15.2% to 17.4% after NaF/CsF-PDT.

Electrochemical deposition of NiO bunsenite nanostructures with different morphologies as the hole transport layer in polymer solar cells

• Electrodeposition of p-type nickel oxide (NiO) using anodic potentiostatic and cyclic voltammetry. • Applying both NiO as the hole transport layer (HTL) in the fabrication of polymer solar cells. • NiO synthesized by the anodic potentiostatic exhibited the best features as the HTL. • The best PSC showed J SC , V OC , FF , and PCE of 10.95 mA/cm 2 , 0.64 V, 0.60 and 4.21%, respectively. Hole transport layers (HTLs) are one of the most important components of bulk heterojunction polymer solar cells (BHJ PSCs), having functions of optimizing interface, adjusting the energy match, and helping obtain higher PCE. Inorganic p-type semiconductors are alternative HTLs due to their chemical stability, high mobility, high transparency, and applicable valence band (VB) energy level. In this work, interlayer engineering in BHJ PSC was performed using solution-processed p-type nickel oxide (NiO) as the HTL. NiO nanostructures were synthesized by anodic potentiostatic and cyclic voltammetry (CV) electrodeposition methods. Simple adjustment of the applied potential regime and electrodeposition parameters led to considerable structural and electrochemical changes in the resulting NiO. Eventually, the best sample was selected in terms of suitable surface conductivity, high optical transparency, and appropriate energy levels. NiO nanostructures with FCC crystal structure synthesized by anodic potentiostatic electrodeposition showed conductivity of 0.038 mS.cm -1 and charge mobility of 2.01 cm 2 .V -1 s -1 , respectively, about 30.2% and 24.8% higher than the NiO synthesized by CV. The anodic potentiostatic electrodeposition method increased the photovoltaic performance of the PSCs by 43% compared to the CV method. The average power conversion efficiencies for the anodic potentiostatic and CV methods were 2.95% and 4.21%, respectively. The PCE of these cells was about 13% and 62% higher than that considered for the reference device prepared based on the PEDOT:PSS HTL.

Dual-Functional 3-Acetyl-2,5-dimethylthiophene Additive-Assisted Crystallization Control and Trap State Passivation for High-Performance Perovskite Solar Cells

Defect-mediated charge recombination and successive degradation mainly lag the performance of perovskite solar cells (PSCs). Insufficiency or evaporation of organic cations leaves behind the undercoordinated Pb2+ ions, which act as severe charge recombination centers. Herein, theoretical and experimental insights into crystallization control and defect passivation of MAPbI3 perovskite by the dual-functional 3-acetyl-2,5-dimethylthiophene (ADT) molecule are presented. Density functional theory calculations show that both functional groups of ADT possessing different interaction energies could interact with PbI2. The carbonyl group in ADT shows the dominant interaction with Pb2+ forming an intermediate product that might decrease the crystallization rate. Further, the coordinate bonding between ADT and uncoordinated Pb2+ ions in perovskite leads to defect passivation. The 0.6% ADT-modified PSCs possess an average power conversion efficiency (PCE) of 18.22 ± 0.80% and the highest PCE of 19.03%, whereas the pristine PSCs exhibit an average PCE of 16.23 ± 1.32% and the highest PCE of 17.47%. Furthermore, the modified PSCs maintain 80% of the initial PCE up to 650 h during storage at ambient conditions (RH = 35 ± 5%). The present study shows that the simultaneous crystalization control and defect passivation achieved via an ADT additive engineering approach could be an efficient strategy to enhance the PCE and stability of PSCs.

Ecofriendly Hydroxyalkyl Cellulose Additives for Efficient and Stable MAPbI3‐Based Inverted Perovskite Solar Cells

