Improvement Of Photovoltaic Performance Research Articles

Cascade Förster Resonance Energy Transfer Studies for Enhancement of Light Harvesting on Dye-Sensitized Solar Cells.

This work reports cascade Förster resonance energy transfer (FRET)-based n-type (ZnO) and p-type (NiO) dye-sensitized solar cells (DSSCs), discussing approaches to enhance their overall performance. Although DSSCs suffer from poorer performance than other solar cells, the use of composites with carbon dot (Cdot) can enhance the power conversion efficiency (PCE) of DSSCs. However, further improvements are demanded through molecular design to stimulate DSSCs. Here, a photosensitized system based on a cascade FRET was induced alongside the conventional photosensitizer dye (N719). To N719 in a DSSC is transferred the energy cascaded through donor fluorescence materials (pyrene, 3-acetyl-7-N,N-diethyl-coumarin or coumarin and acridine orange), and this process enhances the light-harvesting properties of the sensitizers in the DSSC across a broad region of the solar spectrum. PCE values of 10.7 and 11.3% were achieved for ZnO/Cdot and NiO/Cdot DSSCs, respectively. These high PCE values result from the energy transfer among multi-photosensitizers (cascade FRET fluorophores, N719, and Cdot). Moreover, Cdot can play a role in intensifying the adsorption of dyes and discouraging charge recombination on the semiconductor. The present results raise expectations that a significant improvement in photovoltaic performance can be attained of DSSCs exploiting the cascade FRET photonics phenomenon.

Enhancement of CsPbI3 perovskite solar cells with dual functional passivator 4-Fluoro-3-phenoxybenzaldehyde

All-inorganic perovskite CsPbI3 is an attractive light-absorbing layer material owing to its excellent light-absorbing ability and suitable band gap. However, as the research of perovskite progresses, the negative effects of the defect are further revealed. The uncoordinated Pb2+ and I− vacancies within the perovskite film could inevitably lead to irreversible decay in the power conversion efficiency (PCE) as well as environmental instability for perovskite solar cells (PSCs), impeding the their commercialization process and further improvement in photovoltaic performance. Therefore, the new additive 4-Fluoro-3-phenoxybenzaldehyde (PB) containing fluorine and carboxyl groups is introduced as a dual functional passivator within the perovskite film. Under the cooperative passivation by carboxyl groups and fluorine, the optimized CsPbI3 film exhibits denser morphology, lower density of defect states, as well as enhanced carrier transport properties. Ultimately, a high-performance PSC efficiency of 18.01% with enhanced stability is achieved. The optimized CsPbI3 PSC still maintains 80% of original PCE after 1000 h of illumination with no encapsulation. The key to improving device performance is to fabricate the perovskite film with good morphology, large grain size, and low defect by utilizing the dual passivator of PB.

Graphitic Carbon Nitride Nanostructures as Molecular Modifier for PEDOT:PSS Hole Transport Layer in Polymer Solar Cells

In this article, we introduced graphitic carbon nitride (g-C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> ), a two-dimensional graphene-like material, tuning electronic properties of PEDOT:PSS via secondary doping. The incorporation of g-C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> nanosheets (NS) and quantum dots (QDs) to the aqueous solution of PEDOT:PSS weakens the coulombic interaction between PEDOT and PSS chains, leading to the formation of expanded coil/linear conformational structure. Thereby, increasing the conductivity of doped PEDOT:PSS films by 75% and 30%, respectively, for the optimal doping concentrations of NS and QDs. The polymer solar cell employing these films as hole transport layer (HTL) yielded the power conversion efficiency of 7.65% and 6.44% for NS and QDs, respectively, compared to 5.45% for the reference devices with pristine PEDOT:PSS as HTL. This improvement in photovoltaic performance can be attributed to the increase in short circuit current, carrier mobility, fill factor, and reduced series resistance. The reduced contact barrier, owing to smooth NS and QDs modified HTL, facilitates the charge transport by reducing the overall device resistance by 88% and 30% for NS and QDs, respectively. The modification in the molecular structure of PEDOT:PSS because of the incorporation of NS and QDs resulted in improved device stability retaining almost 40% of the initial PCE even after 200 min of continuous illumination. The results demonstrate a systematic strategy of improving the conductivity and mobility of HTL, resulting in enhanced device performance.

