Original Power Conversion Efficiency Research Articles

Chemical polishing and sub-surface passivation of perovskite film towards high efficiency solar cells

Eliminating surface defects and impurities on metal halide perovskite (MHP) films through chemical reactions represents a novel strategy to improve the performance of perovskite solar cells (PSCs), which can be referred to as “chemical polishing”. This approach is anticipated to be more facile, precise, and distinct from the extensively documented surface passivation methods in terms of its underlying mechanism. However, to date, the underlying selective chemical reaction mechanism still requires in-depth study. In this context, we present a novel two-step chemical polishing method that eliminates surface impurities while simultaneously passivating the sub-surface. The core principle of this method involves two primary steps: (1) the creation of two-dimensional (2D) perovskite via selective reactions between polishing agents (n-octylammonium bromide, OABr) and undesired metastable amorphous species, as well as residual PbI2 nanocrystals present on the surface of MHP films. (2) Subsequently, the 2D perovskite and excess polishing agents are efficiently eliminated using a mixed solvent. Following the polishing process, the sub-surface, which is passivated by residual OABr, contains fewer defects and can establish improved electrical contact with the hole transport layer (HTL). As a result, the power conversion efficiency (PCE) of PSCs is enhanced from 21.7% to 23.6%. Moreover, the PSCs processed with chemical polishing exhibit enhanced long-term operational stability, with a capability to retain 80.2% of their original PCE value after 1500 h of illumination.

Polymer Poly (Ethylene Oxide) Additive for High-Stability All-Inorganic CsPbI3−xBrx Perovskite Solar Cells

All-inorganic CsPbI3−xBrx perovskite solar cells (PSCs) are becoming increasingly mature due to their excellent optoelectronic properties. However, because of the poor environmental stability of the perovskite material, the device is susceptibly decomposed when exposed to moisture, high temperature, and high illumination. Therefore, a critical task is to address the problem of poor long-term stability in the environment, which serves as a significant obstacle impeding the commercialization of perovskite solar cells. This article introduces the incorporation of PEO into all-inorganic CsPbI3−xBrx perovskites with an advantageous thermal stability. PEO acts as a passivating agent near the grain boundary, and its high viscosity characteristics effectively improve the film-forming properties, leading to a substantial reduction in defects and to improving the surface uniformity. In addition, the grain boundaries that serve as water and oxygen penetration channels are filled, resulting in a substantial improvement in device stability. With 7.5 mg/mL PEO doping into CsPbI3−xBrx, the unencapsulated device maintained its original power conversion efficiency of 98% after being placed in a dark environment of 40% humidity and 25 °C for 10 days. Using PEO effectively enhanced the performance of the devices, with the highest PCE reaching 10.95%, significantly improving environmental stability.

Additive Engineering of Imidazolium-based cation for defect passivation with enhanced performance and stability of carbon-based perovskite solar cells

Due to the rapid increase in the power conversion efficiency (PCE) of perovskite solar cells (PSCs) and approaching the theoretical maximum level in recent years, the main drawback of their future commercialization is to improve their long-term stability under existing environmental conditions. One of the problems with this technology lies in the absorbing layer, specifically the perovskite. In particular, when producing a perovskite film under ambient conditions, it is almost impossible to avoid film defects caused by environmental conditions (such as moisture, oxygen, and temperature), which could randomly change during the preparation process. Therefore, the fabrication of high-quality perovskite films is an urgent process that has a direct impact on the overall performance of the solar cells. The use of ionic liquids (ILs) as additives in perovskite precursor solutions is a promising strategy to improve not only the power conversion efficiency (PCE) but also the long-term stability of photovoltaic devices by controlling nucleation and crystal growth of perovskite film that avoids defects and produces high-quality perovskite layers. Here, the critical role of the ionic liquid 1-methyl-3-propylimidazolium iodide (1-MPII) in different perovskite precursor solutions such as MAPbI3 (I), MAPbI3-PbBr2 (B) and MAPbI3-PbCl2 (CL) on carbon-based perovskite solar cells (C–PSCs) under ambient conditions is extensively studied. The results show that 1-MPII ionic liquid activates the surface morphology of all perovskite films and improves solar cells’ efficiency due to the passivation of the uncoordinated Pb2+ defects. Furthermore, stability measurements show that the unencapsulated IL-modified devices for perovskites MAPbI3 (IIL), MAPbI3-PbBr2 (BIL), and MAPbI3-PbCl2 (CLIL) retained at 84 %, 86 %, and 80 % of their original PCE for over 1100 h under ambient conditions with 45 % relative humidity (RH), compared to the IL-free PSCs. Moreover, the IL-modified PSCs exhibited an increased electrical performance ranging from 16.5 % to 33 % depending on the type of perovskite it was used, so that long-term stability also was reinforced.

