Small Solar Cells Research Articles

The importance of enhancing D-Dand A-Astacking simultaneously for the balance of hole and electron mobility of small molecule single-component organic solar cells.

Single-component organic solar cells (SCOSCs) have attracted extensive attention due to their simplified device manufacturing and excellent stability. However, the relationship between morphology and charge carrier mobility in the active layers of SCOSCs is not well understood. In this work, we present a comprehensive investigation on this issue by studying four dyads (fullerenes as acceptor units) used as materials of active layers in small-molecule single-component organic solar cells (SM-SCOSCs), in which dyad 4 created the record of power conversion efficiency (PCE) of SM-SCOSC until now. Utilizing a multiscale theoretical approach, the results identify that the acceptor-acceptor stacking is dominant in amorphous films, significantly improving electron mobility and lowering hole mobility. We also find the importance of achieving a balance between electron and hole mobility to further improve PCE of SM-SCOSC because dyad 4 exhibits a more balanced electron/hole mobility than the other three molecules. These findings indicate the importance of tuning and enhancing donor-donor and acceptor-acceptor stacking simultaneously, offering insights for the design and optimization of future SM-SCOSC.

Small molecular donor materials based on β-β-bridged BODIPY dimers with a triphenylamine or carbazole unit for efficient organic solar cells.

Herein, we have designed and synthesized two novel BODIPY dimer-based small molecules, denoted as ZMH-1 and ZMH-2, covalently linked and functionalized with triphenylamine (TPA) (ZMH-1) and carbazole (CZ) (ZMH-2) units as the electron donor at the 3- and 5-positions of the BODIPY core, respectively. Their optical and electrochemical properties were investigated. We have fabricated all small molecule bulk heterojunction organic solar cells using these BODIPY-based small molecules as electron donors along with fullerene derivative (PC71BM) and medium bandgap non-fullerene acceptor IDT-TC as electron acceptors. The optimized OSCs based on ZMH-1:PC71BM, ZMH-2:PC71BM, ZMH-1:IDT-IC, and ZMH-2:IDT-IC attain overall PCEs of 8.91%, 6.61%, 11.28%, and 5.48%, respectively. Moreover, when a small amount of PC71BM as guest acceptor is added to the binary host ZMH-1:IDT-TC and ZMH-2:IDT-TC, the ternary OSCs based on ZMH-1 and ZMH-2 reach PCEs of 13.70% and 12.71%, respectively.

Smart Dc to DC converter for a Small Drone Based upon Deep Learning Technique

Flying a small robot like a drone needs more conservative energy, small solar cell size needs to robust efficient DC-to-DC converter. Mathematical analysis for finding the optimal duty cycle in the PWM (pulse width modulation) is presented at different supplies voltage, considering a low voltage of 8 volts for low-speed motor rotation speed and 18 volts for high speed of the rotation motor. The dc-dc converter gets the power desired from the small robotic by using a dc-dc buck-boost converter with (PID control, smart tuning different rules fuzzy logic control, and a hybrid fuzzy-PID controller as one solution to be improved the controller to be capable on process any disturbances on the inductor or the desired value of the output voltage of the dc-dc converter

Refining interface compatibility and carrier management via π-π conjugated stacking for efficient and stable perovskite solar cells based on low-temperature processing

ABSTRACT Deficiencies and instability in the ETL, perovskite layer, or their interface contribute to carrier nonradiative recombination losses. To address these issues, we propose an electron collection and injection optimisation strategy that focuses on enhancing the compatibility and charge transfer performance at the ETL-perovskite interface. Our approach involves low-temperature modification TiO2 with pyrimidine-2-carboximidamide acetate (PCA) through π-π stacking, reducing the surface energy and improving the interfacial compatibility. At the same time, a stable organic–inorganic hybrid layer is formed with lead iodide (PbI2) below the perovskite layer. Additionally, we demonstrate long-term ambient stability, with the PSCs retaining approximately 90% of their initial PCE after 100 days. We also fabricate large-area modules, achieving an efficiency of 19.53% with an active area of 36.41 cm2. Highlights The introduction of the π-π stacking multifunctional molecule PCA through a low-temperature process to modify TiO2 film enhances the stability and performance of perovskite solar cells. This novel approach improves interfacial compatibility and reduces defects at the interface, enabling vertically aligned crystal growth of perovskite and increasing the interfacial contact area. By effectively removing two types of Hydroxyl groups over the low-temperature TiO2 film through multiple surface chemical reactions, the strategy mitigates nonradiative recombination, leading to reduced energy losses and improved performance in both small and large-area perovskite solar cell modules.

