spiro-OMeTAD In Perovskite Solar Cells Research Articles

Enhancing hole-transport efficiency in (CH3NH3)2CuClxBr4-x perovskite solar cells through functionalization of multi-walled carbon nanotubes

This study addresses the conductivity limitation of conventional hole-transporting layers (HTLs) like Spiro-OMeTAD in perovskite solar cells. We integrate functionalized multi-walled carbon nanotubes (MWCNTs) into Spiro-OMeTAD and examine the impact of chemical oxidation/functionalization of MWCNTs on their application in perovskite solar cells. Various ratios of H2SO4/HNO3 mixture were employed to functionalize MWCNTs, with FTIR analysis confirming functional group attachments on the nanotube walls. Raman spectroscopy was utilized to analyze defect formation in the MWCNTs, while FESEM images displayed both the tubular structure and morphological alterations resulting from functionalization. XRD analysis was conducted to examine the structural variances resulting from different functionalization ratios. A lead-free copper-based perovskite (CH3NH3)2CuBr4-xClx (x = 0.5), synthesized via a straightforward solution method, served as the active material for solar cells. The XRD assessment of the active material confirmed perovskite formation, with morphological analysis revealing a layered structure. Diffuse Reflectance Spectroscopy (DRS) measurements yielded a bandgap of approximately 1.86 eV for the perovskite. Dark I–V measurements were executed for Spiro-OMeTAD films incorporated with pure and functionalized MWCNTs, showcasing improved conductivity attributed to charge carrier conduction via defect passivation. Hybrid solar cells were fabricated with structures such as TiO2/(CH3NH3)2CuBr4-xClx (x = 0.5)/Spiro-OMeTAD/Ag, and TiO2/(CH3NH3)2CuBr4-xClx (x = 0.5)/functionalized MWCNTs/Spiro-OMeTAD/Ag. These cells demonstrated enhanced stability, retaining over 65 % of their initial efficiency after 10 days of storage, attributed to improved moisture permeability inferred from contact angle measurements and XRD analysis. Photovoltaic characterization revealed significant improvements in fill factor (∼70 %), short-circuit current density (2.94 mA), open-circuit voltage (0.70 V), and power conversion efficiency (PCE) (1.6 %) for the FTO/TiO2/(CH3NH3)2CuCl0·5Br3.5/Spiro-MWCNT-1/Ag device.

Towards device stability of perovskite solar cells through low-cost alkyl-terminated SFX-based hole transporting materials and carbon electrodes

Developing cost-effective, high-efficiency, and stable hole transporting materials (HTMs) is crucial for replacing traditional spiro-OMeTAD in perovskite solar cells (PSCs) and achieving sustainable solar energy solutions. This work presents two novel air-stable HTMs based on a spiro[fluorene-9,9′-xanthene] (SFX) core functionalized with N-methylcarbazole (XC2-M) and N-hexylcarbazole (XC2-H) rings. These HTMs were synthesized via a straightforward, three-step process with good overall yields (∼40%) and low production costs. To further reduce device cost, carbon back electrodes were employed. The resulting PSCs, with a structure of FTO/SnO2/Cs0.05FA0.73MA0.22Pb(I0.77Br0.23)3/HTM/C achieved power conversion efficiencies (PCEs) of 13.5% (XC2-M) and 10.2% (XC2-H), comparable to the reference spiro-OMeTAD device (12.2%). The choice of alkyl chain on the HTM significantly impacts film morphology and device stability. The XC2-H device exhibited exceptional long-term stability, retaining approximately 90% of its initial PCE after 720 h of storage in 30–40% humidity air without encapsulation. This surpasses the performance of both the spiro-OMeTAD (55% retention) and XC2-M (68% retention) devices. The superior stability of XC2-H is attributed to its highly hydrophobic nature and the formation of a compact, smooth film due to interdigitation of the hexyl chains. The straightforward synthesis of XC2-H from commercially available materials offers a promising approach for large-scale PSC production.