Surface defect passivation by copper incorporation for efficient perovskite solar cells

Defects play an important character in the degradation processes of hybrid halide perovskite, hindering their application for solar cells. Ion transport is facilitated by the ubiquitous organic cation and halide anion vacancy defects, which lead to perovskite disintegration at grain boundaries. In this article, a thorough investigation of the vacancy defect and defect density on perovskite is conducted by using VASP and SCAPS-1D. From SCAPS-1D, the PCE of the device increases from 17.82 % to 23.04 % when the defect state density drops from 10+15 to 10+14 cm-3. Therefore, reducing the defect density is very important to improve the performance of perovskite solar cells. Effective perovskite solar cells based on CH3NH3PbI3 incorporated copper ions passivation defects were carried out. Compare to pristine hybrid perovskite, Cu2+-doped hybrid perovskite have remarkably lower trap-state densities, greater film quality, and higher crystallinity. Especially, the maximum power conversion efficiency of up to 20.1 % was achieved with 0.5 % copper ion doping. After 500 h of not being enclosed in dry air, the devices still has 87 % of its original power conversion efficiency. Therefore, this work suggests that careful control the formation of Cu2+ in perovskite films is very important for diverse optoelectronic applications in the future.

Ligand‐Mediated Homojunction Structure for High‐Efficiency FAPbI3 Quantum Dot Solar Cells

AbstractFormamidinium lead iodide quantum dots (QDs) show great potential for solar cell applications but suffer from restricted charge transfer due to the insulating nature of their ligand shell. Management of the surface properties and resultant energy band alignment is the key to efficient and stable QD solar cells. Herein, an advance in QD surface passivation by introducing tailored multifunctional ligands (glycocyamine (GLA)) to the FAPbI3 QD surface is demonstrated. The incorporation of GLA ligands can partly substitute the native long‐chain insulating ligands and effectively reduce the non‐radiative recombination loss induced by surface trap states. Notably, the introduction of GLA ligands beneficially shifts the band offsets of the QD films and generates a homojunction structure with a cascading energy band alignment in the QD layers, promoting favorable charge transport and boosting the device's performance. As a result, a record‐high power conversion efficiency (PCE) of 15.34% with improved open‐circuit voltage and fill factor is achieved. Moreover, the GLA‐assisted surface passivation boosts the device stability, in which over 80% and 75% of the original PCEs are maintained after storing the devices for 5500 h in ambient air and 768 h under continuous 1‐sun illumination, respectively.

Synergistic Defect Passivation and Crystallization Modulation in Efficient Perovskite Solar Cells: The Case of Multifunctional 2-Anisidine-4-Sulfonic Acid.

With the continuous development of the performance of perovskite solar cells, the high-density defects on the perovskite film surface and grain boundaries as well as undesired perovskite crystallization are increasingly emerging as challenges to their commercial application. Herein, a dye intermediate 2-anisidine-4-sulfonic acid (2A4SA), containing sulfonic acid group (SO3-), amino group (-NH2), methoxy group (CH3O-), and benzene ring, which exhibit a synergistic effect in comprehensive defect passivation and crystallization modulation, is incorporated. Detailed investigations show that the SO3- of 2A4SA with high electronegativity firmly chelates with uncoordinated lead ions through the coordination interaction, while the -NH2 and the CH3O- of 2A4SA separately immobilize iodide ions and organic cations in the perovskite lattice through hydrogen bonds, enabling substantially decreased nonradiative recombination and trap state density. Meanwhile, 2A4SA molecules attached to the surface of perovskite nuclei can delay crystallization kinetics and promote preferred vertical growth orientation, thereby attaining the high-crystallinity and large-size-grain perovskite films. Consequently, the 2A4SA-doped device with the structure ITO/SnO2/Cs0.15FA0.75MA0.10PbI3 (2A4SA)/Spiro-OMeTAD/Ag presents a splendid power conversion efficiency (PCE) of 23.06% accompanied by increased open-circuit voltage (1.15 V) and fill factor (82.17%). Furthermore, the optimized film and device demonstrate enhanced long-term stability. The unencapsulated optimized device retains ≈80% of the original PCE after 1000 h upon exposure to ambient atmosphere (20-50% RH), whereas the control group is only 56.8%.