Perovskite solar cells (PSCs) have been demonstrated to be one of the most promising technologies in the field of renewable energy. However, the presence of the defects in the perovskite films greatly limits the efficiency and the stability of the PSCs. The additive engineering is one of the most effective approaches to overcome this problem. Most of the successful additives are extracted from the petroleum‐based materials, while the research on the biomass‐based additives is still lagging behind. In this paper, two ecofriendly hydroxyalkyl cellulose additives, i.e., hydroxyethyl cellulose (HEC) and hydroxylpropyl cellulose (HPC), are investigated on the performance of the MAPbI3‐based inverted PSCs. Due to the strong interaction between the hydroxyl groups of the cellulose and the divalent cations of the perovskite, these additives enhance the crystal grain orientation and significantly repair the defects of the perovskite films. Working as the additives, these two cellulose derivatives show a strong passivation ability, which significantly reduces the trap density and improves the optoelectronic feature of the PSCs. Compared with the average power conversion efficiency (PCE) of the control device (19.19%), an enhancement of ~10% is achieved after the addition of HEC. The optimized device (PCE = 21.25%) with a long‐term stability (10:80 h, PCE = 20.93%) is achieved by the incorporation of the HEC additives into the precursor solution. It is the best performance among the PSCs with the cellulose additives up to now. This research provides a novel choice to develop a cost‐effective and renewable additive for the PSCs with high efficiency and excellent long‐term stability.

Orotic Acid as a Bifunctional Additive for Regulating Crystallization and Passivating Defects toward High-Performance Formamidinium-Cesium Perovskite Solar Cells.

Formamidinium-cesium (FA-Cs) perovskites are an attractive candidate for perovskite solar cells (PSCs) with high stability, but they tend to suffer from high intrinsic defect density, especially at grain boundaries. Herein, a common heterocyclic conjugated molecule, orotic acid (ORO), was employed as a novel bifunctional additive to simultaneously achieve crystallization regulation and defect passivation of an FA-Cs perovskite toward efficient and stable PSCs. ORO was introduced to an FA-Cs perovskite precursor solution as an effective coordination-induced crystallization regulator to improve the grain size and crystallinity. Furthermore, under the assistance of π electrons, its carboxyl group bonded with undercoordinated Pb2+ defects at grain boundaries, and it was also able to form hydrogen bonds with undercoordinated I- defects, thus significantly reducing defect density. The average power conversion efficiency of the produced PSC devices with the ORO additive was promoted from 17.81% for the control PSCs to 19.32%, and a champion efficiency of 20.62% with negligible hysteresis was achieved. Additionally, the optimized devices exhibited high resistance to moisture incursion, leading to decent environmental stability. This work provides a convenient yet efficient approach to improve crystallization and passivate defects toward PSCs with enhanced efficiency and stability.

Achieving highly efficient and stable MAPbI3 planar solar cell by embedding Cs+, Fe2+, and Cd2+ metal inorganic cations in perovskite structure

Perovskite solar cells (PSCs) have been attracted the attention of many researchers due to their high conversion efficiency, low manufacturing cost, easy manufacturing steps, high light absorption, and the possibility of changing the photo electronic properties by modifying the chemical structure. Despite the mentioned advantages, the low stability of PSCs and toxicity of lead in the perovskite layer were the challenging issues in this field. In this regard, the use of mixed cation and mixed halide perovskite compounds with high crystal quality, efficiency, and stability has attracted enormous attention. In this project, Fe2+, Cd2+, and Cs+ cations with various contents (Fe2+ + Cd2+: 5% and 10%; Cs+: 5% and 10%) were partially replaced the Pb2+ and CH3NH3+ cations, respectively in the MAPbI3 perovskite structure through a two-step process using spin-coating. The as-synthesized [CsyMA1-yPb1-a-bFeaCdbI3-2aCl2a], (a+b): 5, 10%, y: 5, 10%) perovskites were characterized with X-ray diffraction (XRD), grazing incidence X-ray diffraction (GIXRD), and field emission scanning electron microscopy (FESEM). The optical properties of prepared compounds were investigated by ultraviolet–visible (UV–Vis) and photoluminescence (PL) spectroscopy. The photovoltaic behavior as well as stability of solar cells containing MAPbI3, [CsyMA1-yPb1-a-bFeaCdbI3-2aCl2a], (a+b): 5%, y: 5%), and [CsyMA1-yPb1-a-bFeaCdbI3-2aCl2a], (a+b): 10%, y: 10%) perovskites as active layers were evaluated by current density-voltage (I–V) under AM1.5G illumination.Results showed that partial substitution of CH3NH3+ cations with Cs+ and Pb2+ cations with Fe2+ + Cd2+ in the CH3NH3PbI3 structure improved crystallinity and photovoltaic parameters. The average power conversion efficiency (PCE) of six solar cell containing [CsyMA1-yPb1-a-bFeaCdbI3-2aCl2a], (a+b): 10%, y: 10%) perovskite layer was 21.04% which was 1.03 and 1.21 times higher than that cells containing [CsyMA1-yPb1-a-bFeaCdbI3-2aCl2a], (a+b): 5%, y: 5%) and MAPbI3, respectively.The electrochemical impedance spectroscopy (EIS) was utilized to study the charge transfer resistance (Rct) and recombination resistance (Rrec) of prepared solar cells. The Rct and Rrec values of fabricated solar cell were decreased and increased, respectively in the presence of Fe2+, Cd2+, and Cs+ inorganic cations. As a result, the [CsyMA1-yPb1-a-bFeaCdbI3-2aCl2a] perovskites can be considered as the appropriate candidate with high efficiency, stability, and low lead content in the planar perovskite solar cells.

