Initial Power Conversion Efficiency Research Articles

Crystallization management and defect passivation via additive engineering for efficient and stable carbon-based CsPbI2Br perovskite solar cells

Inorganic CsPbI2Br perovskite solar cells (PSCs) have attracted enormous interest due to their excellent thermal stability and immense potential for application in tandem solar cells. However, the rambunctious crystallization and poor film quality of inorganic CsPbI2Br perovskite are the main factors limiting their performance improvement. Herein, dibenzoylmethane (DBM), containing electron-rich and dual CO functional groups, as an efficient precursor additive, is first introduced to regulate the crystallization of CsPbI2Br perovskite while passivating its associated defects. After DBM modification, nucleation is accelerated and the crystallinity of CsPbI2Br film is improved, thus promoting the phase stability. Additionally, DBM can passivate uncoordinated Pb2+ defects, thereby significantly reducing non-radiative recombination, and can also decrease the energy level difference between CsPbI2Br/Carbon. As a result, when DBM additive is incorporated in the CsPbI2Br, the power conversion efficiency (PCE) of the device with the fluorine doped tin oxide glass (FTO)/SnO2/CsPbI2Br/Carbon structure is significantly improved to 13.46 %, an increase of nearly 13 % compared to the control device (11.72 %). The unpackaged devices exhibit excellent air and thermal stability, still remaining over 90 % of its initial PCE after aging for 500 h under ambient conditions, or continuous heating at 65 °C in glovebox for 500 h, respectively.

Narrow bandgap Sn-Pb perovskite solar cells with high operational stability modulated by imidazoline derivative

Sn-Pb mixed perovskites with narrow bandgap (NBG) are important for high-performance single- and multi-junction perovskite solar cells (PSCs). However, the inherent Sn2+ oxidation and ion migration lead to inferior stability. Herein, 2-hydrazino-2-imidazoline hydrobromide (2H2I) is employed as a coordinating additive to regulate the film crystallization and inhibit Sn2+ oxidation. Meanwhile, 2H2I can form hydrogen bonds with I− ions to suppress ion migration, thereby improving photovoltaic stability. The target FA0.8Cs0.2Sn0.5Pb0.5I3:2H2I PSC exhibits a champion power conversion efficiency (PCE) of 22.44 %, higher than that of the control device (19.16 %). The target devices retain 90 % (T90) and 80 % (T80) of the initial PCE under maximum power point (MPP) tracking for 1360 h at room temperature and for 436 h at 65 °C, respectively, the highest values for NBG Sn-Pb PSCs. This work demonstrates an effective strategy toward photothermally stable Sn-Pb PSCs.

A Fluorination Strategy and Low-Acidity Anchoring Group in Self-Assembled Molecules for Efficient and Stable Inverted Perovskite Solar Cells.

Herein, we synthesized two donor-acceptor (D-A) type small organic molecules with self-assembly properties, namely MPA-BT-BA and MPA-2FBT-BA, both containing a low acidity anchoring group, benzoic acid. After systematically investigation, it is found that, with the fluorination, the MPA-2FBT-BA demonstrates a lower highest occupied molecular orbital (HOMO) energy level, higher hole mobility, higher hydrophobicity and stronger interaction with the perovskite layer than that of MPA-BT-BA. As a result, the device based-on MPA-2FBT-BA displays a better crystallization and morphology of perovskite layer with larger grain size and less non-radiative recombination. Consequently, the device using MPA-2FBT-BA as hole transport material achieved the power conversion efficiency (PCE) of 20.32 % and remarkable stability. After being kept in an N2 glove box for 116 days, the unsealed PSCs' device retained 93 % of its initial PCE. Even exposed to air with a relative humidity range of 30±5 % for 43 days, its PCE remained above 91 % of its initial condition. This study highlights the vital importance of the fluorination strategy combined with a low acidity anchoring group in SAMs, offering a pathway to achieve efficient and stable PSCs.