Elucidating the Factors Limiting the Photovoltaic Performance of Mixed Sb–Bi Halide Elpasolite Absorbers

Although Cs2AgBiBr6 halide elpasolites have gained substantial attention as potential nontoxic and stable alternatives to lead–halide perovskites, they are limited by their wide bandgaps &gt;2.2 eV. Alloying with Sb into the pnictogen site has been shown to be an effective method to lower the bandgap, but this has not translated into improvements in photovoltaic (PV) performance. Herein, the underlying causes are investigated. Pinhole‐free films of Cs2Ag(SbxBi1−x)Br6 are achieved through antisolvent dripping, but PV devices still exhibit a reduction in power conversion efficiency from 0.44% ± 0.02% (without Sb) to 0.073% ± 0.007% (90% Sb; lowest bandgap). There is a 0.7 V reduction in the open‐circuit voltage, which correlates with the appearance of a sub‐bandgap state ≈0.7 eV below the optical bandgap in the Sb‐containing elpasolite films, as found in both absorbance and photoluminescence measurements. Through detailed Williamson–Hall analysis, it is found that adding Sb into the elpasolite films leads to an increase in film strain. This strain is relieved through aerosol‐assisted solvent treatment, which reduces both the sub‐bandgap state density and energetic disorder in the films, as well as reducing the fast early decay in the photogenerated carrier population due to trap filling. This work shows that Sb alloying leads to the introduction of extra sub‐bandgap states that limit the PV performance, but can be mitigated through post‐annealing treatment to reduce disorder and strain.

Improvement of charge mobility and photovoltaic performance of small molecule oligothiophene donors through self-assembly

Through molecular engineering of cyanopyridone functionality, herein, two new, small molecule oligothiophene donors, coded as CP7 and CP8, are reported which were designed, synthetically developed, and used in solution-processed bulk-heterojunction devices with the conventional acceptor, PC61BM. Both CP7 and CP8 comprise a common donor, i.e., triphenylamine, a common π-linker, i.e., bis-thiophene, and a cyanopyridone electron accepting group with different substituents at the nitrogen atom of cyanopyridone functionality. The presence of terminal acid group helped to achieve self-assembly of CP7 via hydrogen bonding, and as a result, its pristine and blend film morphologies were superior when compared with the film morphologies based on CP8 (donor oligothiophene comprising terminal ester functionality), thus, affording better device outcome (8.12% (CP7) vs 5.40% (CP8)). The results demonstrated that the molecular engineering of cyanopyridone-based oligothiophene donors to induce self-assembly and to improve film morphology was a key factor for the enhancement of photovoltaic performance. That being said, the power conversion efficiency of >8% is the highest efficiency number reported in the current literature for cyanopyridone-based small molecule oligothiophene donors.

Photovoltaic Performance Improvement with Phase Change Material Cooling Treatment

Solar energy is a clean, abundant, and low-emission renewable energy source. Photovoltaic (PV) technology can convert solar energy into electrical energy; however, it still has a poor output efficiency since high temperatures can lower PV efficiency. Phase Change Materials (PCM) can absorb latent heat, which can be applied to PV as a passive cooling system. In this study, 50 wp PV was treated without and with PCM as a passive cooling system to determine the PV performance. This study compares three PCM types: soy wax, paraffin, and beeswax. Utilizing the PV-PCM panel temperature modeling technique, the inaccuracy in the experimental data was ascertained. According to the simulation, soy wax, paraffin, and beeswax PV panels had average temperatures of 48.6℃, 45.8℃, and 42.6℃, respectively, at an intensity of 1100 W/m2. The experimental results show that PCM beeswax is the best in reducing the working temperature of PV from 60.7℃ to 52.5℃ at an intensity of 1100 W/m2. The results showed that PV with PCM beeswax treatment as a passive cooler could increase the maximum PV output power of 3.04 Watt and the maximum efficiency of PV by 0.94% by lowering the maximum temperature of PV by 8.2℃ compared to PV without a cooling system.