Porous Lead Iodide Layer Promotes Organic Amine Salt Diffusion to Achieve High Performance p‐i‐n Flexible Perovskite Solar Cells

AbstractFlexible perovskite solar cells (FPSCs) are attracting widespread research and attention for their benefits as the next‐generation wearable electronic products. However, there are still many challenges in the quest to achieve dense, pinhole‐free, high crystal quality, low defect, and stable perovskite films, which limit further improvement in the efficiency and stability of FPSCs. Herein, a novel technique for the incorporation of quaternary ammonium halide (QAH) additives to prepare fluffy porous lead iodide layers by using a two‐step sequential deposition method, is reported. Benefiting from the good diffusion of organic amine salts on porous PbI2 layers, flat and dense perovskite films are produced with large particle sizes, few defects, and high crystal quality. Finally, the champion rigid and flexible p‐i‐n PSCs with the 2‐(acetyloxy)‐N,N,N‐trimethylethanium chloride (AtaCl) additive achieves exciting power conversion efficiencies (PCE) of 23.40% and 21.10%, respectively. The device with the AtaCl additive retains over 90% of its original PCE under ambient conditions (40 ± 5% relative humidity (RH)) over 1000 h of aging without encapsulation. In addition, the flexible device with the AtaCl additive shows excellent stability under mechanical bending conditions, retaining ≈85% of its original PCE after 10 000 cycles (bending radius = 5 mm).

Enhanced flexibility and light utilization for high-efficiency all-air-processed carbon-based perovskite solar cells

The hole transport material (HTM)-free carbon-based perovskite solar cells (C-PSCs) are widely recognized as competitive candidates towards practical applications. However, the poor mechanical connection at perovskite/carbon interface and the low light transmittance of flexible substrates limit the fabrication of high-efficiency flexible HTM-free C-PSCs. In this paper, we develop flexible HTM-free C-PSCs with enhanced flexibility and light utilization by implanting carbon nanotubes (CNTs) into perovskite film and carbon electrode to boost the connection at perovskite/carbon interface as well as by coating a polymethyl methacrylate (PMMA) antireflection layer to enhance light utilization of the polyethylene naphthalate/indium tin oxide (PEN/ITO) substrates. The CNTs are proven to not only enhance the flexibility of the devices, but also facilitate charge extraction and transfer at perovskite/carbon interface. The average transmittance of the PEN/ITO substrates increase by 3.63% after the incorporation of PMMA antireflection layer. As a result, the flexible HTM-free C-PSC with an architecture of PMMA/PEN/ITO/SnO2/MAPbI3/carbon presents a power conversion efficiency (PCE) of 14.44%, which is the highest PCE for flexible HTM-free C-PSC devices. Moreover, this flexible PSC retains more than 84% of the original PCE after bending 1000 cycles at 7 mm bending radius attributed to the enhanced connection at the perovskite/carbon interface.