Design tungsten oxides hole transport layers (HTLs) to modify the back interface in all-inorganic carbon-based CsPbBr3 solar cells

To enhance the inferior photovoltaic performance of all-inorganic carbon-based perovskite solar cells (C-PSCs) caused by inefficient charge extraction and transport processes of the CsPbBr3/carbon back interface, three types of tungsten oxides (WO3, WO2.72, WO2) are synthesized as low cost and stable hole transport layers (HTLs) to modify the back interface by tunning the energy level alignment. Among the three kinds of tungsten oxides, WO3 shows the best hole extraction and transport capability and the C-PSCs using WO3 HTL generates a power conversion efficiency (PCE) of 7.90% with a high open circuit voltage (Voc) of 1.307 V, indicating a great PCE enhancement of 43.9%, as compared with the device without HTL (5.49%). Meanwhile, WO2.72 and WO2 also are also proved to be qualified HTLs and the devices show PCE values of 7.57% and 6.24%, respectively. Importantly, WO3 and WO2.72 based device show excellent stabilities with PCE retention over 90% of the initial PCE values under ambient conditions for 60 days.

A Synergistic Effect among Multiple Functional Groups of 4‐PyAO Additive for Performance Enhancement of Tin‐Based Perovskite Solar Cells

Tin‐based perovskite is a competitive analog with lead halide perovskite, but there are significant gaps in power conversion efficiency (PCE) and stability between tin‐ and lead‐based perovskite solar cells. The characteristics of the easy oxidizability of Sn2+ and the rapid crystal growth for tin‐based perovskite are two major issues remained to be overcome. Herein, an additive (4‐pyridylamidoxime (4‐PyAO)) with multiple functional groups is introduced in the perovskite precursor solution. The oxidation of Sn2+ and the crystallization rate of perovskite are both retarded by 4‐PyAO addition. The prepared perovskite film is of high quality with fewer trap states and carrier recombination, and carrier extraction and transfer between the perovskite film and the adjacent carrier transport layer also become more efficient. As a result, the corresponding devices deliver the highest PCE of 9.02%, accompanied by short‐circuit current density, open‐circuit voltage, and fill factor of 19.90 mA cm−2, 0.63 V, and 72.48%, respectively. More importantly, the best device without encapsulation maintains 92% of its initial PCE after 2500 h aging test in nitrogen atmosphere, which may be attributed to a synergic effect among the different functional groups.

Fullerene derivatives barrier layer for efficient and stable perovskite solar cells through interfacial modification and removal of superoxide radicals

Superoxide radicals(O2•–)-induced decomposition of perovskite, which seriously impairs the photovoltaic performance and stability of perovskite solar cells (PSCs). Both TiO2 and perovskite produce O2•– that accelerates the rate of catalytic degradation at the interface and inherently poor interfacial contact, exacerbating charge recombination and efficiency loss. Adding fullerene phenol derivative (C60HTB) to the perovskite/TiO2 interface absorbs O2•– and improves poor interfacial communication. The PSCs' power conversion efficiency (PCE) is improved from 20.54 % to 21.63 %. The target devices retained 91.20 %, 94.86 %, and 89.36 % of their initial power conversion efficiencies after 48 h of aging under full-spectrum illumination, 240 h of aging under ultraviolet illumination, and dark storage in air for 500 h, respectively. In this work, efficient and stable TiO2-based-PSCs were realized by scavenging O2•–, which opens a new way to enhance the stability of PSCs in light and O2 environments (light/oxygen).

Performance and stability of hybrid organic-inorganic perovskite photovoltaics in outdoor illuminations conditions

In this study, we conducted real-world outdoor performance and stability tests on two different configurations of perovskite solar cells in the climate conditions of Bahir Dar, Ethiopia. Under outdoor illumination with an incident power of 69 mW cm−2, this device demonstrated a power conversion efficiency (PCE) of 15% for an active area of 0.1 cm2. The maximum power generated, measured at a solar irradiance of 72 mW/ cm2, and was 1.23 mW. The second perovskite device has planar p-i-n configuration. This device achieved a PCE of 18% without masking, but the PCE dropped to 11% when the device was covered with circular aperture mask. Maximum power tracking and stability measurements of the device were conducted. Maximum power generation occurred at operating voltages ranging from 0.8 V to 1.2 V for a device with an active area of 0.095 to 0.1cm2. After 30 days of environmental exposure, the device maintained more than 90% of its initial PCE.