An experimental study on hybrid control of a solar tracking system to maximize energy harvesting in Jordan

Due to its capacity to maximize the power produced by photovoltaic (PV) panels, solar tracking systems have grown in popularity. However, erratic weather conditions, like cloudy or overcast days, change the panel's preferred orientation. On sunny days, the panel is turned to face the sun's radiation; however, on cloudy or overcast days, diffused radiation alters the optimal position. This has increased the necessity for new search algorithms that control the orientation of the panel to generate the most power feasible regardless of the weather conditions. This study aims at developing a sun-tracking system that can adjust the solar panel's orientation to generate the maximum possible electrical output from solar energy in Jordan, regardless of the local climate. To achieve this; a hybrid controller has been created that combines an open-loop sun monitoring system with a dynamic feedback controller built on an active search algorithm. The suggested algorithm is built on the real-time measurement of the PV panels' waning solar irradiance by using small solar cell 0.6 W. The system switches to the recently proposed circular path finding method to locate the Maximum Power Point Tracking (MPPT) if the instantaneous irradiance level falls below a predetermined threshold (DNI irradiance). As a result of the testing phase, the generated power of a solar panel increased by about 35%, confirming the effectiveness of the newly proposed sun tracker hybrid control system. During experimental test, positive irradiance current noises are appeared, using average filter taking the mean of 100 values for one measurement.

Trifluoromethyl-Substituted Conjugated Random Terpolymers Enable High-Performance Small and Large-Area Organic Solar Cells Using Halogen-Free Solvent.

The advancement of non-fullerene acceptors with crescent-shaped geometry has led to the need for polymer donor improvements. Additionally, there is potential to enhance the photovoltaic parameters in high-efficiency organic solar cells (OSCs). The random copolymerization method is a straightforward and effective strategy to further optimize photoactive morphology and enhance device performance. However, finding a suitable third component in terpolymers remains a crucial challenge. In this study, a series of terpolymer donors (PTF3, PTF5, PTF10, PTF20, and PTF50) is synthesized by introducing varying amounts of the trifluoromethyl-substituted unit (CF3) into the PM6 polymer backbone. Even subtle changes in the CF3 content can significantly enhance all the photovoltaic parameters due to the optimized energy levels, molecular aggregation/miscibility, and bulk-heterojunction morphology of the photoactive materials. Thus, the best binary OSC based on the PTF5:Y6-BO achieves an outstanding power conversion efficiency (PCE) of 18.2% in the unit cell and a PCE of 11.6% in the sub-module device (aperture size: 54.45 cm2 ), when using halogen-free solvent o-xylene. This work showcases the remarkable potential of the easily accessible CF3 unit as a key constituent in the construction of terpolymer donors in high-performance OSCs.

Role of Pi-Electron Density at the Interface of Small Molecule-Sensitized Solar Cells