Regulating molecular stacking to construct a superior interfacial contact for highly efficient and stable perovskite solar cells

The non-radiative charge carrier recombination loss at the surface and interface of the perovskite layers in perovskite solar cells (PSCs) is the main cause of their limited power conversion efficiency (PCE). Here we propose an efficient strategy to minimize the non-radiative recombination by introducing symmetric molecules with regular arrangement at the interface between the perovskite layer and hole transport layer (HTL). One end of the symmetric molecule gets in a close contact with the terminal groups of the molecules in the HTL, while the other end promotes connection with the perovskite, resulting in an enhanced interfacial electrical contact and a better valence band energy-level alignment for efficient hole extraction. In contrast, introducing similar but asymmetrical molecules forms a dimer structure and mismatched energy levels at the interface region, which is detrimental to the carrier transport. The best-performing planar PSC with the symmetric molecular modification exhibited an increase in the PCE from 21.05% to 24.02% with a substantially enhanced fill factor of 84.0%, which can be ascribed to the synergistic effects of surface defect passivation and reduction in the interfacial energy barrier. Furthermore, the corresponding unencapsulated PSC retained 80% of the original PCE after 4,000 h of aging in dry air.

Multilateral Passivation Strategy in Post-Synthetic Flexible Metal-Organic Frameworks for Enhancing Perovskite Solar Cells.

The photovoltaic performance of perovskite solar cells is severely limited by the innate defects of perovskite films. Metal-organic framework (MOF)-based additives with luxuriant skeleton structures and tailored functional groups show a huge potential to solve these problems. Here, a multilateral passivation strategy is performed by introducing two alkyl-sulfonic acid functionalized MOFs, MIL-88B-1,3-SO3H and MIL-88B-1,4-SO3H, respectively, obtained from MIL-88B-NH2 through a post-synthetic process, for coordinating the lead defects and inhibiting non-radiative recombination. The flexible MIL-88B-type frameworks endow both functionalized MOFs with excellent electrical conductivity and preferable carrier transport in the hole-transport materials. Compared with the original MIL-88B-NH2 and MIL-88B-1,4-SO3H, MIL-88B-1,3-SO3H exhibits optimal steric hindrance and multiple passivation groups (-NH2, -NH-, and -SO3H), achieving the champion doped device with an enhanced power conversion efficiency (PCE) of 22.44% and excellent stability, which maintains 92.8% of the original PCE under ambient conditions (40% humidity and 25 °C) for 1200 h.

Surface defect passivation of All-Inorganic CsPbI2Br perovskites via fluorinated ionic liquid for efficient Outdoor/Indoor photovoltaics processed in ambient air

All-inorganic α-CsPbI2Br perovskite has garnered considerable interest due to its optical bandgap (∼1.92 eV) suitable for tandem architectures and superior thermal stability. However, CsPbI2Br based perovskite solar cells (PSCs) exhibit severe energy loss due to presence of various surface defects like uncoordinated Pb2+ ions, halide ion vacancies and pinholes, which causes serious non-radiative recombination and limit the further improvement in power conversion efficiency (PCE). Surface passivation strategy is an effective approach to produce high quality α-CsPbI2Br film. Herein, we introduce fluorinated ionic liquid, 3-(Trifluoromethyl) benzylamine (CFBA), as surface passivating agent. The chemical analysis shows that the trifluoro (-CF3) and amine groups of CFBA strongly interacted with perovskite surface via forming Pb-F and H-I bonding, respectively. The high electronegative fluoride atoms of -CF3 group allow for electrostatic interaction with uncoordinated Pb2+ ions, which built a robust shield that protected against surrounding moisture as well. In addition, CFBA modification passivates the dangling bonds, enhanced crystallinity, reduced pinholes, improved the surface coverage and compactness, increased hydrophobicity, and decreased non-radiative recombination, leading to high PCE. With optimum concentration of 3 μL-CFBA, CsPbI2Br PSC revealed an impressive PCE of 17.07% with FF of 83.21% as compared to pristine device (PCE of 15.24% with FF of 79.81%). Moreover, champion device showed an excellent thermal stability by retaining ∼ 86.23% of its initial PCE, whereas pristine device maintained ∼ 48.26% of its original PCE after 1440 h aging at 85 ℃ in a dry box without any encapsulation. In addition, optimized PSC showed a decent indoor PCE of 23.24% as compared to pristine device (18.35%) under dim lighting conditions (LED, 3200 K) at 1000 lx. These results suggested that surface passivation strategy with CFBA is a promising approach for developing efficient all-inorganic CsPbI2Br outdoor/indoor PSCs with better thermal stability.