Assessment and performance analysis of roof-mounted crystalline stand-alone photovoltaic (SAPV) system at selected sites in South Africa

BackgroundTechnology is deployed to take the advantage of the ultimate energy from the sun (solar energy) to be used as heat or clean electricity. This energy is classified as “sustainable energy” or “renewable energy” because it requires a short period to naturally replenish the used energy. The application of solar energy involves the conversion of the natural energy resource into a usable form, either as heat or as electricity. The device consists of solar cells made from semiconductor materials, such as silicon, cadmium telluride, gallium arsenide, and so on. Solar potential is both location- and climate-dependent; it is characterised by low energy intensity and intermittency, which limit its application; an improvement in photovoltaic (PV) system performance will facilitate more deployment of the clean electricity system. Therefore, this study provides PV potential and system information required for reliable and optimised solar PV systems at chosen locations. This work uses a 5-stage solar PV system assessment and system performance evaluation utilising Solargis Prospect software. The PV potential and system performance of nine selected site locations in South Africa was conducted using this method. The nine PV site locations are Bloemfontein (Free State), Germiston (Gauteng), Mahikeng (North-West), Mbombela (Mpumalanga), Musgrave (Kwazulu-Natal), Musina (Limpopo), Port Nolloth (Northern Cape), Port Elizabeth (Eastern Cape), and Worcester (Western Cape).ResultThe results of the study were categorised into PV meteorological and system performance parameters as follows. Photovoltaic meteorological parameters—the site in Mahikeng has the highest global horizontal irradiance (GHI), 2156 kWh/m2, and a corresponding specific PV power output (1819.3 kWh/kWp), closely followed by Bloemfontein (2111.5 kWh/m2, 1819.4 kWh/kWp) and Port Nolloth (2003.2 kWh/m2, 1820.5 kWh/kWp). The lowest GHI (1645.1 kWh/m2) and specific PV power output (1436.6 kWh/kWp) were recorded in Musgrave. Photovoltaic system performance parameters—the range of performance ratio (PR) between 75.8 and 77.7% was reported across the nine sites. This ratio met the acceptable benchmark of PR. The highest specific PV power output loss, 118.8 kWh/kWp, was obtained at sites in Bloemfontein, Mahikeng, and Port Nolloth, while the lowest, 93.8 kWh/kWp, was in Musgrave.ConclusionsThe results of the solar PV potential assessment and the evaluation of PV systems performance in the chosen sites across the nine provinces of South Africa show huge PV potential and energy yield. From the results, it was observed that the range of the yearly average of: (1) GHI among the sites is 1645.1–2156 kWh/m2; (2) direct normal irradiation among the sites is 1785.3–2559.3 kWh/m2; (3) diffuse horizontal irradiation among the sites is 512.5–686kWh/m2; (4) global tilted irradiation among the sites is 1849.2–2397.1 kWh/m2; (5) the temperature (TEMP) among the sites is 16–23 °C; (6) specific PV power output (PVOUT specific) among the sites is 1436.6–1820.5 kWh/kWp; (7) total PV power output (PVOUT total) among the sites is 14.366–2397.1 MWh; and (8) the performance ratio among the sites is 75.8–77.7%. Based on the solar resource and performance results of the PV system obtained, the deployment of monocrystalline solar PV technology in all the considered sites across South Africa is technically viable.

A full range of defect passivation strategy targeting efficient and stable planar perovskite solar cells