Fluorinated polymer additives in Spiro-OMeTAD to improve the efficiency and stability of perovskite solar cells

This study demonstrates the transformative impact of incorporating poly(vinylidene fluoride-co-trifluoroethylene) P(VDF-TRFE) as an additive in the hole transport layer (HTL) of 2,2′,7,7′-Tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9′-spirobifluorene (Spiro-OMeTAD). The P(VDF-TRFE) additive forms resilient coordination bonds with 4-tert-butylpyridine (TBP) and lithium bis(trifluoromethanesulfonyl)imide additives, which mitigates TBP evaporation and improves Spiro-OMeTAD film quality. In addition, we observed improvements in solar cell current–voltage characteristics consistent with increased Spiro-OMeTAD conductivity and suppressed non-radiative recombination at the HTL/perovskite interface. P(VDF-TRFE)-integrated devices exhibit an increment in power conversion efficiency (PCE) up to 24.1 % (reverse scan) from a reference PCE of 21.4 %. Furthermore, the unencapsulated P(VDF-TRFE)-integrated devices demonstrate improved stability, retaining over 90 % PCE after 45 days in an ambient atmosphere in the dark and 94 % PCE after 1080 h of continuous light-soaking in a nitrogen environment. This work demonstrates how additive engineering, as exemplified by P(VDF-TRFE), can effectively address stability and performance challenges within Spiro-OMeTAD in perovskite solar cells.

Vapor Phase Infiltration Improves Thermal Stability of Organic Layers in Perovskite Solar Cells

Despite the rapid increase in power conversion efficiency (PCE) of perovskite solar cells (PSCs) over the past decade, stability remains a major roadblock to commercialization. This work shows vapor phase infiltration (VPI) as a tool to create hybrid organic–inorganic layers that improve the stability of organic charge transport layers, such as hole-selective spiro-OMeTAD in PSCs and in other organic electronic devices. Using X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), and grazing incident wide-angle X-ray scattering (GIWAXS), we identify that infiltration of TiOx via VPI hinders the crystallization of the spiro-OMeTAD layer by likely preventing the π–π stacking of the molecules. Infiltrated PSCs retained more than 80% of their original efficiency after an operando stability test of 200 h at 75 °C, double the efficiency retained by devices without infiltration, in which the efficiency rapidly decreases in the first 50 h. This work provides a blueprint for using VPI to stabilize organic charge transport layers via prevention of π–π stacking leading to deleterious crystallization that shortens device lifetimes.

Numerical Study of 25.459% Alloyed Inorganic Lead-Free Perovskite CsSnGeI3-Based Solar Cell by Device Simulation

The toxic lead component as well as the expensive and less stable spiro-OMeTAD in perovskite solar cells (PSCs) pose a great deal of hindrance to their commercial viability. Herein, a computational approach towards modeling and simulation of all inorganic cesium tin-germanium triiodide (CsSnGeI3) based perovskite solar cell was proposed and implemented using solar cell capacitance simulator (SCAPS–1D) tool. Aluminium doped zinc oxide (ZnO:Al) and Copper Iodide (CuI) were used as electron and hole transport layers (ETL and HTL) respectively. The initial device without any optimization gave a power conversion efficiency (PCE) of 24.826%, fill factor (FF) of 86.336%, short circuit current density (Jsc) of 26.174 mA/cm2 and open circuit voltage (Voc) of 1.099 V. On varying the aforementioned parameters individually while keeping others constant, the optimal values are 1000 nm for absorber thickness, 1014 cm-3 for absorber layer defect density, 50 nm for ETL thickness, 1017 cm-3 for ETL doping concentration and 260 K for temperature. Simulating with these optimized values results to PCE of 25.459%, Voc of 1.145 V, Jsc of 25.241 mA/cm2, and a FF of 88.060%. These results indicate that the CsSnGeI3 is a viable alternative absorbing layer for usage in the design of a high PCE perovskite solar cell device.

Tert‑butyl peroxybenzoate-doped spiro-OMeTAD for perovskite solar cells with efficiency over 23%

Perovskite solar cells (PSCs) have made great strides as new generation photovoltaic technology. The hole transport materials (HTMs) play an indispensable part in high performing PSCs. Spiro-OMeTAD (Spiro) is the most frequently used HTM. However, pristine Spiro has low conductivity and poor hole mobility. Additives engineering is considered as an effective strategy to solve the dilemma. Here, an organic peroxide additive tert-butyl peroxybenzoate (TBPB) is introduced into Spiro. TBPB not only promotes the rapid oxidation of Spiro to generate more carriers, but also tunes the HOMO of Spiro to achieve proper energy level matching with perovskite layer. Consequently, the TBPB modified device achieves a power conversion efficiency (PCE) of 23.45% with high fill factor (FF) of 81.97%. Meanwhile, the modification of TBPB improves the hysteresis effect, reproducibility and environmental stability of the device. After 80 days of storage in ambient air (RH 26%), the TBPB-doped unencapsulated PSCs still maintained 88.8% of their initial efficiency.

