Perovskite Solar Cells Devices Research Articles

Rational and green functionalization of B,N-C60 by DNA bases devised as incredible electron transport compounds for perovskite photovoltaic devices

Environmentally benign materials were devised to be employed as excellent electron transporting layers (ETLs) in perovskite solar cell (PSC) devices. They were based on B,N-C60 fullerene functionalized with a pyrrolidine ring (fulleropyrrolidine) attached to a thiophene ring and a cyanoethyl group (named F-B,N-C60), which was further functionalized by four deoxyribonucleic acid (DNA) bases from their exocyclic N (in NH/NH2 groups) or endocyclic N atoms. To investigate electronic, optical, structural, and electron mobility characteristics of such compounds, density functional theory (DFT) calculations were done. Lowest unoccupied molecular orbital (LUMO) levels of all ETL samples were deeper than conduction band of perovskite CsFAMAPbIBr in PSCs (except for the two samples F-B,N-C60-G1 and F-B,N-C60-G2) that simply injected electrons from CsFAMAPbIBr toward Ag electrode. Highly extraordinary electron mobilities achieved for B,N-C60 functionalized fullerenes were changed from 5.1245 to 106.2272 cm2V−1s−1 that were about 1016-1018 times larger compared to that of B,N-C60 (3.1844×10−16 cm2V−1s−1). Among all ELs, the two samples F-B,N-C60-G1 and F-B,N-C60-G2 displayed very much larger photovoltaic parameters than the rest of B,N-C60 functionalized ETLs. High fill factor (FF), power conversion efficiency (PCE), and open circuit voltage (VOC) values were measured for the PSCs with the devised ETLs in ranges of 0.795–0.893, 8.4522–22.887%, and 0.468–1.129 V, respectively, establishing they could be applied as remarkable ETL materials for photovoltaics.

Optical Dispersion Data Analysis of Single‐Crystal CH3NH3PbBr3 for Optimized Perovskite Solar Cell Active Layer Absorptance

Proper derivation of CH3NH3PbX3 (MAPbX3; where X = Cl−, Br−, I−) optical constants is a critical step toward the development of high‐performance perovskite devices. To date, the optical dispersions at all wavelengths have been inconsistently characterized by under‐approximating or omitting anomalous spectral features. Herein, a rigorous optical dispersion data analysis of single‐crystal MAPbBr3 involving variable‐angle spectroscopic ellipsometry data appended with transmission intensity data is presented. This approach yields a more robust derivation of the refractive index and extinction coefficient for both anomalous (absorptance) and normal (no absorptance) optical dispersion regimes. Using the derived optical constants, illustrative modeled perovskite solar cell device designs are presented in relation to nonrealistic designs prepared using representative optical constants reported in the literature. In comparison, the derived optical constants enables the modeling of layer thicknesses to maximize absorption by the active layer (MAPbBr3) and minimize parasitic optical absorptance by the nonactive layers at broad angles of incidence (≈0°–70°). This robust derivation of MAPbBr3 optical constants is expected to impact the optical dispersion data analysis of all perovskite analogs and expedite targeted development of, for example, solar cell, light‐emitting diode, photo‐ and X‐ray/γ‐ray detector, and laser system technologies.

Optimizating TiO2 electron transport layer for MAPbBr3 perovskite solar cells by way of Ga doping

The exceptional electron transport performance and high stability of titanium dioxide (TiO2) make it widely used in the electron transport layer (ETL). However, the presence of numerous surface defects in TiO2 layer can lead to unnecessary non-radiative recombination, which reduces carrier mobility and affects the photoelectric conversion efficiency (PCE) of perovskite solar cells (PSCs). Therefore, tremendous researches have been focused on reducing surface defects and improving carrier mobility in TiO2 layer. In this study, we adopted metal gallium (Ga) with high conductivity at room temperature as an optimization strategy to enhance the performance of TiO2 layer. By incorporating metal Ga into the TiO2 precursor solution, we successfully fabricated a TiO2-Ga layer that exhibits reduced surface defects and optimized energy level structure. This provides an efficient pathway for electron transport in perovskite layer. Experimental results demonstrate that (methyl ammonium lead tribromide) MAPbBr3 perovskite solar cell devices based on TiO2-Ga layer achieve nearly 24% higher PCE compared to those based on pure TiO2 layer. This successful optimization strategy utilizing metal Ga offers novel insights and approaches for enhancing the performance of PSCs.