Precisely preparing lead iodide passivation layer for enhancing the performance of triple cation perovskite solar cells using krypton fluoride excimer laser

Precisely controlling the amount and location of PbI2 in a lead halide perovskite light absorption layer is crucial for improving the performance of perovskite solar cells (PSCs) by utilizing the passivation effect of PbI2. Based on the high absorption coefficient of perovskite materials and the resulting extremely shallow UV penetration depth, a non-contact approach of the precise preparation of a PbI2 passivation layer based on excimer laser irradiation (ELI) is proposed. 248 nm KrF excimer laser is adopted to irradiate the surface of [(FAPbI3)0.87(MAPbBr3)0.13]0.92[CsPbI3]0.08 film, and a PbI2 passivation layer could be obtained on the surface of the triple cation perovskite film through the partial decomposition of the surface layer of perovskite films induced by ELI process. And then, the average power conversion efficiency of the PSCs has been increased obviously from 17.82% to 20.68%. This non-contact photonic approach successfully breaks through the bottleneck of precisely preparing PbI2 passivation layer and is expected to contribute to the further development of perovskite based devices.

Immobilised TiO2 Mesocrystals with Exposed {001} Facets for Efficient Dye‐Sensitized Solar Cells

The immobilization of titanium dioxide is necessary for several energy and environmental applications such as dye‐sensitized solar cells (DSSCs). A two‐step fabrication route has been developed in this work including a near room temperature hydrolysis reaction to produce immobilized (NH4)2TiOF4 arrays, followed by successive topotactic transformations to immobilised TiO2 mesocrystals (imcTiO2). Hierarchical mesocrystal structure has thereby been successfully introduced to immobilised TiO2 without the use of expensive equipment or complex strategies. Thanks to the features of the nano‐building blocks such as high surface area and high active {001} facets; collective properties including the common orientation of nanoparticles; and strong adhesion to the substrate inherited from the immobilized (NH4)2TiOF4 precursor, the imcTiO2 possesses a high dye pickup capability and optimal electron transport ability. The average power conversion efficiency from imcTiO2 based DSSCs is comparable to devices with two layers of printed commercial TiO2 under the same sintering condition, with the balanced short circuit current densities, similar open‐circuit voltages, and outstanding fill factors.

Ti3C2Tx-Modified PEDOT:PSS Hole-Transport Layer for Inverted Perovskite Solar Cells.