Sustainable, Efficient, and Scalable Preparation of Pure and Performing Spiro-OMeTAD for Perovskite Solar Cells

The technology of organometal halide perovskites is on the verge of the lab to fab transition due to particularly high efficiencies and low cost of the raw materials employed in the active later. The hole transport layer is a key enabling component of such solar cells and at the same time the one requiring more significant synthetic efforts. Alternative materials with improved sustainability are under constant development, yet 2,2′,7,7′-tetrakis(N,N-di(4-methoxyphenyl)amino)-9,9′-spirobifluorene (Spiro-OMeTAD) still represents the standard in the field. We show that the combination of solventless approaches, chemistry on water, and micellar catalysis gives access to such critical material in a fully sustainable, scalable, and efficient way. Performances are validated in devices delivering results equal to those with standard commercial Spiro-OMeTAD but greatly reducing the overall E-factor─a green chemistry metric measuring the waste/purified product ratio of a synthesis, from 5299 to 555, as well as eliminating chlorinated solvents and hazardous chemicals.

Inhibited Aggregation of Lithium Salt in Spiro-OMeTAD for Perovskite Solar Cells

High-efficiency and stable hole transport materials (HTMs) play an essential role in high-performance planar perovskite solar cells (PSCs). 2,2,7,7-tetrakis(N,N-di-p-methoxyphenylamine)-9,9-spirobi-fluorene (Spiro-OMeTAD) is often used as HTMs in perovskite solar cells because of its excellent characteristics, such as energy level matching with perovskite, good film-forming ability, and high solubility. However, the accumulation and hydrolysis of the common additive Li-TFSI in Spiro-OMeTAD can cause voids/pinholes in the hole transport layer (HTL), which reduces the efficiency of the PSCs. In order to improve the functional characteristics of HTMs, in this work, we first used CsI as a dopant to modify the HTL and reduce the voids in the HTL. A small amount of CsI is introduced into Spiro-OMeTAD together with Li-TFSI and 4-tert-butylpyridine (TBP). It is found that CsI and TBP formed a complex, which prevented the rapid evaporation of TBP and eliminated some cracks in Spiro-OMeTAD. Moreover, the uniformly dispersed TBP inhibits the agglomeration of Li-TFSI in Spiro-OMeTAD, so that the effective oxidation reaction between Spiro-OMeTAD and air produces Spiro-OMeTAD+ in the oxidation state, thereby increasing the conductivity and adjusting the HTL energy. Correspondingly, the PCE of the planar PSC of the CsI-modified Spiro-OMeTAD is up to 13.31%. In contrast, the PSC without CsI modification showed a poor PCE of 10.01%. More importantly, the PSC of Spiro-OMeTAD treated with CsI has negligible hysteresis and excellent long-term stability. Our work provides a low-cost, simple, and effective method for improving the performance of hole transport materials and perovskite solar cells.

Simultaneous ambient long-term conductivity promotion, interfacial modification, ion migration inhibition and anti-deliquescence by MWCNT:NiO in spiro-OMeTAD for perovskite solar cells

Simultaneous ambient long-term conductivity promotion, interfacial modification, ion migration inhibition and anti-deliquescence by MWCNT:NiO in spiro-OMeTAD for perovskite solar cells.

Interface compatibility: how to outperform classical spiro-OMeTAD in perovskite solar cells with carbazole derivatives

A smart choice of the charge extraction materials is strongly impacting the efficiency and stability of perovskite solar cells.

Isoindigo derivatives as promising hole transport materials for perovskite solar cells

The role of hole transport material (HTM) layer is critical to obtain high performances for perovskite solar cells (PSCs). The development of novel HTMs with good stability, low cost, and high hole mobility for PSCs is an essential research direction. Herein, new isoindigo-based HTMs were designed and investigated using density functional theory (DFT) computations combined with Einstein relation and Marcus theory. It was found that the energies of HOMO and LUMO levels were increased with an enhancement in the electron-donating character of substituents located on the diphenylamine moieties. The molecules with X = N(Me)2, NHMe, NH2, OMe, OH, and Me substituents exhibited appropriate energy level alignments with respect to MAPbI3, which indicated the hole could be injected from the MAPbI3 to the designed HTMs. Based on the solvation energies, the designed HTMs would be expected to be soluble in the dichloromethane solvent. The results of the absolute hardness and electrostatic surface potential calculations revealed that the stability of such HTMs was decreased with an increase in the electron-donating character of the substituents positioned onto the diphenylamine groups. All of the designed HTMs, except for the X = OH molecule, illustrated considerably greater hole mobility than that of the Spiro-OMeTAD. In view of the matched HOMO level, good hole mobility, plus acceptable solubility and stability, the designed isoindigo based HTMs would have the potential for replacing the Spiro-OMeTAD in PSCs.

