Enhanced Power Conversion Efficiency Research Articles

Tailoring optoelectronic properties of CH3NH3PbI3 perovskite photovoltaics using al nanoparticle modified PC61BM layer

In photovoltaics, light harvesting is one of the critical factors for the enhancement of power conversion efficiency (PCE). Photon harvesting can be carried out by various methods in perovskite photovoltaic. The improved light harvesting can also be achieved by trapping the light by incorporating metallic nanoparticles at the interface or in the perovskite active layer itself. Either light is absorbed or scattered by metallic nanoparticles depending on the particle size. When light is absorbed by the nanoparticles (size < 20 nm), it behaves like a sub-wavelength antenna due to localized surface plasmon resonance (LSPR) excitation and hence near field effect of plasmonic particle will be interacting to CH3NH3PbI3 active layer. Larger particles (>20 nm) act as sub-wavelength scattering centers of light and help in trapping incident light. In order to make use of dual effect poly-dispersed spherical aluminium nanoparticles (AlNPs) (size – 20–70 nm) were incorporated in the CH3NH3PbI3 perovskite solar cell at the PC61BM/Al electrode interface. As a result, there is an increase in the optical absorption in the AlNPs embedded device. A detailed study of optical absorption, absorbed light emission characteristics charge trap density and carrier concentration studies, photovoltaic property measurements indicates, improvement in power conversion efficiency arise due to enhancement in JSC. Evaluated device properties indicate that enhancement in JSC arises due to improvement in the active layer photon absorption by both scattering and plasmonic effect in addition to reduced series resistance.

Bicontinuous network of electron donor-acceptor composites achieved by additive-free sequential deposition for efficient polymer solar cells

We report that sequential deposition of a highly crystalline polymer donor and a soluble fullerene acceptor leads to a well-defined interpenetrating network and enhanced power conversion efficiencies in bilayer polymer solar cells. Even without the use of solvent additives, layered thin films of poly[(5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl)-alt-(3,3‴-di(2-octyldodecyl)-2,2’; 5′,2’’; 5″,2‴-quaterthiophen-5,5‴-diyl)] (PffBT4T-2OD) and [6,6]-phenyl C71-butyric acid methyl ester (PC71BM), as electron donor and acceptor materials, respectively, showed bicontinuous networks similar to those of a PffBT4T-2OD:PC71BM bulk-heterojunction (BHJ) thin film processed with 1,8-diiodooctane (DIO) as a solvent additive. Transmission electron microscopy results confirmed the BHJ-like morphology of the bilayered PffBT4T-2OD/PC71BM thin films. Bilayer solar cells fabricated without the DIO additive produced a power conversion efficiency of η ≈ 7.65%, which is even higher than that of a BHJ solar cell fabricated with the DIO additive (η ≈ 7.04%). These results demonstrate that a highly crystalline polymer donor and an electron-accepting small molecule can be a good combination for efficient bilayer polymer solar cells.

Role of Regeneration of Nanoclusters in Dictating the Power Conversion Efficiency of Metal-Nanocluster-Sensitized Solar Cells.

Metal nanoclusters (NCs) have emerged as feasible alternatives to dyes and quantum dots in light energy conversion applications. Despite the remarkable enhancement in power conversion efficiency (PCE) in recent years and the increase in the number of NCs available as sensitizers, a comprehensive understanding of the various interfacial charge-transfer, transport, and recombination events in NCs is still lacking. This understanding is vital to the establishment of design principles for an efficient photoelectrode that uses NCs. In this work, we carefully design a comparison study of two representative NCs, Au and Ag, based on transient absorption spectroscopy and electrochemical impedance spectroscopy, methods that shed light on the true benefits and limitations of NC sensitizers. Low NC regeneration efficiency is the most critical factor that limits the performance of metal-nanocluster-sensitized solar cells (MCSSCs). The slow regeneration that results from sluggish hole transfer kinetics not only limits photocurrent generation efficiency but also has a profound effect on the stability of MCSSCs. This finding calls for urgent attention to the development of an efficient redox couple that has a great hole-extraction ability and no corrosive nature. This work also reveals different interfacial behaviors of Au and Ag NCs in photoelectrodes, suggesting that utilizing the benefits of both types of NCs simultaneously by cosensitization or using AuAg alloy NCs may be one avenue for further PCE improvement in MCSSCs.