In situ one step growth of amorphous tin oxide electron transport layer for high-performance perovskite solar cells.

Tin oxide used in electron transport layer (ETL) exhibits key role in transmitting electrons and blocking holes in perovskite solar cells (PSCs) device. However, crystal tin oxide nanoparticles (NPs) become necessary to form SnO2 film by method of spin-coating, resulting in possible surface defect and cracks among SnO2 NPs, corresponding to unsatisfied performance PSCs. Herein, an amorphous tin oxide thin film is creatively in situ grew onto Fluorine-doped Tin Oxide (FTO) substrate as ETL. The designed solar cell device with structure of FTO/SnO2/MAPbI3/Sprio-OMeTAD/Ag owns a champion photoelectric conversion efficiency (PCE) up to 17.64%, 76.20% of filling coefficient (FF), and 1.09 V of open-circuit voltage (Voc), in comparing with 16.43%, 64.35% and 1.05 V for control group (crystal tin oxide as ETL), respectively. Besides, the champion device keeps 83.33% of initial PCE under nitrogen (N2) condition for one month, in comparison with 76.09% for control group. This work provides a viable strategy for facile preparing amorphous tin oxide film based ETL in perovskite solar cells.

Facile eco-friendly process for upcycled sustainable perovskite solar cells

Developing a green technology to eliminate the impact of the toxic element Pb and harmful solvent is a challenge for sustainable perovskite solar cells (PSCs). Herein, we report a facile eco-friendly process for upcycled sustainable PSC by screening the polar Pb solubilizers (N,N-dimethylformamide, DMF, dimethyl sulfoxide, DMSO and butylamine, BA) coupling with multi-function potassium iodide (KI) precipitator. We find that DMF with strong Pb-dissolution capacity and weak coupled C = O − Pb adhesion exhibits superb separation and recovery of Pb from obsolete PSC devices. Subsequent closed-loop management of the DMF completely eliminates its potential harm to the ecological environment. Interestingly, the KI precipitator added to the Pb-containing DMF solution not only induces the formation of high-quality PbI2 and thus high-crystallized defect-less perovskite matrix, but also relieves the residual tensile strain stemming from lattice expansion leading to orderly lattice orientation for perovskite crystallization. As a result, the re-fabricated PSC based on recovered components (PbI2, ITO and Ag) shows a PCE of 22.78 % higher than that (20.76 %) of PSC based on fresh components, also exceeding the reported record efficiency of PSCs based on one or more recovered components. Such a stable, environment-friendly, upcycled process of retired PSCs offers a sustainable pathway for eliminating the adverse factors such as toxic Pb leakage and harmful solvent effluence, and thus boost their competitiveness in future energy market.

Rational designing of phenothiazine dioxide based hole transporting materials for efficient perovskite solar cells

In this study, we design five novel non-fullerene end capped acceptor based efficient hole transporting materials (HTMs) from phenothiazine dioxide-based core. MPW1PW91 functional with a 6-31G basis set was employed for all DFT calculations and simulation analysis. By substituting acceptor groups in PDO2, numbers of parameters like band gaps, the frontier molecular orbitals (FMOs), higher absorption parameters, and electronic properties like ionization potential, electron affinity, binding energy, and light harvesting efficiency (LHE) were well tuned. In addition, significant variations in other geometrical parameters such as dipole moment, and reorganizational energy parameters were also noticed for the derived molecules compared to the reference molecule (R). Device performance was analyzed by performing calculations of open circuit voltage (VOC) and fill factor (FF). Consequently, all the designed derivatives demonstrated an improved VOC of 0.84 V for an optimized designed structure. In comparison, it was limited to a VOC of 0.57 V for the reference (R) PDO2, displaying an increment in efficiency which is essential to use these molecules as highly efficient HTMs for perovskite solar cell devices in the future.