Multifunctional Metal-organic Frameworks Capsules Modulate Reactivity of Lead Iodide toward Efficient Perovskite Solar Cells with Ultraviolet Resistance.

The two-step sequential deposition process is demonstrated as a reliable technology for the fabrication of efficient perovskite solar cells (PVSCs). However, the complete conversion of dense PbI2 to perovskite in planar PVSCs is tough without mesoporous titanium dioxide as support. Herein, multifunctional capsules consisting of zeolitic imidazolate framework-8 (ZIF-8) encapsulant and formamidinium iodide (FAI) are introduced between tin oxide (SnO2 ) and lead iodide (PbI2 ) layer. Intriguingly, the capsule dopant interlayer benefits the formation of porous PbI2 film due to the porous nanostructure of ZIF-8 which is favorable for the subsequent intercalation reaction. Furthermore, the constituent of the perovskite precursor in ZIF-8 pores can convert into the crystal nuclei of perovskite by reacting with PbI2 first, thereby promoting further perovskite crystallization. Significantly, the incorporation of ZIF-8 can enhance the resistance of perovskite against ultraviolet (UV) illumination due to down-conversion effect. Consequently, the modified device achieves a champion power conversion efficiency (PCE) of 24.08% and displays enhanced UV stability, which can sustain 83% of its original PCE under 365nm UV illumination for 300h. Moreover, the unencapsulated device maintains 90% of initial PCE after 1500h storage in dark ambient conditions with a relative humidity range of 50∼70%. This article is protected by copyright. All rights reserved.

Simultaneously Achieved Defect Passivation and Crystallization Modulation by a Multifunctional Pseudohalogen Salt for Efficient and Stable Perovskite Solar Cells

The accumulation of defects and ion migration at the surfaces and grain boundaries of perovskite impedes the improvement of performance and stability in perovskite solar cells. Therefore, developing strategies to reduce trap‐assisted nonradiative recombination and suppress ion migration in perovskite films is urgently needed. Herein, a multifunctional pseudohalogen salt additive, (benzotriazol‐1‐yloxy) dipyrrolidinocarbenium hexafluorophosphate (denoted as BDPF6), composed of a benzotriazole derivative cation and hexafluorophosphate anion, is incorporated into the perovskite precursor solution. The anion vacancies of perovskite films are filled by , whereas the cation and anion in BDPF6 form ionic and coordination bonds with the perovskites. The BDPF6 additive promotes the crystallization of perovskite films with large grain size, reducing defect densities, prolonging carrier lifetimes, and inhibiting ion migration. Thus, the power conversion efficiency (PCE) of the BDPF6‐modified device remarkably improves from 20.36% to 22.68%. The unencapsulated BDPF6‐modified device maintains 97% of its initial PCE after 1,400 h of exposure to an ambient environment with a relative humidity of 10–20%, whereas the control device maintains only 85% of its initial PCE. Similarly, the BDPF6‐modified device maintains 78% of its original PCE after aging at 60 °C for 1,400 h, whereas the control device only maintains 55%.

Bilayer Indium Tin Oxide Electrodes for Deformation‐Free Ultrathin Flexible Perovskite Solar Cells

The superior electrical conductivity and optical transparency of indium tin oxide (ITO) make it an ideal electrode material for use in optoelectronic devices such as solar cells. When ITO electrodes are fabricated on very thin plastic substrates, however, the internal stress of the ITO layer causes the substrate to deform, severely limiting the device's performance. Herein, it is shown that ITO bilayers composed of an amorphous base layer and a crystalline overlayer lead to deformation‐free ITO electrodes. It is shown that an optimized bilayer structure is achieved when the internal stresses of the amorphous and crystalline layers approximately cancel. With this approach, mixed composition metal halide perovskite solar cells with ITO electrodes are successfully fabricated on 4 μm polyethylene naphthalate films. A power conversion efficiency (PCE) of 18.2% is obtained for the reference cell design, corresponding to a power‐to‐weight ratio of 24 W g−1 before encapsulation. The devices retain 95% of the original PCE after 1000 bend cycles, while under simulated indoor lighting (white LED, 200 lux, 5000 K) the PCE reaches 28.3%. A 3‐cell module with a designated area of 2.3 cm2 is realized with a power output of 28.1 mW and an open‐circuit voltage of 3.17 V.