Efficient planar heterojunction perovskite solar cells with enhanced FTO/SnO2 interface electronic coupling

Abstract Ultrathin and compact SnOx amorphous layers derived from SnCl4 were introduced at the interface of electron transport layer (ETL)/perovskite or FTO/ETL to enhance the electron coupling between layers, passivate the trapping defects and optimize the energy level alignment. As results of the increased interface electron collection and reduced interface recombination, the planer perovskite solar cell (PSC) with SnO2 nanocrystal (NC) ETL pre-treated by SnCl4 (Cl-SnO2) shows the power conversion efficiency (PCE) enhancement from 16.3% to 18.6%, and the device hysteresis has also been significantly restrained. In comparison, the planer PSCs with traditional SnCl4 (SnO2-Cl) post-treated SnO2 NC ETL makes the PCE increased from 16.3% to 17.3%. These results indicate that both two kinds of treated ways could improve the performance of the PSCs but compared with the post-treatment process, the devices based on Cl-SnO2 pre-treated ETL present superior performance, which is attributed to the closer contact and enhanced electron coupling between FTO and SnO2 NC ETL with Cl-SnO2 in between.

Novel CuAlO2/polyaniline hole transport layer for industrial production of perovskite solar cells

Here, we report the application of a CuAlO2/polyaniline (PANI) film, prepared using a large-area-compatible electrospray process, as a hole transport layer in a perovskite solar cell. The synergistic combination of CuAlO2 and PANI results in enhanced hole extraction, a smoother perovskite/hole transport layer interface, and an 80 % enhancement in power conversion efficiency. The results reveal that CuAlO2/PANI film has potential as a low-cost, scalable hole transport layer for perovskite solar cells.

Asymmetrically Alkyl‐Substituted Wide‐Bandgap Nonfullerene Acceptor for Organic Solar Cells

An asymmetric wide‐bandgap (WBG) nonfullerene acceptor (C6‐IDTT‐T) is developed by shearing one alkyl side‐chain from a symmetrically alkyl‐substituted indacenodithieno[3,2‐b]thiophene (IDTT) core of the fused‐ring electron acceptor 2C6‐IDTT‐T. These two acceptors both exhibit wide optical bandgaps over 1.8 eV. Investigations on the optical, electrochemical, and active layer morphology are conducted to understand the effect of asymmetric side chains on the electrical and photovoltaic properties. Compared with symmetric 2C6‐IDTT‐T, asymmetric C6‐IDTT‐T is found to exhibit redshifted absorption and higher electron mobility. As a result, the C6‐IDTT‐T blend with a thienothiophene‐benzodithiophene copolymer (PTB7‐Th) presents higher electron mobility and more balanced charge carrier transport, which leads to an enhanced power conversion efficiency of 8.51% for C6‐IDTT‐T‐based device with a high open‐circuit voltage of 1.052 V and a low energy loss of 0.60 eV.

Base-catalyzed synthesis of superhydrophobic and antireflective films for enhanced photoelectronic applications

In this work, a facile, cost-effective and environmentally friendly approach is developed to synthesize transparent silica sol for fabricating antireflective (AR) and superhydrophobic (SH) films on soda–lime glass. The transparent silica sol is prepared at room temperature by modification of hexamethyl disilazane (HMDS) on colloidal silica nanoparticles (NPs) which are synthesized via base-catalyzed hydrolysis of tetraethoxysilane (TEOS) in the presence of ammonia-free alkaline solution (i.e., NaOH). The AR and SH silica films are then achieved by dip-coating. The average transmittance, water static contact angle (CA) and sliding angle (SA) of the resulting film can reach 93.1%, 169.7° and 3.0°, respectively, exhibiting both AR and SH properties. In particular, the excellent SH and AR properties of the resulting film facilitate not only the excellent self-cleaning performance but also the increasing light transmittance and thus an enhanced power conversion efficiency (PCE) in photovoltaic module.