Unraveling the rapid ion migration in perovskite solar cells by circuit-switched transient photoelectric technique.

Ion migration activated by illumination is a critical factor responsible for the performance decline and stability degradation of perovskite solar cells (PSCs). While ion migration has been widely believed to be much slower than charge transport, recent research suggests that, despite the lack of understanding of the mechanism, it may also be involved in a series of rapid photoelectric responses of PSCs. Here, we report an improved circuit-switched transient photoelectric technique with nanosecond temporal resolution, which enables quantitative characterization of ion migration dynamics in PSCs across a fairly broad time window. Specifically, ion migration occurring within microseconds after illumination (corresponding to a diffusion length of ∼10-7cm) is unambiguously identified. In conjunction with the composition engineering protocol, we justify that it arises from the short-range migration of halide anions and organic cations around the contact/perovskite interface. The rapid ion migration kinetics revealed in this work strongly complement the well-established ion migration model, which offers new insights into the mechanism of ion-carrier interaction in PSC devices.

Top-Down Induced Crystallization Orientation toward Highly Efficient p-i-n Perovskite Solar Cells.

Crystallization orientation plays a crucial role in determining the performance and stability of perovskite solar cells (PVSCs), whereas effective strategies for realizing oriented perovskite crystallization is still lacking. Herein, a facile and efficient top-down strategy is reported to manipulate the crystallization orientation via treating perovskite wet film with propylamine chloride (PACl) before annealing. The PA+ ions tend to be adsorbed on the (001) facet of the perovskite surface, resulting in the reduced cleavage energy to induce (001) orientation-dominated growth of perovskite film and then reduce the temperature of phase transition, meanwhile, the penetrating Cl ions further regulate the crystallization process. As-prepared (001)-dominant perovskite films exhibit the ameliorative film homogeneity in terms of vertical and horizontal scale, leading to alleviated lattice mismatch and lowered defect density. The resultant PVSC devices deliver a champion power conversion efficiency (PCE) of 25.07% with enhanced stability, and the unencapsulated PVSC device maintains 95% of its initial PCE after 1000 h of operation at the maximum power point under simulated AM 1.5G illumination.

Decreased Accumulation of SnO2 Particles Results from Sodium Citrate Dispersant Assisted Chemical Bath Deposition for High Quality Perovskite Solar Cells

Electron transport layer (ETL) is a crucial part for perovskite solar cells (PSCs). However, leakage current and oxygen vacancies result from little pores grown from sol‐gel method would inevitably deteriorate the performance of ETL. In contrast, thin films prepared by chemical bath deposition (CBD) could significantly restrain the little cracks. Here, SnO2 ETL are prepared by optimized CBD process, sodium citrate (SC) is explored as an auxiliary reagent to disperse ETL, thus enhances the smoothness and conductivity of the ETL, resulting in a pore‐free flat surface morphology and decreased oxygen vacancy, which is favorable for electron transport and deposition of perovskite (PVK). The PVK film fabricated on the oxygen vacancy free substrate demonstrates high quality and decreased defect density, thus effectively prevents the non‐radiative recombination of carriers. As a result, the short‐circuit current (JSC) and open circuit voltage (Voc) of the PSC devices have been obviously improved, leading to increased photoelectric conversion efficiency from 21.03% to 22.04%. Meanwhile, the long‐term and moisture stability have been promoted simultaneously.