Interfacial modification to improve all-inorganic perovskite solar cells by a multifunctional 4-aminodiphenylamine layer

All-inorganic carbon-based perovskite solar cells (PSCs) offer low costs and a favorable balance between stability and power conversion efficiency (PCE). Although bulk perovskites are defect tolerant, the defect-mediated carrier nonradiative recombination at the interface between perovskite and carbon layers limits the device performance and stability. In this study, a new 4-aminodiphenylamine (4-ADPA) interlayer was applied to modify the surface and grain boundaries of CsPbI2Br perovskite films. The 4-ADPA layer passivated defects by binding with undercoordinated lead and halide ions at the surface, resulting in the improved thin film quality, reduced defects, and suppressed carrier recombination. All-inorganic CsPbI2Br PSCs by 4-ADPA passivation achieved a PCE of 11.16% with reduced hysteresis and open-circuit voltage loss. In addition, the 4-ADPA passivation inhibited the degradation of the perovskite films in ambient conditions. After storing in air at 25 °C and 25% relative humidity for 700 h, the unpackaged PSC retains 80% of the original PCE. The all-inorganic PSCs with greatly improved device performance and stability would have great prospects in practical applications.

Perylene diimide derivatives with diverse ionic functionality as cathode interlayer for ZnO-free inverted non-fullerene organic solar cells

Perylene diimide (PDIN) derivatives with diverse ionic functionality are prepared and applied to inverted-type non-fullerene organic solar cells (NFOSCs) as the cathode interlayer (CIL). Among PDIN derivatives, PDIN-O is generally applied as the CIL in conventional NFOSCs. As for conventional-type NFOSCs, heat treatment after the deposition of CIL is not necessary because its thermal stability is not considerable. However, the application of PDIN-O as the CIL in inverted-type devices becomes challenging due to the intrinsic property of PDIN-O being unstable under heat treatment and tending to degrade. In this study, we prepare quaternary ammonium salts (PDIN-I and PDIN-Br) and zwitterion (PDIN-BS) as the CIL to enhance thermal stability. We discover PDIN derivatives with diverse ionic functionality can substitute the ZnO layer with the comparable power conversion efficiency. In addition, these CIL retained their original power conversion efficiency after 30 hours of thermal and photo-aging, proving their effectiveness as an oxygen-blocking layer at the device interface. By introducing a diverse ionic functionality to adjust the energy level alignment at the cathode interface, the side group enhances the electron extraction in the devices. This study demonstrates the capacity to regulate CIL and thus provides insight into the fabrication of low-temperature processible ZnO-free NFOSCs.

Perovskite solar cells using NaF additive with enhanced stability under air environment

In this study, we report a facile method to enhance the photovoltaic performance of solar cells based on carbon-counter-electrode by introducing NaF additives into the CH3NH3PbI3 (MAPbI3) film. The NaF additives can not only promote the crystallization of perovskite polycrystals but also help to form uniform, high-coverage, and high-quality perovskite films, leading to better light absorption and hydrophobicity. The device with addition of NaF has a maximum power conversion efficiency (PCE) of 11.26%, which is significantly higher than those without NaF (7.66%). Furthermore, the devices with the NaF additive exhibit superior stability, as they retained more than 95% of the original PCE after 2400 h in a humid atmosphere, which is considered to be associated with the presence of NaF and carbon electrode.