Conventional dye-sensitized solar cells (DSSCs) involving charge-transfer interfaces face charge injection losses and offsets for TiO2-sensitizer band alignment. The direct charge-transfer mechanism in DSSCs with catechol (CT, 1,2-benzenediol)-based compounds minimizes the injection losses and eliminates band alignment issues, although the photovoltaic performance of the corresponding device is very poor due to the ultrafast (picosecond) recombination of photoexcited electrons. Just as in a natural photosystem, structural selectivity toward inhibition of this recombination needs to be defined. The interfacial electron density and back electron transfer kinetics at the molecular sensitizer–TiO2 interface play a significant role in the overall energy conversion efficiency. Herein, we identified, for the first time, that the π-electron cloud at the sensitizer–TiO2 interface facilitates the degree of recombination. Comparative density functional theory analyses confirmed that these electron clouds act as large recombination sites. Luminol (LM) and isoluminol (ILM) were employed as “small molecule” sensitizers without the cloud, having a secondary amine linker, which increased the photoenergy conversion efficiency of the single-step sensitization-based photovoltaic cell (type-II DSSC) by reducing the recombination. The device with LM exhibited a power-conversion efficiency (PCE) of ca. 1.11% (representing 363% improvement when compared to CT), the highest ever reported in this category. This understanding is insightful for the design of novel small molecular sensitizers for future DSSCs.

Designing of asymmetric non-fullerene based acceptor materials by re-modification of π-spacers with PCE > 20 % for organic solar cell

In this study, four new organic molecules with different compounds called the π-linkers, embedded between dithieno[3,2-b:2′,3′-d]pyrrole donor core and dicyanoindanone end-capped acceptor molecules were theoretically designed and analyzed to be proposed as the new asymmetric small molecule acceptors (SMAs) with the highest power conversion efficiency (PCE) in non-fullerene organic solar cells (OSCs). The charge transportability, stability, electronic, and optical properties were calculated based on the molecular structure analysis with the density functional theory (DFT) approach and the results were compared with dithieno[3,2-b:2′,3′-d]pyrrole based asymmetric SMAs named TPIC with dicyanoindanone end-capped groups. As a result of efficient π-π stacking, the energy differences decreased by 17.71 % and the charge transport increased by 49 %. The molecules showed broad absorption spectra ranging from 400 nm to 1200 nm with significant redshifted wavelength towards the near IR region coupled with low excitation energies. The LUMO energy level of the external donor PM7 is aligned with HOMO energy levels of the architecture acceptor molecules via bandgap tuning and the open-circuit voltage (VOC) increased from 1.002 V to 2.44 V for the highest combination PM7:C4. The efficacious charge transport properties, high excitonic generation with low excitation energies, facile separation, and increased VOC via band-gap tunning; all four designed molecules achieved a champion PCE ranging from 20 % to 34 % at short circuit current density 9, 12, and 15 mA cm−2. The molecules exhibited the highest PCE value for any asymmetric non-fullerene small molecule acceptor-based organic solar cells.

Easy and fast prediction of green solvents for small molecule donor-based organic solar cells through machine learning.

Solubility plays a critical role in many aspects of research (drugs to materials). Solubility parameters are very useful for selecting appropriate solvents/non-solvents for various applications. In the present study, Hansen solubility parameters are predicted using machine learning. More than 40 machine models are tried in the search for the best model. Molecular descriptors and fingerprints are used as inputs to get a comparative view. Machine learning models trained using molecular descriptors have shown higher prediction ability than the model trained using molecular fingerprints. Machine learning models trained using molecular descriptors have shown their potential to be easy and fast models compared to the density functional theory (DFT)/thermodynamic approach. Machine learning creates a "black box" connection to the properties. Therefore, minimal computational cost is required. With the help of the best-trained machine learning model, green solvents are selected for small molecule donors that are used in organic solar cells. Our introduced framework can help to select solvents for organic solar cells in an easy and fast way.

A case study on the thermal-stability of polymerized small molecular acceptor-based polymer solar cells

A case study on the thermal stability of polymerized small molecular acceptor (P50-γ) based PSCs was present. And the result demonstrated the thermal-disaggregation process of polymer donor PBDB-T plays a dominant role in the degenerative efficiency.