A novel chain-like conjugated donor-π-acceptor molecular additive for highly efficient and stable perovskite solar cells

In donor-π-acceptor (D-π-A) molecules, the coordination ability of the acceptor can be enhanced by the directed movement of delocalized electrons (DEs) on the π-bridge. However, the conventional aromatic ring as π-bridge limits the number of DEs due to the structural characteristic, which restrict the coordination ability of the acceptor, and there is still a lack of research on this issue. Herein, we proposed a chain-like conjugated π-bridge design strategy to address this issue. The Astaxanthin with eleven contiguous C − C = C fragments was selected as a chain-like D-π-A additive for perovskite films. Twenty-two DEs in such chain-like bridge can move towards the C = O group by the D-π-A effect within Astaxanthin, which increases the electron cloud density of C = O group so that enhances its coordination capacity with cations. Ultimately, the Astaxanthin-based device achieved a champion power conversion efficiency (PCE) of 24.43 % and maintained more than 95 % and 91 % of initial PCE for aging 1000 h in dry air (RH < 1 %) and atmosphere (RH = 20 ∼ 30 %), respectively. This work provides a novel strategy to break the restriction of aromatic rings to DEs, which provides theoretical and experimental guidance for further designing chain-like D-π-A additives with strong defect passivation ability to boost photovoltaic performance of PSCs.

Synergetic Exterior and Interfacial Approaches by Colloidal Carbon Quantum Dots for More Stable Perovskite Solar Cells Against UV.

The achievement of both efficiency and stability in perovskite solar cells (PSCs) remains a challenging and actively researched topic. In particular, among different environmental factors, ultraviolet (UV) photons play a pivotal role in contributing to device degradation. In this work, by harvesting simultaneously both the optical and the structural properties of bottom-up-synthesized colloidal carbon quantum dots (CQDs), a cost-effective means is provided to circumvent the UV-induced degradation in PSCs without scarification on their power conversion efficiencies (PCEs). By exploring and optimizing the number of CQDs and the different locations/interfaces of the solar cells where CQDs are applied, a synergetic configuration is achieved where the photovoltaic performance drop due to optical loss is completely compensated by the increased perovskite crystallinity due to interfacial modification. As a result, on the optimized configurations where CQDs are applied both on the exterior front side as an optical layer and at the interface between the electron transport layer and the perovskite absorber, unencapsulated PSCs with PCEs >20% are fabricated which can maintain up to ≈94% of their initial PCE after 100h of degradation in ambient air under continuous UV illumination (5mWcm-2).

A Pseudo Planar Heterojunction Structure for Eco‐Friendly Printable Organic Solar Cells Achieving 19.05% Efficiency

AbstractObtaining a well‐accurate vertical distribution active layer morphology through the air‐printing process is an essential task for achieving efficient scalable large‐area organic solar cells (OSCs). In this target, the desired and controllable pseudo planar heterojunction (PPHJ) active layer structure with suitable phase separation is developed by pre‐deposited D18‐Cl layer under the PM6:BTP‐eC9 film via an eco‐friendly manufacturing method. The addition of the D18‐Cl regulates molecular crystallization and leads to an ideal vertical stratification while simultaneously suppressing voltage loss, optimizing energetic disorder, and carrier management. Impressively, the optimal PPHJ devices perform superior power conversion efficiencies (PCEs) of 19.05% (100 nm), 17.33% (300 nm), and 14.14% (4 cm2) compared to the BHJ devices. Importantly, the PPHJ OSCs also exhibit an impressive extrapolated T80 (the time required to reach 80% of initial PCE) of long‐time storage and operational stability, as well as thermal stability.

Improvement of Thermal Stability and Photoelectric Performance of Cs2PbI2Cl2/CsPbI2.5Br0.5 Perovskite Solar Cells by Triple-Layer Inorganic Hole Transport Materials.

Conventional hole transport layer (HTL) Spiro-OMeTAD requires the addition of hygroscopic dopants due to its low conductivity and hole mobility, resulting in a high preparation cost and poor device stability. Cuprous thiocyanate (CuSCN) is a cost-effective alternative with a suitable energy structure and high hole mobility. However, CuSCN-based perovskite solar cells (PSCs) are affected by environmental factors, and the solvents of an HTL can potentially corrode the perovskite layer. In this study, a Co3O4/CuSCN/Co3O4 sandwich structure was proposed as an HTL for inorganic Cs2PbI2Cl2/CsPbI2.5Br0.5 PSCs to address these issues. The Co3O4 layers can serve as buffer and encapsulation layers, protecting the perovskite layer from solvent-induced corrosion and enhancing hole mobility at the interface. Based on this sandwich structure, the photovoltaic performances of the Cs2PbI2Cl2/CsPbI2.5Br0.5 PSCs are significantly improved, with the power conversion efficiency (PCE) increasing from 9.87% (without Co3O4) to 11.06%. Furthermore, the thermal stability of the devices is also significantly enhanced, retaining 80% of its initial PCE after 40 h of continuous aging at 60 °C. These results indicate that the Co3O4/CuSCN/Co3O4 sandwich structure can effectively mitigate the corrosion of the perovskite layer by solvents of an HTL and significantly improves the photovoltaic performance and thermal stability of devices.