Defects and inferior charge transport dynamics within devices are key issues that inhibit the improvements of photovoltaic performance and stability. Developing facile and feasible strategies for synchronous passivation of defects regarding charge transport layers (CTLs), perovskite films and their interfaces, and precise tuning of energy level structure, is a definite way to solve above problems. Herein, we develop a synergistic passivation strategy for perovskite films and bilateral interfaces to improve device performance. Firstly, an appropriate amount of phenylethylammonium chloride is adopted to modify SnO2 electron transport layer (ETL). The complexation reaction between N atoms in –NH2 and Sn4+ improve the agglomeration of SnO2 nanoparticles and film quality of SnO2 ETL. The presence of Cl− ions not only effectively fill oxygen vacancies within SnO2 ETL, but also participate in regulating crystal growth dynamics of perovskite films, thus improving electron transport properties at interface. Subsequently, p-type conducting material N,N'-Bis-(1-naphthalenyl)-N,N'-bis-phenyl-(1,1′-biphenyl)-4,4′-diamine (NPB) is introduced into anti-solvent chlorobenzene during the preparation of perovskite films to further regulate the crystal quality and achieve full-range defect passivation. Particularly, the introduction of NPB helps to construct a gradient heterojunction between upper perovskite film and SpiroOMeTAD hole transport layer, thus reducing the accumulation of hole carriers near interface and further suppressing current–voltage hysteresis behavior of devices. Additionally, the hydrophobicity of NPB and full range of defect passivation greatly enhance the humidity and thermal stability of devices. Finally, a high power conversion efficiency of 21.88% is obtained with suppressed hysteresis and enhanced long-term stability. This work highlights the role of full-range defect passivation on CTLs, perovskite absorption layers and interfacial charge transport properties, which provide a novel concept for constructing high-performance and stable perovskite devices.

Photovoltaic performance improvement of organic solar cell with ZnO nanorod arrays as electron transport layer using carbon quantum dots-incorporated photoactive layer

The carbon quantum dots (CQDs) with astonishing optical and electrical features have been utilized to improve the photovoltaic performance of organic solar cells (OSCs). In this work, CQDs dispersed in isopropanol were incorporated into photoactive layer of poly(3-hexylthiophene) (P3HT):(6,6)-phenyl-C61-butyric acid methyl ester (PC61BM) with different volume concentrations (0, 20, 40, 60 and 80 vt%). ZnO nanorod arrays, serving as the electron transport layer, was prepared on ZnO seed layer-coated fluorine-doped tin oxide (FTO) glass substrates. The CQDs-incorporated P3HT:PC61BM photoactive layers were then spin-coated on top of ZnO and silver (Ag), acting as the top electrode, was deposited via thermal evaporation method. It was found that 40 vt% CQDs-incorporated device demonstrated the highest power conversion efficiency and enhancement of 37% compared to that of the device without CQDs. It is proven that the introduction of CQDs improves the optical absorption, exciton dissociation and charge transport of the OSCs.

Plasmonic ZrN@TiO2 core-shell nanostructure enhancing photovoltaic performance of dye-sensitized solar cells

Adding the plasmon optical material into DSSC photoanode has been demonstrated to be an promising method for enhancing the photoelectric conversion ability of photoanode sensitized with presently commercial dye. Zirconium nitride (ZrN) based on relatively cheap Earth-abundant elements is a highly potential alternative to noble plasmon gold. Herein plasmonic ZrN@TiO2 core-shell nanostructures are fabricated and incorporated into the photoanode of DSSC. Related results show that ZrN@TiO2 nanostructure indeed can efficiently improve the photovoltaic performance of corresponding DSSC. The DSSC doped with ZrN@TiO2 yields the champion power conversion efficiency (PCE) of 8.6%. Spectroscopic investigation and theoretical study demonstrate that plasmon effects originated from ZrN can effectively boost the light absorption of dye molecules and accelerate the photogenerated carrier separation, thus elevating the overall harvesting-conversion efficiency of photoanode for light and contributing to the improvement of DSSC photovoltaic performance. This work may offer a kind of new material support to further develop DSSC and provide experimental foundation for the application of ZrN in other solar energy utilization field.

Multidimensional Function Upgradation of All‐Inorganic CsPbIBr2 Perovskite Film by Doping an Ionic Additive for Carbon–Electrode‐Based Solar Cells

All‐inorganic CsPbIBr2 perovskite solar cells (PSCs) recently demonstrated great superiority for application in tandem and semitransparent photovoltaics because of their excellent phase stability. However, compared to state‐of‐the‐art PSCs, the inferior film quality is harmful for the photovoltaic performance improvement. Herein, a novel ionic additive, tetrabutylammonium hexafluorophosphate (TBAPF6), is employed to improve the all‐inorganic CsPbIBr2 perovskite film quality and passivate detrimental defects. By assembly into carbon–electrode‐based solar cells, a champion efficiency as high as 10.57% is achieved, which is much higher than that of a control device with 8.30% efficiency, mainly attributed to the suppressed non‐radiative recombination. More importantly, the presence of alkyl chains and fluorine atoms in TBAPF6 significantly increases the hydrophobicity of perovskite films and therefore improves the long‐term stability under harsh conditions without encapsulation.