Kalium persulfate as a low-cost and effective dopant for spiro-OMeTAD in high performance and stable planar perovskite solar cells

Hole transport materials (HTMs) play an important role for achieving high performance and stable perovskite solar cells (PSCs). Although the state-of-the-art HTM, spiro-OMeTAD, has been successfully applied in PSCs, it exhibits an inferior conductivity and hole mobility, which hampers its future application in commercial PSCs. In this study, a common and strong inorganic oxidant, kalium persulfate (KPS), is introduced as a p-type dopant into spiro-OMeTAD for PSCs with a regular n-i-p architecture. By the introduction of KPS into spiro-OMeTAD films, we systematically investigated the morphology, optoelectrical properties and energy level of KPS-doped hole transport layer (HTL). The results indicate that the incorporation of KPS could not only oxidize spiro-OMeTAD efficiently, but also suppress ion migration by passivating the defect states at the perovskite surface. Accordingly, the KPS-modified PSC with a champion PCE of 20.23% delivered a stabilized output efficiency of 19.59%, while the control device exhibited an inferior PCE of 18.29% with a stabilized power output of 17.51%. More importantly, the devices employed KPS-doped spiro-OMeTAD exhibited less hysteresis and superior long-term stability. Our study provides an insight for HTL engineering by using a low-cost inorganic oxidant for highly efficient and stable PSCs.

Perylene diimide based low band gap copolymers: synthesis, characterization and their applications in perovskite solar cells

In this study, newly designed perylene diimide based polymers P1 and P2 were synthesized and were used as hole transporting materials in place of the more common spiro-OMeTAD in perovskite solar cells. The co-polymers P1-P2 were synthesized by Suzuki and direct arylation polymerizations of 2,9-bis(7-bromo-9,9-dioctyl-9H-fluoren-2-yl)anthra[2,1,9-def:6,5,10-d’e’f’]diisoquinoline-1,3,8,10(2H,9H)-tetrone M1 with 5,11-bis(2-hexyldecyl)-3,9-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-5,11-dihydoindolo[3,2-b]carbazole M2 and 3-octylthiophene M3, respectively. P1 and P2 exhibit broad absorption spectra in thin film and solution with the absorption extending from the ultraviolet to visible and near infrared region of the solar spectrum. The water contact angles of P1-P2 were determined to be 100.8° and 122.9°, respectively, showing good hydrophobicity for the synthesized copolymers. Both polymers show steady state photoluminescence quenching when blended with perovskite. Perovskite solar cell devices fabricated using P1-P2 in place of spiro-OMeTAD show power conversion efficiencies of 13.02% and 10.74%, respectively and manifest the potential of this class of materials as promising alternatives to conventionally used spiro-OMeTAD.

Comparative Study of Linear and Starburst Ethane-Based Hole-Transporting Materials for Perovskite Solar Cells

Recently, linear and starburst hole-transporting materials (HTMs) have been widely developed as potential alternatives to conventional spiro-OMeTAD in perovskite solar cells (PSCs). Herein, two facile ethane-based HTMs with a linear or starburst shape have been designed and prepared. The molecular structure variations in the photophysical, electrochemical, hole mobility, hydrophobicity, and film-forming, and photovoltaic properties in PSCs are comprehensively investigated. Interestingly, the linear molecule exhibits bathochromic-shift spectra, slightly lower highest occupied molecular orbital (HOMO) energy level, higher hole mobility, and better hydrophobicity than its starburst counterpart. Moreover, photoluminescence study confirmed that the linear molecule rather than the starburst molecule can efficiently extract holes at the perovskite/HTM interface. Consequently, higher efficiency of 16.85% for a doped linear-molecule-based device is obtained compared to that of a starburst counterpart exhibiting a lower efficiency of 14.87%. Moreover, the linear HTM also shows better stability. These results indicate the better application potential of linear HTMs than that of the starburst ones.

Progress on the Synthesis and Application of CuSCN Inorganic Hole Transport Material in Perovskite Solar Cells.

P-type wide bandgap semiconductor materials such as CuI, NiO, Cu2O and CuSCN are currently undergoing intense research as viable alternative hole transport materials (HTMs) to the spiro-OMeTAD in perovskite solar cells (PSCs). Despite 23.3% efficiency of PSCs, there are still a number of issues in addition to the toxicology of Pb such as instability and high-cost of the current HTM that needs to be urgently addressed. To that end, copper thiocyanate (CuSCN) HTMs in addition to robustness have high stability, high hole mobility, and suitable energy levels as compared to spiro-OMeTAD HTM. CuSCN HTM layer use affordable materials, require short synthesis routes, require simple synthetic techniques such as spin-coating and doctor-blading, thus offer a viable way of developing cost-effective PSCs. HTMs play a vital role in PSCs as they can enhance the performance of a device by reducing charge recombination processes. In this review paper, we report on the current progress of CuSCN HTMs that have been reported to date in PSCs. CuSCN HTMs have shown enhanced stability when exposed to weather elements as the solar devices retained their initial efficiency by a greater percentage. The efficiency reported to date is greater than 20% and has a potential of increasing, as well as maintaining thermal stability.