Highly Efficient and Stable Organic Photovoltaic Cells for Underwater Applications.

Organic photovoltaic (OPV) technology holds tremendous promise as a sustainable power source for underwater off-grid systems. However, research on underwater OPV cells is relatively scarce. Here, this gap is addressed by focusing on the exploration and development of OPV cells specifically designed for underwater applications. An acceptor, named ITO-4Cl, with excellent water resistance, is rationally designed and synthesized. Benefiting from its low energetic disorder and an absorption spectrum well-suited to the underwater environment, the ITO-4Cl-based OPV cell achieves an unprecedented power conversion efficiency (PCE) of over 25.6% at a water depth of 1m. Additionally, under 660nm laser irradiation, the cell demonstrates a notable PCE of 31.6%, indicating its potential for underwater wireless energy transfer. Due to the mitigation of thermal effects from solar irradiation, the lifetime of the ITO-4Cl-based OPV cell exceeds 7000h. Additionally, a flexible OPV cell is fabricated that maintains its initial PCE even under exposure to high pressures of 5MPa. A 32.5cm2 flexible module achieves an excellent PCE of 17%. This work fosters a deeper understanding of underwater OPV cells and highlights the promising prospects of OPV cells for underwater applications.

Delaying crystallization and anchoring the grain boundaries defects via π-π stacked molecules for efficient and stable wide-bandgap perovskite solar cells

Owing to the easy migration of halogen ions in wide-bandgap perovskite, it will lead to the formation of a large number of uncoordinated Pb2+ to form deep-level defects, which seriously affects the power conversion efficiency (PCE) and stability of wide-bandgap perovskite solar cells (PSCs). The introduction of additives has been recognized as an effective method to improve these defects, especially Lewis acid-base additives. Herein, Lewis base molecule dibenzofuran (DBF) with π-conjugated system, which can form π-π stacked dimer, is used as a perovskite additive. The detailed crystallization process of perovskite main precursor triggered by DBF is measured by using laser scanning confocal microscopy. It is demonstrated that the addition of DBF in perovskite samples resulted in a deceleration of the crystallization process, which is due to the formation of Lewis acid-base complexes between DBF π-π stacked dimer and perovskite, which can obtain perovskite films with reduced defect density. As a result, the champion PCE of the wide-bandgap (1.68 eV) perovskite device reaches 20.18 %, significantly higher than the control device (17.79 %). Additionally, the device with no encapsulation demonstrates better stability, as it maintains over 90 % of the initial PCE under an air environment with 30–40 % relative humidity (RH) and 25 °C for 1200 h.

High‐Quality Additive‐Free α‐FAPbI3 Film Fabricated by Alkane/Nanocrystals Method and Surface Chemistry Modulation for Efficient Perovskite Solar Cell

AbstractIt's still a scientific issue to synthesize exotic amines‐free and pure‐phase FAPbI3 film because most FAPbI3 films are synthesized by adding MACl‐like exotic amines salts in their precursor solution to reduce the phase transition barrier. In this work, high‐quality and additive‐free phase‐pure α‐FAPbI3 films are successfully fabricated via the sustainable Alkane/Nanocrystals method. FAPbI3 nanocrystals (NCs) are performed as the heterogeneous nuclei to promote the nucleation and crystallization of FAPbI3 films. Cryogenic‐TEM and in situ GIWAXS evidence the seed function and interesting phase evolution of FAPbI3 NCs. The whole phase transition course of pure FAPbI3 film is systematically studied. IR‐AFM and ToF‐SIMS reveal ligands capped on NCs are extruded to the film surface. PbAc‐IPA solution treating the film surface can effectively wash off the surplus ligands at the surface and modulate the surface chemistry and energy levels. As a result, an average power conversion efficiency (PCE) of 21.45% is achieved for MA‐free pure α‐FAPbI3 perovskite solar cells (PSCs), as well as the best light‐soaking stability record of retaining 95% of the initial PCE after 800 h. This work paves a new way to fabricate MA‐free pure α‐FAPbI3 PSCs.