Zwitterionic Ionic Liquid as Additive for High‐Performance FAPbI3 Perovskite Solar Cells with Negligible Hysteresis

Imidazolium‐based ionic liquids have been established as promising candidates for additives in perovskite solar cells. Herein, 1‐(1‐ethyl‐3‐imidazolium)propane‐3‐sulfonate (EIMS) zwitterionic ionic liquid is studied as additive to enhance the performance of the FAPbI3 perovskite solar cells. The addition of EIMS leads to the generation of porous PbI2 film, which promotes the reaction of PbI2 with FAI solution and thus improves the quality of FAPbI3 perovskite film during the two‐step sequential spin coating. It is revealed that EIMS accelerates the extraction of electron, inhibits the formation of pinhole, and reduces the defect density, which leads to an increased efficiency of 22.1%. The hysteresis index is also reduced from 0.142 to 0.009, which indicates the addition of EIMS can realize a negligible hysteresis behavior in the solar cells. Moreover, devices prepared with EIMS retain above 96% of the original power conversion efficiency (PCE) value after being stored in dry air for 45 days. All these results demonstrate that the imidazolium‐based zwitterionic ionic liquid additive strategy is a promising way for high‐performance perovskite solar cells.

Effect of donor groups on the photovoltaic performance of benzothiadiazole-core substituted small molecules for fullerene-based bulk heterojunction organic solar cells

Herein, two symmetric donor-π-acceptor-π-donor-type π-conjugated small molecule donors (BTM and BTP), based on a benzothiadiazole central acceptor core unit and end-capped with electron-donating triphenylamine and 3,5-dimethoxyphenyl)vinyl, are synthesized via a multistep coupling reaction. The structural, thermal, optical, and electrochemical properties of the small molecules are systematically analyzed; subsequently, the molecules are applied as electron donor materials for bulk heterojunction organic solar cell fabrication. Compared with BTM, BTP exhibits a strong absorption spectrum with a precisely tuned optical bandgap (approximately 1.87 eV), desired morphology, and improved interfacial properties. The solar devices fabricated with BTP:PC71BM (1:2.5, w/w) exhibit a higher power conversion efficiency (PCE) of approximately 7.08% with an enhanced current density (JSC) of approximately 12.90 mA/cm2, high open-circuit voltage (VOC) of approximately 0.989 V, and fill factor (FF) of approximately 55.5% compared with BTM-based devices (approximately 4.86%). Notably, the high VOC achieved for the BTP:PC71BM (1:2.5, w/w) devices is a result of the deep-lying HOMO energy level and low LUMO energy offset (approximately 0.51 eV) between the BTP donor and PC71BM acceptor. The high hydrophobicity and stable surface morphology of BTP:PC71BM (1:2.5, w/w) exhibits a high room temperature stability approximately > 94% and retain 6.70% of PCE of its original PCE (7.08%) after 288 hr.

Fe2O3–NiO doped carbon counter electrode for high-performance and long-term stable photovoltaic perovskite solar cells

Perovskite solar cells (PSCs) based on carbon have been viable contenders in the field of photovoltaic due to their low cost, outstanding stability in high-humidity atmospheric air, and high electrical conductivity. Also, using inexpensive counter electrodes with PSCs devoid of organic hole transport materials (OHTMs) might be one way to get around the cost problem. Herein, at first, two different metal oxide nanoparticles (Fe2O3-NPs and NiO-NPs) were synthesized by a novel and cost-effective process. Then these nanoparticles were doped in carbon paste as a hole-transporting material (HTM) to improve charge extraction, interface contact, and energy level alignment, as well as reduction of energy loss, charge recombination, and perovskite surface degradation. The photovoltaic properties of these devices were investigated. All cells showed better efficiency than the control cell, but Fe2O3–NiO@C had better performance with high hole conductivity, matched energy level, and staircase band alignment of perovskite/Fe2O3–NiO@C. Fe2O3 has a higher valence band (VB) than NiO, which facilitates the holes transfer from perovskite and NiO to counter electrode and accelerates the separation of photogenerated electron–holes. The optimal device, FTO/c-TiO2/m-TiO2/perovskite/Fe2O3–NiO@C, achieves a power conversion efficiency (PCE) of 13.27% without encapsulation, compared to the control device (9.49%), and has outstanding long-term stability, retaining almost 82% of its initial efficiency over 720 h. The control device, FTO/c-TiO2/m-TiO2/perovskite/C, kept 66% of the original PCE after 720 h. Therefore, the PSCs based on Fe2O3–NiO doped carbon demonstrated substantial PCE and have good stability in ambient settings, thus making them one of the least expensive PSCs to commercialize.