Mixed perovskite (MAPbI3-xClx) solar cells using light-emitting conjugated polymer DMP end-capped MDMO-PPV as a hole transport material

A series of solar cells (SCs) with methylammonium mixed halide perovskite active layers with a conjugated polymer (CP) poly[2-methoxy-5-(3,7-dimethyl-octyloxy)-1,4-phenylenevinylene] and end-capped with dimethylphenyl (MDMO-PPV) as a hole transport material (HTM) was fabricated under the same experimental settings, and the performance characteristics of the individual cells were compared. For comparison purposes, we fabricated a perovskite solar cell (PSC) with a lithium bis(trifluoromethanesulfonyl)imide (Li-TFSI)-doped sprio-OMeTAD layer (LiTSO), which showed a power conversion efficiency (PCE) of 7.68 %. The layered solar cell with a structure of TiO2, perovskite and MDMO-PPV layers showed a PCE of 5.32 % and a fill factor of 0.478. The heterojunction solar cell (HJSC) made with a perovskite and MDMO-PPV mix showed a PCE of 5.68 %. The Field emission scanning electron microscope (FESEM) showed that in HJSC, the perovskite and CP were mixed well. However, they did not penetrate deeply into the TiO2 mesoporous layer, which would hinder electron transportation and thus cause efficiency loss. The HJSC structure was tested using different thicknesses of mesoporous TiO2 (m-TiO2). At an optimal m-TiO2 thickness, the blend of perovskite and MDMO-PPV infused up to 350 nm, thus improving the PCE to 7.438 % and retaining 91 % performance even after 4 weeks of continuous operation. The perovskite/conjugated polymer blend also formed a small SC above the m-TiO2 layer, showing complete penetration of the perovskite into the m-TiO2 layer. Additionally, the formation of a pure perovskite layer on top of the TiO2/perovskite and MDMO-PPV covers neatly on top of the perovskite layer and serves as a protective layer as well as a hole transport layer. An additional layer of LiTSO on top of the HJSC further improved the PCE to 7.76 %. The use of a CP as the hole transport layer reduces the dependency on separate materials and improves the device’s stability. It could also pave the way for an easy minimalistic method for integrated, flexible power electronics that contain solar cells (perovskite/conjugated polymer), organic light-emitting diodes, and supercapacitors made of graphene.

The conformational control of small D-A-D organic solar cells for large power conversion efficiency: A deep quantum chemistry analysis

Four naphthalene diimide (NDI) based small organic solar cells have been studied with for photoexcited and photovoltaic properties. Density functional theory and Tamm-Dancoff Approximation (TDA) with range-separation gap tunning have been used for ground and excited state calculations. The theoretical calculated results are highly reliable as the difference between the fundamental energy gap (Eg) and ionization gap (Ig) are nearly same. During this research study, the positions of donor units changed with symmetrical and unsymmetrical attachment sites which produced the interesting results of optoelectronic properties at both ground and excited states. The triphenyl amine (TPA) donor units at unsymmetrical units de-stabilized the HOMO and stabilized the LUMO energy levels significantly. The small vertical excitation energies of NDI-TPA molecules increased the transition coefficients from HOMO to LUMO. The emission rate of electron from S1 excited state to S0 is large for DPA-based molecules due to large vertical emission oscillator strength.

Engineering high-emissive silicon-doped carbon nanodots towards efficient large-area luminescent solar concentrators

Luminescent solar concentrators (LSCs) are devices that can collect sunlight from a large area, concentrating it at the borders of the slab, to achieve efficient photovoltaic conversion when small area solar cells are placed at their edges, realizing building-integrated photovoltaics. Efficient luminophores in terms of high luminescence quantum yield are needed to obtain high-performance LSCs. A key point is the ability to engineer the Stokes shift (i.e. the difference between the maximum of the absorption and emission spectra), to minimize reabsorption processes. In this work, we report novel silicon-doped carbon nanodots (Si-CDs) with an ultrahigh quantum yield (QY) up to 92.3% by a simple hydrothermal method. Thin-film structured LSCs (5 × 5 × 0.2 cm3) with different concentrations of Si-CDs are prepared by dispersing the Si-CDs into polyvinyl pyrrolidone (PVP) matrix, and the optimal power conversion efficiency (PCE) of LSCs can be as high as 4.36%, which is nearly 2.5 times higher than that prepared with silicon-undoped CDs. This Si-CDs/PVP film LSC has a high QY of 80.5%. A large-area LSC (15 × 15 cm2) is also successfully fabricated, which possesses a PCE of 2.06% under natural sunlight irradiation (35 mW·cm−2), one of the best reported values for similar size LSCs. The efficient Si-CDs as luminescent substances for high-efficiency large-area LSCs will further give an impetus to the practical exploitation of LSCs.