Multifunctional Interface Modification Enables Efficient and Stable HTL-Free Carbon-Electroded CsPbI2Br Perovskite Solar Cells.

In recent years, hole transport layer-free all-inorganic CsPbI2Br carbon-electroded perovskite solar cells (C-PSCs) have garnered significant attention due to a trade-off between stability and photovoltaic performance. However, there are inevitably many defects generated at the surfaces or grain boundaries of CsPbI2Br perovskite films, which will serve as carrier non-radiative recombination centers, and CsPbI2Br perovskite films are sensitive to water molecules to degrade, together with energy level mismatch between CsPbI2Br perovskite and carbon electrodes. Herein, 1-benzyl-3-methylimidazolium hexafluorophosphate (1-B-3-MIMPF6), an imidazolium-based ionic liquid simultaneously containing benzene ring and fluorine atoms, was introduced for the modification of the perovskite/carbon interface. The results showed that it could effectively reduce defects, enhance carrier transfer, mitigate carrier non-radiative recombination, facilitate energy alignment, and block moisture intrusion. Therefore, the photovoltaic performance of the modified PSCs with ITO/SnO2/CsPbI2Br/1-B-3-MIMPF6/carbon architecture has been boosted with a champion power conversion efficiency (PCE) of 13.47 %, open circuit voltage of 1.20 V, short circuit current density of 14.69 mA/cm2, and fill factor of 76 %. Moreover, the unencapsulated modified devices exhibited an improved stability and the PCE maintained 78 % of their initial PCE after 24 h storage at room temperature in a 30 %-35 % humidity environment, whereas that of the pristine devices dropped to almost zero.

Multifunctional Spacer in 2D/3D Wide‐Bandgap Perovskite for Monolithic Perovskite/Silicon Tandem Solar Cells

To maximize the power conversion efficiency (PCE) and stability of perovskite/silicon tandem solar cells (TSCs), high‐performance and stable perovskite top cells with wide‐bandgaps are required. A 2D/3D wide‐bandgap perovskite with a bandgap of 1.69 eV using 1H‐1,2,4‐triazole‐1‐carboximidamide (1‐TzFACl) as a spacer is developed. The 2D/3D wide‐bandgap perovskite shows better film quality, enhanced crystallinity, suppressed nonradiative recombination, and significantly improved phase stability. Its initial PCE (21.58%) remains above 87% after 1560 h of continuous illumination due to the insertion of Cl− in the perovskite lattice. A monolithic two‐terminal perovskite/silicon TSC achieves a PCE of 25.66% with high light stability. This work provides an ingenious strategy to restrain the phase segregation in wide‐bandgap perovskites, leading to effective and stable perovskite/silicon TSCs.

Green Material Chlorin e6 Passivation Improves the Efficiency of Perovskite Solar Cells

Functional passivation agents have been shown to effectively optimize the crystallization process and passivate defects on the surface and grain boundaries. People have conducted extensive research on the passivation mechanisms of various passivation agents to obtain more effective passivation agents. Researchers are gradually focusing on natural ingredients in the search for suitable passivation agents due to the wide variety, green color, and ease of production. As a result, the natural chlorophyll component chlorin e6 (CE‐6) is first combined with perovskite solar cells (PSCs) to improve their performance. Following the incorporation of CE‐6 into the perovskite layer, various functional groups of CE‐6 are used to effectively reduce traps on the perovskite surface, suppress charge recombination at the interface, improve carrier transfer rate and carrier extraction efficiency, and ultimately improve efficiency. The optimal device achieves a power conversion efficiency (PCE) of 21.14% and maintains its initial PCE of 84% after being stored in a room‐temperature air environment for 500 h. Furthermore, semitransparent PSC (ST‐PSC) is made with 13.33% PCE and 5.53% average visible light transmittance. The findings show that natural material CE‐6 performs well in the perovskite layer and confirms the promising prospects for optimizing ST‐PSC.