Correlation between defect properties and the performance of eco-friendly CsSnI3-based perovskite solar cells

This study investigates the potential use of eco-friendly, all-inorganic cesium tin iodide (CsSnI3) perovskite (PVK) as an absorber layer. Despite having higher temperature stability of CsSnI3, the challenge is to get a uniform and defect-free film that hinders the performance. To accomplish this goal, we investigated several performance-related variables for perovskite solar cells (PSCs), including material defect density (Nt ), transport materials, layer thickness, temperature impacts, and back contact work functions. Negative valence band or conduction band offset values indicate no barrier preventing photogenerated carriers from flowing into the charge transport layers. The simulation result shows that hole transport layer thickness shows a higher impact than electron transport layer thickness. For the PVK thickness of 500 nm and a carrier density of 1018 cm−3, the device offers an optimum power conversion efficiency of 20.1%. The performance is more significantly affected by the defects in the PVK material compared to the defects present at the interface. Higher recombination (Re−h+) occurs at the TiO2–CsSnI3 interface. Defects located within the deep-level trap positioned at the mid-point of the band gap energy (E g) have a negative impact on the performance. The temperature coefficient (C T) is approximately ‒0.367% K‒1, indicating excellent thermal stability in an open environment. The selection of ‘A’ cation, the addition of additives, or carefully controlled fabrication techniques can mitigate the defect. This research shows the strategy for creating defects-free PSC devices, ultimately enhancing performance and the stability.

Enhanced CO2 Electrolysis Through Mn Substitution Coupled with Ni Exsolution in Lanthanum Calcium Titanate Electrodes.

In this study, perovskite oxides La0.3Ca0.6Ni0.05MnxTi0.95- xO3- γ (x = 0, 0.05, 0.10) are investigated as potential solid oxide electrolysis cell cathode materials. The catalytic activity of these cathodes toward CO2 reduction reaction is significantly enhanced through the exsolution of highly active Ni nanoparticles, driven by applying a current of 1.2 A in 97% CO2 - 3% H2O. The performance of La0.3Ca0.6Ni0.05Ti0.95O3-γ is notably improved by co-doping with Mn. Mn dopants enhance the reducibility of Ni, a crucial factor in promoting the in situ exsolution of metallic nanocatalysts in perovskite (ABO3) structures. This improvement is attributed to Mn dopants enabling more flexible coordination, resulting in higher oxygen vacancy concentration, and facilitating oxygen ion migration. Consequently, a higher density of Ni nanoparticles is formed. These oxygen vacancies also improve the adsorption, desorption, and dissociation of CO2 molecules. The dual doping strategy provides enhanced performance without degradation observed after 133h of high-temperature operation, suggesting a reliable cathode material for CO2 electrolysis.

Asymmetric Triphenylethylene-Based Hole Transporting Materials for Highly Efficient Perovskite Solar Cells.

Molecular hole-transporting materials (HTMs) having triphenylethylene central core were designed, synthesized, and employed in perovskite solar cell (PSC) devices. The synthesized HTM derivatives were obtained in a two- or three-step synthetic procedure, and their characteristics were analyzed by various thermoanalytical, optical, photophysical, and photovoltaic techniques. The most efficient PSC device recorded a 23.43% power conversion efficiency. Furthermore, the longevity of the device employing V1509 HTM surpassed that of PSC with state-of-art spiro-OMeTAD as the reference HTM.

Anchoring Charge Selective Self-Assembled Monolayers for Tin-Lead Perovskite Solar Cells.

Self-assembled monolayers (SAMs) have displayed great potential for improving efficiency and stability in p-i-n perovskite solar cells (PSCs). The anchoring of SAMs at the conductiv metal oxide substrates and their interaction with perovskite materials must be rationally tailored to ensure efficient charge carrier extraction and improved quality of the perovskite films. Herein, SAMs molecules with different anchoring groups and spacers to control the interaction with perovskite in the p-i-n mixed Sn-Pb PSCs are selected. It is found that the monolayer with the carboxylate group exhibits appropriate interaction and has a more favorable orientation and arrangement than that of the phosphate group. This results in reduced nonradiative recombination and enhanced crystallinity. In addition, the short chain length leads to an improved energy level alignment of SAMs with perovskite, improving hole extraction. As a result, the narrow bandgap (≈1.25eV) Sn-Pb PSCs show efficiencies of up to 23.1% with an open-circuit voltage of up to 0.89V. Unencapsulated devices retain 93% of their initial efficiency after storage in N2 atmosphere for over 2500 h. Overall, this work highlights the underexplored potential of SAMs for perovskite photovoltaics and provides essential findings on the influence of their structural modification.