Structure-performance relationship on the asymmetric methoxy substituents of spiro-OMeTAD for perovskite solar cells

The hole-transporting materials (HTMs) play an important role in energy conversion process of perovskite solar cells (PSCs). Here, two spiro-OMeTAD derivatives, 2,4-spiro-OMeTAD and 3,4-spiro-OMeTAD with asymmetric methoxy substituents, have been designed, synthesized and fully characterized. Optimization of the positions of the two methoxy substituents in each of the quadrants was proved to be able to adjust the electronic and optical properties of the HTMs, as investigated by cyclic voltammetry and UV/vis spectroscopy. In particular, PSC devices based on 2,4-spiro-OMeTAD exhibited highly improved photovoltaic performance showing an overall conversion efficiency of 17.2% with excellent stability, which is higher than that of the device derived from spiro-OMeTAD (15.0%) under the same conditions. Besides, 3,4-spiro-OMeTAD based PSCs only achieved a power conversion efficiency of 9.1%, demonstrating a huge influence of HTM structure on the cell performance.

Thiophene and diketopyrrolopyrrole based conjugated polymers as efficient alternatives to spiro-OMeTAD in perovskite solar cells as hole transporting layers

PQT, PBTTT, PDQT and PDBT-co-TT were used to replace spiro-OMeTAD as efficient hole transporting layers in perovskite solar cells.

Computational Verification of So-Called Perovskite Solar Cells as PbI64−-Aligned Solar Cells

Effective sensitizing components in so-called perovskite solar cells (PSC) are lead hexaiodide (PbI64−) salts of PbI64− (MeNH3+)n (n = 2∼4). Density-functional-theory-based molecular modeling (DFT/MM) of X-ray crystalline structure of PbI64−/MeNH3+ salt (FOLLIB) verifies that the packing unit of FOLLIB has UV/Vis absorption spectrum at λmax = 424 nm, giving pale yellow color as complementary color. DFT/MM of the horizontal component in the FOLLIB gives narrow energy gap of 0.3 eV, verifying remarkable semiconducting property through tight alignments of PbI64− components coupled with MeNH3+. DFT/MM of the central PbI64−/MeNH3+ components verifies that the central component has UV/Vis absorption spectra with respective λmax = 570 nm, λmax = 762 nm and λmax = 945 nm, and plays an essential role as panchromatic sensitizers. In addition, their equilibrium geometric structures show slightly hypsochromic UV/Vis absorption spectra at respective λmax = 486 nm, λmax = 560 nm, and λmax = 563 nm as results of migration of MeNH3+ close to PbI64−. DFT/MM also verifies that PbI64− components align tightly to nanocrystalline TiO2 (nc-TiO2) and to spiro-OMeTAD in PSC through electron density induced by van der Waals interaction. Electron density-based alignments of PbI64− components well explain unidirectional and leakage-free electron diffusion leading to high open-circuit voltage in PbI64−-aligned solar cells. At the same time, the semiconducting and panchromatic sensitizing layer of PbI64−/MeNH3+ components contribute to excellent short-circuit photocurrent of PbI64−-aligned solar cells.

Simple synthesis and molecular engineering of low-cost and star-shaped carbazole-based hole transporting materials for highly efficient perovskite solar cells

SGT-405(3,6), developed by tuning the substitution position from (2,7) to (3,6) position of carbazole moiety, is an promising alternative non-spiro type small molecular HTM with low-cost, highTgand excellent performance for existing cost ineffective and synthetically-challenging spiro-OMeTADin perovskite solar cells.

New iridium complex as additive to the spiro-OMeTAD in perovskite solar cells with enhanced stability

A new iridium complex, IrCp*Cl(PyPyz)[TFSI], has been synthesized and used as additive for the hole transporter material, spiro-OMeTAD, in perovskite solar cells. The cells prepared with this Ir additive present higher efficiency than reference cells, and similar to cells prepared with Co additive. We have determined that the presence of metal complexes as additives decreases the recombination rate, as it has been observed by impedance spectroscopy. Very interestingly, while the efficiency after 3 months decreases by 22% and 70% for reference cell and cell with Co additive, respectively, the efficiency of devices containing the Ir additive is only decreased by a 4%.