Active phase stabilization and photovoltaic performance improvement in mixed-cation formamidinium cesium lead iodide via dimensional engineering with 5-ammonium valeric acid bromide

Formamidinium (FA)-rich double cation lead iodide perovskites, (CsXFA1-XPbI3), hold an exceptional potential to achieve perovskite solar cells (PSCs) with high efficiencies and long-term stability. However, this potential could be limited by the susceptibility of FA-rich CsXFA1-XPbI3 photoactive phases to undergo conversion into inactive phase under harsh humidity conditions (~ 70% RH) and defect-induced interfacial carrier loss in CsxFA1-xPbI3 PSCs. In this work, the treatment of 5-ammonium valeric acid bromide (5-AVABr) on Cs0.1FA0.9PbI3 films was found to produce a synergistic effect: (i) inducing a low-dimensional (LD) perovskite phase on top of the 3D perovskite and (ii) surface doping with Br, enhancing the perovskite phase stability. Our XRD and SEM results indicated that the LDP has a different structure from the typical 2D (5-AVA)2PbX4 perovskite, but has a composition similar to 5-AVACsFAPbX4 (X: I, Br). Moreover, the optimized 5-AVABr modification increases the carrier lifetime, reduces the surface roughness and tunes the band edges at the surface of LD/3D heterostructure. As a result, the best PSC based on the optimized LD/3D layer achieved a power conversion efficiency (PCE) of over 20% compared to 18.68% for the untreated PSC. Most importantly, the ambient stability of AVABr-treated PSCs was considerably improved, with unencapsulated devices retaining 79.89% of initial PCE after 30 days of storage the ambient environment, compared to 22.02% for the untreated device.

Improvement of Photovoltaic Performance of Cu2ZnSn(S,Se)4 Solar Cells by Modification of Back Electrode Interface with Amorphous Boron Nitride

AbstractAn amorphous boron nitride (aBN) layer is inserted between Cu2ZnSn(S,Se)4 (CZTSSe) films and Mo back electrode of CZTSSe solar cell by magnetron sputtering to mitigate the carrier recombination at back interface by tuning energy band alignment and suppressing formation of secondary phases and Mo(S,Se)2. The effect of the aBN layer on power conversion efficiency (PCE) of CZTSSe solar cell is investigated by numerical simulation and experiment. It is found that PCE is greatly improved via the insertion of suitable thick aBN layer, which is attributed to increased open‐circuit voltage (VOC) and fill factor (FF). By quantitative analysis, it is deduced that the increased VOC originates mainly from decrease in reverse saturation current density (J0), followed by increase in shunt resistance (RSh), and the increased FF is mainly due to the decreased J0, followed by increased RSh and decreased photogenerated current density (JL). By optimizing aBN thickness through tuning sputtering time, the PCE increases from 8.68% of CZTSSe solar cell without the aBN layer to 9.51% of the CZTSSe solar cell with aBN layer. The influence mechanism of the aBN layer on the PCE is suggested by analyzing quantitatively the effect of the aBN layer on JL and electrical parameters.