OCVD PEDOT-Cl Thin Film Fabricated by SbCl5 Oxidant as the Hole Transport Layer to Enhance the Perovskite Solar Cell Device Stability

oCVD PEDOT-Cl Thin Film Fabricated by SbCl₅ Oxidant as the Hole Transport Layer to Enhance the Perovskite Solar Cell Device Stability

Praseodymium doped nickel oxide as hole-transport layer for efficient planar Perovskite Solar Cells

Hybrid organic/inorganic perovskite solar cells (PSCs) have acquired significant consideration due to high power conversion efficiency (PCE). In PSCs, electron and hole extraction layers have a significant influence on their overall performance. In inverted p-i-n structure-based PSCs, NiOx has been frequently employed as a hole transport layer (HTL) due to its simple processing, wide bandgap, high optical transmittance, excellent chemical stability, and low processing temperature for large-scale fabrication. However, NiOx suffers from low electrical conductivity. Doping of NiOx is an effective technique employed for enhancing electrical as well as optical properties. Herein, the praseodymium doped NiOx (Pr-NiOx) was synthesized by sol-gel method, and films were fabricated to investigate the effect of Pr dopant on the optoelectronic properties and photovoltaic performance of PSCs. Results indicated that Pr doping significantly improved the hole mobility by about threefold and conductivity of NiOx films from 4.68 × 10-6 S cm-1 to 8.27 × 10-6 S cm-1. Moreover, it also enhanced the compactness and interfaces of NiOx HTL. PSCs based on 4 % Pr-doped NiOx HTL- yielded PCE of 9.35 % which is 32.43 % more than the PSCs fabricated using undoped NiOx HTL. The enhanced PCE of PSC devices with Pr-doped NiOx could be attributed to efficient extraction of a hole from an active absorbing layer of perovskite thereby, lowering the probability of unsuitable charge carrier recombination. This work exhibits that Pr-doped NiOx thin film could be a promising alternative material for efficient and stable inverted PSCs.

Thickness dependent numerical investigations of lead free perovskite/CIGS bilayer solar cell using SCAPS-1D

Due to the toxicity and the complex fabrication process lead-based perovskite solar cells are difficult to fabricate commercially though the power conversion efficiency has reached 25.2 ​%. In the current scenario, lead free perovskite solar cell devices are gaining interest among the researchers and the bilayer structure is showing significant improvement in the efficiency. In this work, with the help of SCAPS 1D, a lead free single-layer perovskite (CH3NH3SnBr3) solar cell and a bilayer structure (CH3NH3SnBr3/CIGS) have been investigated to compare the photovoltaic performance by using PCBM ([6,6]-phenyl-C61-butyric acid methyl ester) and SnTe as an electron transport layer (ETL) and hole transport layer (HTL) respectively. Different device parameters i.e. thickness, defect density, doping concentration and series-shunt resistance of the device was optimized to obtain the best performance. In the case of a single absorber layer, power conversion efficiency (PCE), open circuit voltage (Voc), fill factor (FF) and the short circuit current density (Jsc) were achieved 20.58 ​%, 0.931 ​V, 64.95 ​% and 34.03 mA.cm−2 respectively. However, it is observed that bilayer structure (FTO/PCBM/CH3NH3SnBr3/CIGS/ZnTe/SnTe/Au) obtains 22.68 ​% of PCE, 0.916 ​V of Voc, 71.46 ​% of FF and 34.66 mA.cm−2 of Jsc. This study suggests that a proper bilayer structure is beneficial to improve the device performance in terms of Jsc and FF by increasing the carrier generation and reducing the back surface field recombination.