An extension of electron acceptor sites around Thiazolothiazole unit for evaluation of large power conversion efficiency: A theoretical insight

Small organic solar cells containing thiazolothiazole unit as an electron acceptor for solution processed bulk heterojunction (BHJ) small donor-acceptor-donor (D-A-D) type materials have been designed and studied theoretically with state-of-the-art density functional theory and time-dependent density functional theory (TD-DFT) for reliable estimation of their excited state and charge transfer photophysical characteristics for estimating their power conversion efficiencies. The suggested possible synthetic routes with complete reaction information have been also provided for synthesis. The electron acceptor sites around the thiazolothiazole unit have been enlarged by introducing different strong electron withdrawing groups and checked their effects on the voltages (VOC) and fill factor (FF) which are the two main parameters directly influences on power conversion efficiencies. Out of five theoretically studied molecules, the experimental reported data of TT-TTPA (Thiazolothiazole-thiaophene triphenyl amine) has been compared with four designed molecules and concluded that extension of acceptor sites significantly contributed towards the better charge transport properties of electron and hole.

Design Approaches of Imide Based Organic Solar Cells with Computational Chemistry State-of-the-art Density Functional Theory: A Perspective Review

Imide-based organic solar cells with their theoretical calculations for small molecule based organic solar cells are highly significant for designing and predicting the series of small organic solar cells with non-fullerene acceptors. In this perspective review, we have provided the series of details about the organic and inorganic solar cells and why the organic solar cells are highly significant to avoid the cost issues and large experimental precautions. Secondly, we have also provided the deep guess about the density functional theory and their role in the theoretical prediction of the highly reliable tools for optoelectronic properties. We hope that this perspective report about the organic solar cells with imide central units and details about the density functional theory opens the new ways for thinking and designing the large number of various others optoelectronic materials.

Washable textile embedded solar cells for self-powered wearables

PurposeSolar cells could make textile-based wearable systems energy independent without the need for battery replacement or recharging; however, their laundry resistance, which is prerequisite for the product acceptance of e-textiles, has been rarely examined. This paper aims to report a systematic study of the laundry durability of solar cells embedded in textiles.Design/methodology/approachThis research included small commercial monocrystalline silicon solar cells which were encapsulated with functional synthetic textile materials using an industrially relevant textile lamination process and found them to reliably endure laundry washing (ISO 6330:2012). The energy harvesting capability of eight textile laminated solar cells was measured after 10–50 cycles of laundry at 40 °C and compared with light transmittance spectroscopy and visual inspection.FindingsFive of the eight textile solar cell samples fully maintained their efficiency over the 50 laundry cycles, whereas the other three showed a 20%–27% decrease. The cells did not cause any visual damage to the fabric. The result indicates that the textile encapsulated solar cell module provides sufficient protection for the solar cells against water, washing agents and mechanical stress to endure repetitive domestic laundry.Research limitations/implicationsThis study used rigid monocrystalline silicon solar cells. Flexible amorphous silicon cells were excluded because of low durability in preliminary tests. Other types of solar cells were not tested.Originality/valueA review of literature reveals the tendency of researchers to avoid standardized textile washing resistance testing. This study removes the most critical obstacle of textile integrated solar energy harvesting, the washing resistance.