Development of Block Copolymers with Poly(3-hexylthiophene) Segments as Compatibilizers in Non-Fullerene Organic Solar Cells.

Poly(3-hexylthiophene) (P3HT)-segment-based block copolymers have been reported to deliver an effective compatibilizer function in the P3HT:PC61BM bulk-heterojunction (BHJ) system to simultaneously improve performance and stability. However, as limited by the deficient optophysic properties of the P3HT:PC61BM system, the resultant power conversion efficiency (PCE) of compatibilizer-mediated devices is low despite the optimized chemical structures of the P3HT-segment-based block copolymers. To better shed light on such a compatibilizer effect, the compatibilizer function of the P3HT-segment-based block copolymers is herein investigated in the emerging non-fullerene acceptor (NFA)-based BHJ systems. A P3HT analogue, poly[(4,4'-bis(2-butyloctoxycarbonyl-[2,2'-bithiophene]-5,5-diyl)-alt-(2,2'-bithiophene-5,5'-diyl))] (PDCBT), is used as the polymer donor since it shares the same backbone as P3HT to afford good compatibility with the P3HT-segment-based block copolymers and it has been proven to deliver a higher PCE than P3HT in the NFA BHJ systems. The P3HT-segment-based block copolymers (P1-P4) are manifested to offer similar compatibilizer functions for the PDCBT-based NFA BHJ systems, and the importance of their structural design is also revealed. As a result, addition of P4 delivers the largest enhancement in PCE: from 5.30 to 7.11% for the PDCBT:ITIC blend and from 6.21 to 8.04% for the PDCBT:IT-M blend. Moreover, it can also enhance the device's thermal stability, which can maintain 77% of the initial PCE after annealing at 85 °C for 120 h (for the PDCBT:ITIC blend), outperforming the pristine binary device (66% preservation). More importantly, the entire compatibilizer-mediated device exhibits an improved Voc. Such reduced potential loss can be attributed to the improved interfacial compatibility between the photoactive components, the most important function of a compatibilizer.

Deep‐Ultraviolet Photoactivation‐Assisted Contact Engineering Toward High‐Efficiency and Stable All‐Inorganic CsPbI2Br Perovskite Solar Cells

All‐inorganic perovskite CsPbI2Br have been regarded as a promising candidate to tackle the thermal instability issue of organic–inorganic perovskite solar cells. However, the serious interfacial charge recombination and large voltage potential loss in cells circumscribe their performance and commercialization. Herein, a facile approach is demonstrated in which the SnO2 electron transport layer is modified with short‐period deep‐ultraviolet (DUV) photoactivation process to decrease the work function and achieve better energy alignment with the conduction band of perovskites. Such modification triggers efficient charge transfer and reduces the charge recombination. Moreover, first‐principles calculation further demonstrates that DUV‐treated SnO2 can strengthen the interface interaction, reduce the interface stress caused by lattice mismatch, induce more ordered perovskite structure, enlarge transfer charge from 0.71 to 2.33 e, gain larger built‐in field (from 0.74 to 2.09 eV), lower work function, and smaller conduction band offset. Thus, all‐inorganic CsPbI2Br solar cells based on DUV‐treated SnO2 exhibit a significant enhancement in power conversion efficiency, and the champion cell achieves an elevated efficiency of 15.1% with a superior Voc of 1.22 V and better stability.