Sputter-deposited CdMgTe for rear contact to CdSeTe/CdTe solar cells

CdTe-based photovoltaic device performance improvement is predominantly limited by open-circuit voltage. This work approaches the voltage deficit challenge through the incorporation of a cadmium magnesium telluride (CdMgTe) electron reflector layer at the back of 1.5- μm CdSeTe/CdTe absorbers to reduce back-surface recombination through a conduction band offset. A sputtered CdMgTe electron reflector layer permitted low fabrication temperatures and circumvented the intolerance of CdMgTe to thermal processing present in traditional close-space sublimation (CSS)-deposited CdMgTe devices. We demonstrate that sputtered CdMgTe simultaneously promotes the retention of chlorine passivation and magnesium which is not feasible with CSS fabrication. We also show the importance of the Cu and Te back contact order in CdMgTe devices. Through the optimization of the sputtered CdMgTe substrate temperature, doping, and back structure configuration, 1.5 μm CdSeTe/CdTe devices with a sputtered CdMgTe layer achieved an efficiency of 16.0%, significantly higher than with CSS CdMgTe, and demonstrated partial enactment of electron-reflector behavior. • Sputtered CdMgTe electron reflector solar cells achieve higher efficiencies than close-space sublimation-deposited. • Low temperatures of sputtered CdMgTe reduce magnesium diffusion and chlorine loss. • CdTe devices with CdMgTe electron reflectors require back contact optimization. • CdTe voltage improvement with CdMgTe limited by a partial negative back valence band offset.

Broad-Band-Enhanced Plasmonic Perovskite Solar Cells with Irregular Silver Nanomaterials.

The localized surface plasmon resonance (LSPR) from noble metal nanomaterials (NMs) is a promising solution to approach the theoretical efficiency for photovoltaic devices. However, the plasmon resonance of metal NMs with particular shapes and sizes can only be excited within narrow spectral ranges, which can hardly cover the broad-band solar spectrum. To address this issue, in this article, Ag NMs with irregular shapes and sizes are synthesized and embedded in the electron transport layer of perovskite solar cells. With the outstanding conductivity of Ag NMs, the series resistance and charge transfer resistance of the devices are dramatically decreased. The Ag NMs with larger size could enhance the light-trapping of the devices owing to the far-field light scattering effect. The near-field enhancement by LSPR of Ag NMs with a small size mainly contributes to the promotion of carrier transport and extraction. As a result, broad-band improvements in photovoltaic performance are achieved due to the significant enhancement of light absorption and electrical features. The highest power conversion efficiency of the perovskite solar cells increases from 19.52 to 22.42% after the incorporation of Ag NMs.

Polymer Acceptors for High‐Performance All‐Polymer Solar Cells

AbstractAll‐polymer solar cells (all‐PSCs) have attracted considerable attention owing to their pronounced advantages of excellent mechanical flexibility/stretchability and greatly enhanced device stability as compared to other types of organic solar cells (OSCs). Thanks to the extensive research efforts dedicated to the development of polymer acceptors, all‐PSCs have achieved remarkable improvement of photovoltaic performance, recently. This review summarizes the recent progress of polymer acceptors based on the key electron‐deficient building blocks, which include bithiophene imide (BTI) derivatives, boron‐nitrogen coordination bond (B←N)‐incorporated (hetero)arenes, cyano‐functionalized (hetero)arenes, and fused‐ring electron acceptors (FREAs). In addition, single‐component‐based all‐PSCs are also briefly discussed. The structure‐property correlations of polymer acceptors are elaborated in detail. Finally, we offer our insights into the development of new electron‐deficient building blocks with further optimized properties and the polymers built from them for efficient all‐PSCs.