Insight the difference of free charge generation in two small molecular accepter organic solar cells

Totally understanding the excitons dissociation in nonfullerene organic solar cells (OSCs) is the first priority for the minimum of the device energy loss and so that it can get the highest power conversion efficiency (PCE). The free charges harvesting is complicated though it has already published some evident examples to investigate this issue by small driving force between donors (D) and accepters (A). Here, a robust minus highest occupied molecular orbital (HOMO) level offset D-A couple unveiled this phenomena in greater depth by a time-resolved photo physical processes. The OSCs D-A heterojunction interfacial doping resonant coupling relaxation effect was observed and found some clues with device open-circuit voltage (Voc) energy loss. It undoubtedly demonstrated the device PCE up to 2.37% by a −0.12 eV HOMO offsets value. It was also found that the donor polymer aggregation behavior was greatly affected by the small molecular acceptor. These results will be beneficial to promote the OSCs comprehensive properties in future.

Designing phenyl-di-p-tolyl-amine-based asymmetric small molecular donor materials with favorable photovoltaic parameters

In the quest to enhance photovoltaic devices' efficiency and swift progress in the organic solar cell, community scientists are focusing on small molecules donors. The four specific donor molecules, namely TDMDN1, TDMDN2, TDMDN3, and TDMDN4, are designed from recently reported synthetic TDMDN reference molecules. The designed molecules TDMDN1-TDMDN4 have phenyl-di-p-tolyl-amine attached with different acceptors (terminal side). Quantum chemical and photovoltaic parameters of TDMDN1-TDMDN4 were estimated through DFT at MPW1PW91/6–31 G+ (d,p) . The parameters that affect the photophysical properties, exciton dynamics, chemical reactivity, and charge mobility of TDMDN1-TDMDN4 were described by calculating absorption profile, transition density matrix, frontier molecular orbit, and density of state, respectively. The result of all analyses demonstrates that TDMDN1-TDMDN4 proved more competent in executing the parameters mentioned above than TDMDN. Among all designed donors, TDMDN4 is recognized as an appropriate material for photovoltaic application due to its encouraging parameters involving reduced HOMO-LUMO energy gap (1.79 eV), lowest transition energy (1.50 eV), and highest λmax value with chloroform (826 nm). The binding energy of TDMDN4 (0.29 eV) has a low value compared to the TDMDN (0.35 eV). In addition, a complex of TDMDN4 with PC61BM further verifies suitable combination. All designed donor molecules are highly recommended to attain suitable photophysical properties in solar cells and thus are proposed for the elite performance of small molecular solar cell devices.

Efficient charge generation and low open circuit voltage loss enable a PCE of 10.3% in small molecule donor and polymer acceptor organic solar cells

Two small donors with alkyl chains close to (Se-1) and away from (Se-2) the donor core were synthesized. Ordered molecular packing and an induced face-on packing by PJ1 enable an efficient charge generation and low Voc loss in the Se-2/PJ1 device.

Role of Iodo-Substituted Subphthalocyanine (Subpcs) π-conjugated aromatic N-fused di-Iminoisonidole units on the performance of non-fullerene small organic solar cells

Four acceptor–donor-acceptor (A-D-A) type of iodo-substituted subphthalocyanine (Subpcs) donor molecules have been designed with π-conjugated rigid tetrahedral geometry in which aromatic ring of three units combined around boron atom bearing a macrocycle core with perpendicular axial ligand. Subphthalocyanine are substituted with four different acceptor moieties (Z)-methyl 3-cyanobut-2-enoate (M1), (Z)-5-ethylidene-3-methyl-2-thioxothiazocidin-4-one (M2), 2-(2-methylene-3-oxo-2,3-dihydroinden-1-ylidene) malononitrile (M3), m-ethyl 2(5-methylene-4-oxo-2-thioxothiazolidin-3-yl) acetate (M4). The expansion of pyrrole ring is increased by benzoannulation of axial group which attached to enhance their HOMO energy levels. The optoelectronic properties of designed ADA subphthalocyanine molecules have been computed with B3LYP/LanL2DZ combination of density functional theory. The energy gap (EH-L) of reference molecule is 2.71 eV. The M2 exhibited the narrow band gap (2.15 eV) among other designed donor molecules due to their strong electron-withdrawing group. This computational study and results showed that these designed molecules have large influence on increasing the performance of organic solar cells as small organic materials.