Hole-Transporting Materials based on Oligo(hetero)aryls with a Naphthodithiophene Core - Succinct Synthesis by Twofold Direct C-H Olefination.

This work demonstrated the first synthetic application of direct C-H olefinations in the step-saving preparation of various hole-transporting materials (HTM) for efficient perovskite solar cells (PSC). Cross-dehydrogenative couplings of naphthodithiophene (NDT) with vinyl arenes under palladium-catalysis facilely generated various new oligo(hetero)aryls with internal alkenes. Reaction conditions were optimized, which gave the product isolated yields of up to 71 % with high (E)-stereoselectivity. These readily accessible NDT core-based small molecules involving olefin as π-spacers displayed immediate power conversion efficiencies of up to 17.2 % without a device oxidation process that is required for the commercially available spiro-OMeTAD and most other existing HTMs while fabricated in corresponding PSC devices.

Interfacial modification using the cross-linkable tannic acid for highly-efficient perovskite solar cells with excellent stability

Although the performance of perovskite solar cells (PSCs) has been dramatically increased in recent years, stability is still the main obstacle preventing the PSCs from being commercial. PSC device instability can be caused by a variety of reasons, including ions diffusion, surface and grain boundary defects, etc. In this work, the cross-linkable tannic acid (TA) is introduced to modify perovskite film through post-treatment method. The numerous organic functional groups (–OH and CO) in TA can interact with the uncoordinated Pb2+ and I− ions in perovskite, thus passivating defects and inhibiting ions diffusion. In addition, the formed TA network can absorb a small amount of the residual moisture inside the device to protect the perovskite layer. Furthermore, TA modification regulates the energy level of perovskite, and reduces interfacial charge recombination. Ultimately, following TA treatment, the device efficiency is increased significantly from 21.31% to 23.11%, with a decreased hysteresis effect. Notably, the treated device shows excellent air, thermal, and operational stability. In light of this, the readily available, inexpensive TA has the potential to operate as a multipurpose interfacial modifier to increase device efficiency while also enhancing device stability.

Benzoic acid inhibits intrinsic ion migration for efficient and stable perovskite solar cells.

An efficient perovskite solar cell (PSC) has the following characteristics: (1) large perovskite grain size; (2) small ion migration; (3) low defect density states. Here, benzoic acid was employed as an additive to a perovskite solution to improve the thin film quality. Surprisingly, 1.0%-BA can implement all of these features. Therefore, the power conversion efficiency (PCE) of the champion PSC is 18.05%, which is superior to that of the control device (15.42%). In addition, BA-doped PSC kept 86% of its primary PCE after 30 days (RH: 35%), but the control device only retained 75% under the same conditions. The improvement of its stability is because of the inhibition of the cation migration of perovskite by the addition of BA and the passivation of perovskite defects. The results can acquire a better understanding of the potential applications of small organic molecules in improving the PCE and stability of PSC devices.

Rational control of the typical surface defects of hybrid perovskite using tetrahexylammonium iodide.

There are numerous defects existing on the surface and grain boundary of perovskite, which adversely affect the performance and stability of perovskite solar cell devices. Systematic first-principles calculations show that the I vacancy (VI), Pb vacancy (VPb), Pb-I antisite (PbI), and I-Pb antisite (IPb) defects can significantly affect the electronic properties of the surface of formamidinium lead triiodide (FAPbI3); in particular the VPb, PbI and IPb surface defects can introduce defect energy levels in the band gap. Tetrahexylammonium iodide (THAI) that is strongly adsorbed on the (1 0 0) surface of FAPbI3 by forming Pb-I coordination bonds and I⋯H hydrogen bonds could eliminate or reduce the defect states near the band edge or in the band gap by transferring electrons between THAI and the surface of FAPbI3. In particular, the defect states introduced by VPb could be completely eliminated after the adsorption of THAI. This study shows an in-depth understanding of the influence of defects on the electronic properties of the surface of FAPbI3, as well as the passivation mechanism of organic salts on the surface defects of perovskite.