Improved charge extraction in inverted perovskite solar cells with dual-site-binding ligands.

Inverted (pin) perovskite solar cells (PSCs) afford improved operating stability in comparison to their nip counterparts but have lagged in power conversion efficiency (PCE). The energetic losses responsible for this PCE deficit in pin PSCs occur primarily at the interfaces between the perovskite and the charge-transport layers. Additive and surface treatments that use passivating ligands usually bind to a single active binding site: This dense packing of electrically resistive passivants perpendicular to the surface may limit the fill factor in pin PSCs. We identified ligands that bind two neighboring lead(II) ion (Pb2+) defect sites in a planar ligand orientation on the perovskite. We fabricated pin PSCs and report a certified quasi-steady state PCE of 26.15 and 24.74% for 0.05- and 1.04-square centimeter illuminated areas, respectively. The devices retain 95% of their initial PCE after 1200 hours of continuous 1 sun maximum power point operation at 65°C.

Synergistic strategies to unveil the dual influence of additive and annealing treatment on the morphology of isatin-derived low bandgap small molecule donor in solution-processed organic solar cells

A novel organic small molecule, 5-(4-(diphenylamino)phenyl)-1-octylindoline-2,3-dione (TPI) containing an alkyl chain substituted electron accepting isatin (indoline-2,3-dione) and strong electron withdrawing N, N-diphenylaniline units have been synthesized through Suzuki coupling reaction. The molecular structure of TPI is confirmed by NMR, FT-IR, and Mass spectroscopy techniques. The TPI molecule exhibits a low band gap of approximately ∼ 2.03 eV which is also supported by the DFT results. The influence of additive and heat treatment on the electronic, morphological, and photovoltaic performance of organic solar cells was investigated meticulously. The TPI donor exhibits complementary light absorption with fullerene acceptor in combination with DIO and TA which efficiently absorb the photon in the 300–730 nm range. The TPI was later used as an electron donor material for the fabrication of organic solar cells. Remarkably, the morphology-dependent optimized TPI:PC71BM (1:3.0) exposed excellent power conversion efficiency (PCE) of about ∼ 5.56 % with enhanced VOC of ∼ 0.811 V, JSC of 11.81 mA cm−2 and FF of 55.3 % fabricated in addition with DIO and thermal annealing treatment. Most importantly, the unencapsulated devices maintained > 96 % of the initial PCE value after 240 h under ambient temperature. Our findings indicate that isatin-derived small molecules with simple architecture propose great potential for promising BHJ-OSCs material.

Spiro-Bifluorene-Cored Dopant-Free Conjugated Polymeric Hole-Transporting Materials Containing Passivation Parts for Inverted Perovskite Solar Cells.

Two spiro-bifluorene-based dopant-free HTMs (X22 and X23) have been synthesized by facilely condensing spiro-bifluorene diamine with 3,4-ethylenedioxythiophene (EDOT)-5,7-dicarbonyl dichloride and 2,3,5,6-tetrafluoro-terephthaloyl dichloride, respectively. In the X22 molecule, lone pairs of electrons on the sulfur (S) and oxygen (O) functional groups interact with the perovskite materials. The hole mobility (μh) of X22 (3.9 × 10-4 cm2 V-1 S1-) is more than twice that of X23 (1.4 × 10-4 cm2 V-1 S1-). The conductivity (σ0) of X22 is 2.73 × 10-4 S cm-1, which is also higher than that of X23 (2.39 × 10-4 S cm-1). The EDOT moiety benefits the contact angle of CH3NH3PbI3 precursor solutions on HTMs as low as 24°. The X22-based device with an indium-doped tin oxide/hole transport material (HTM)/CH3NH3PbI3/phenyl-C61-butyric acid methyl ester (PC61BM)/bathocuproine/Ag structure achieves a power conversion efficiency (PCE) of 19.18%. The PCE of the device based on X23 containing fluorine is 18.70%, and the contact angle between HTM and the perovskite precursor solution is 32°. The X22- and X23-based devices at ambient temperature (≈25 °C) in N2 retain 86% and 79% of the initial PCE after 150 days. The effect of S, O, and F heteroatoms plays an important role in the side chain modification of HTMs, improving defect passivation in HTM/CH3NH3PbI3 interfaces by multiple functional groups.