Single-bond-linked oligomeric donors for high performance organic solar cells

The effective design and synthesis of novel small-molecule donors (SMDs) is extremely essential for the in-depth study of the scientific problems of bulk heterojunction morphology and the improvement of photovoltaic performance in organic solar cells (OSCs). Importantly, developing a series of donors with different conjugated central donor (D) units is a remarkable strategy to obtain high-performance donors. Herein, two acceptor-donor-donor-acceptor (A-D-D-A) type oligomeric donors 2DTBDT and 2DTBDT-2T with two dithieno[2,3-d:2′,3′-d']benzo[1,2-b:4,5-b']dithiophene (DTBDT) as D units, without and with bithiophene as the π bridge respectively are designed and synthesized successfully. The central linked-DTBDT unit can provide a larger conjugated plane and promote π electron delocalization, which can effectively improve π-π interactions between donors and regulate the crystallinity. And we found that the π bridge provided 2DTBDT-2T with 12.31% efficiency that is already a high efficiency in OSCs, whereas 2DTBDT with merely 3.63% efficiency, both with 2,2′-((2Z,2′Z)-((12,13-bis(2-ethylhexyl)-3,9-diundecyl-12,13-dihydro-[1,2,5]thiadiazolo[3,4-e]thieno[2,"3′’:4′,5′]thieno[2′,3′:4,5]pyrrolo[3,2-g]thieno[2′,3′:4,5]thieno[3,2-b]indole,10-diyl)bis(methanylylidene))bis(5,6-difluoro-3-oxo-2,3-dihydro-1H-indene-2,1-diylidene)) dimalononitrile (Y6) as the acceptor. We conjecture that the main reason for the different device performance may be ascribed to the different molecular stacking orientation of the oligomeric donors and morphology features of the donors:Y6 blend films. Compared to the predominant face-on orientation of the 2DTBDT neat film, the 2DTBDT-2T neat film performed a preferential edge-on orientation, which obtained a smoother surface, stronger crystallinity and more uniform phase separation in the 2DTBDT-2T:Y6 blend films with nanofiber structure, which delivered higher and more balanced carrier mobilities, the more efficient exciton dissociation and reduced biomolecule recombination, therefore obtaining better power conversion efficiencies (PCEs). We speculate that the transformation of molecular stacking orientation of oligomeric donors is possibly due to that π bridge extended and twisted the molecular structure of 2DTDBT-2T, resulting in an edge-on orientation relative to the substrate. These findings demonstrate that the single-bond-linked donor strategy is an alternative method to design the donors towards high-performance OSCs.

Theoretical study on the multiferroic materials In2FeX (X = V, Cr, Mn, Co, and Ni) O6 for high photovoltaics and photocatalysis performance

The double perovskite multiferroic materials Bi2FeCrO6 have a more remarkable improvement in magnetoelectricity, photovoltaic, and photocatalysis performance than BiFeO3. The novel double perovskite multiferroic materials In2FeX (X = V, Cr, Mn, Co, and Ni) O6 are designed to achieve superior performance (e.g., in ferroelectricity and magnetism photovoltaic and photocatalysis) by density functional theory. The calculation results show that In2FeXO6 (X = V or Cr) O6 could be metastable multiferroic material with high ferroelectric polarization strength, and the ferroelectricity is driven by In-O ions interaction. In2FeVO6 has a suitable bandgap and produces high photoelectric conversion efficiency as excellent ferroelectric photovoltaic materials. In2FeVO6 also absorbs visible light to drive water splitting to produce hydrogen under tensile strain by analyzing the band edge position. These calculation results could guide realizing considerable ferroelectric polarization strength, high photovoltaic performance, and photocatalytic hydrolysis hydrogen production.

Balancing Energy-Level Difference for Efficient n-i-p Perovskite Solar Cells with Cu Electrode

Developing low cost and stable metal electrode is crucial for mass production of perovskite solar cells (PSCs). As an earth-abundant element, Cu becomes an alternative candidate to replace noble metal electrodes such as Au and Ag, due to its comparable physiochemical properties with simultaneously good stability and low cost. However, the undesirable band alignment associated with the device architecture impedes the exploration of efficient Cu-based n-i-p PSCs. Here, we demonstrated the ability of tuning the Fermi level ( E F ) of hole transport layer (HTL) to reduce the energy level difference (Schottky barrier) between HTLs and Cu. Further, we identified that the balance of energy level difference between HTL and adjacent layers (including perovskite and Cu) is crucial to efficient carrier transportation and photovoltaic performance improvement in the PSCs. Under the optimized condition, we achieve a device power conversion efficiency (PCE) of 20.10%, which is the highest on the planar n-i-p PSCs with Cu electrode. Meanwhile, the Cu-based PSCs can maintain 92% of their initial efficiency after 1000 h storage, which is comparable with Au-based devices. The present work not only extends the understanding on the band alignment of neighboring semiconductor functional layer in the device architecture to improve the resulting performance but also suggests great potential of Cu electrode for application in PSCs community.

Universal co-existence of photovoltaics and ferroelectricity from a two-dimensional 3R bilayer BX (X = P, As, Sb)

Intertwined ferroelectricity and photovoltaics in two-dimensional (2D) materials will enable the favorable improvement and control of photovoltaic performances.