PSS is a commonly used hole-transport layer (HTL) in inverted perovskite solar cells (PSCs) due to its compatibility with low-temperature solution processing. However, it possesses lower conductivity than other conductive polymers and metal oxides, along with surface defects, limiting its photovoltaic performance. In this study, we introduced two-dimensional Ti3C2Tx (MXene) as an additive in the PEDOT:PSS HTL with varying doping concentrations (i.e., 0, 0.03, 0.05, and 0.1 wt.%) to tune the electrical conductivity of PEDOT:PSS and to modify the properties of the perovskite film atop it. We noted that the grain size of the CH3NH3PbI3 (MAPI3) perovskite layer grown over an optimal concentration of MXene (0.03 wt.%)-doped PEDOT:PSS increased from 250 nm to 400 nm, reducing charge recombination due to fewer grain boundaries. Ultraviolet photoelectron spectroscopy (UPS) revealed increased work function (WF) from 4.43 eV to 4.99 eV with 0.03 wt.% MXene doping, making the extraction of holes easier due to a more favorable energy level alignment with the perovskite. Quantum chemical investigations based on density functional theory (DFT) were conducted at the ωB97XD/6-311++G(d,p) level of theory to provide more insight into the stability, bonding nature, and optoelectronic properties of the PEDOT:PSS-MXene system. The theoretical investigations revealed that the doping of PEDOT:PSS with Ti3C2Tx could cause a significant effect on the electronic properties of the HTL, as experimentally demonstrated by an increase in the electrical conductivity. Finally, the inverted PSCs employing 0.03 wt.% MXene-doped PEDOT:PSS showed an average power conversion efficiency (PCE) of 15.1%, up from 12.5% for a reference PSC employing a pristine PEDOT:PSS HTL. The champion device with a 0.03 wt.% MXene-PEDOT:PSS HTL achieved 15.5% PCE.

Sputtering Al2O3 as an effective interface layer to improve open-circuit voltage and device performance of Sb2Se3 thin-film solar cells

Sb2Se3 as a promising photovoltaic absorber material is attracting increasing attention. However, high open-circuit voltage (VOC) loss, especially for superstrate structured Sb2Se3 solar cells, is one of the main bottlenecks for improving device efficiency. Here, sputtering aluminum oxide (Al2O3) as an interface layer between CdS and Sb2Se3 was applied in superstrate structured Sb2Se3 solar cells. We proved that the sputtered Al2O3 layer is not fully continuous on the rough CdS film even its thickness has reached 8.8 nm. Then we systematically investigated the influence of the Al2O3 layer on Sb2Se3 material properties and device performances. It is found that the Al2O3 layer can not only effectively inhibit [hk0]-oriented crystal growth and promote [hk1] growth orientation of Sb2Se3 films but also obviously weaken the disordered growth of prominent petal-like shape Sb2Se3 grains and reduce the surface roughness. Further, the Al2O3 layer can also availably passivate interfacial defects at the CdS/Sb2Se3 interface. Consequently, the average power conversion efficiency (PCE) of Sb2Se3 solar cells with an optimal Al2O3 layer thickness is 17.86% higher than that without the Al2O3 layer. Noteworthily, the VOC of Sb2Se3 solar cells is boosted to 0.462 V, which is the highest value in superstrate structured Sb2Se3 solar cells with absorber prepared by conventional physical methods. Finally, a champion efficiency of 6.25% has been achieved in a low-cost Sb2Se3 thin-film solar cell with FTO/CdS/Al2O3/Sb2Se3/Carbon device configuration.

Synergistic dual-interface modification strategy for highly reproducible and efficient PTAA-based inverted perovskite solar cells

Poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA)-based inverted perovskite solar cells (PSCs) are the most efficient device type reported to date. Nevertheless, the high hydrophobicity of PTAA and the nonradiative recombination loss significantly limit the repeatability and the performances of these devices. In this study, polyvinyl oxide (PEO) and tetra-n-propylammonium bromide (TPAB) were introduced to overcome the hydrophobicity of PTAA and the anode and cathode interface nonradiative recombination losses through the synergistic effect of these materials. The results showed that the PEO could dramatically improve the wetting properties of the perovskite precursor on the PTAA surface, correspondingly enhancing the microstructure of the film, eliminating the defects, and enhancing the anode interfacial contact of the device. The performances and performance repeatability of the devices were greatly improved. The ratio of the short-circuited devices decreased from 44.23 % to 0 %, and the average power conversion efficiency (PCE) increased dramatically. In addition, a facile TPAB surface treatment strategy was proposed to reduce the potential threat of PEO introduction to the device stability as well as improve the cathode interface contact problems of the device. Owing to the synergistic effect of the PEO and TPAB, the performance and stability were both enhanced. The highest PCE of 21.62 % was achieved, and the average PCE of TPAB devices could be maintained at 80 % for 298 h (in air, 23 °C, 25 RH%) and 96 % for 217 d (in N2, 23 °C) of the initial PCE value. The synergistic dual-interface modification strategy proposed in this paper lights the way for the preparation of highly reproducible, efficient, and stable PTAA-based inverted perovskite solar cells.