Toward efficient polymer solar cells with thick bulk heterojunction by introducing iridium complex as an aggregation reshaping auxiliary

The morphology control of thick bulk heterojunction (BHJ) polymer solar cells (PSCs) is an important factor to determine their power conversion efficiency (PCE). Particularly, during the building of phase separation, aggregation morphology plays a prominent role in the control of both horizonal and vertical gradient distribution of donor/acceptor (D/A) in thick BHJ. In this work, we introduced a novel iridium complex of (tfmppy)2Ir(tpip) into the active layer of PffBT4T-2OD: PC71BM as an “aggregation reshaping auxiliary” to form a long and narrow aggregation shape in both horizontal and vertical directions. Through characterizing the morphology of active layer in details, it was found that the combination of 5% (tfmppy)2Ir(tpip) assists PffBT4T-2OD aggregation shape with a 1: 2.5 aspect ratio while maintaining high crystallinity. In addition, the results showed that the (tfmppy)2Ir(tpip) facilitates efficient exciton dissociation and charge transport because of increased contacting area of D/A interface. As a result, the short circuit current (JSC) and fill factor (FF) performances were both improved contemporaneously, leading to a 20.3% enhancement in PCE.

Enhanced carrier mobility and power conversion efficiency of organic solar cells by adding 2D Bi2OS2

Although polymer solar cells (PSCs) have many advantages, they have obtained great progress in the two decades, the low charge carrier mobility still restricts performance progress of PSCs. Two-dimensional (2D) Bi-based semiconductor nanomaterial (Bi2OS2) can be a potential material for improving the charge carrier mobility in the active layer of PSCs, because it exhibits a high carrier mobility, suitable band gap, wide absorption range, and good stability. In this work, we synthesize the 2D Bi2OS2 nanomaterial and incorporate it into active layer of PSCs as a third component for the first time. By introduction 1 wt% 2D Bi2OS2 nanomaterial into the PSCs, the power conversion efficiency (PCE) of PSCs can be obviously improved by more than 17% comparison with binary PSCs (from 10.51% to 12.31%). The enhancement of PCE is mainly due to the improving of charge transport, surface morphology, and crystallization of active layer. It is worth noting that the 2D Bi2OS2 play the role of the heterogeneous nucleation in the active layer, resulting in the enhanced crystallization of PBDB-T and ITIC. These results not only provide a way to improve the performance of PSCs, but also show that the 2D Bi2OS2 nanomaterial has great potential application in the PSCs.

Utility of copper oxide nanoparticles (CuO-NPs) as efficient electron donor material in bulk-heterojunction solar cells with enhanced power conversion efficiency

Abstract In the present work, we have endeavored the utilization of wet-chemically synthesized copper oxide nanoparticles (CuO-NPs) as the active layer in hybrid bulk heterojunction (BHJ) solar cells. The BHJs with CuO-NPs display significantly different physics from customary BHJs, and prove a noteworthy improvement in their performance. It is noted that with the addition of CuO-NPs, the morphology of the photoactive layer endures significant changes. Incorporating CuO-NPs is an additional paradigm for BHJs solar cells which enhances the photocurrent density from 9.43 mA/cm2 to 11.32 mA/cm2 and the external quantum efficiency as well. Also the power-conversion efficiency (PCE) improved from 2.85% to 3.82% without harming the open circuit voltage and the fill factor. The enhancement in PCE achieved here makes it worthy to design high-performance organic solar cells holding inorganic nanoparticles.

Efficient flexible Mo foil-based Cu2ZnSn(S, Se)4 solar cells from In-doping technique

Cation substitution has an important impact on the power conversion efficiency (PCE) of Cu2ZnSn(S,Se)4 (CZTSSe) solar cells. Herein, a significant PCE enhancement of flexible indium-doped CZTSSe solar cells has been achieved by partially substituting Sn4+ with In3+. Systematic measurements indicate that In doping in CZTSSe film effectively improves the crystallinity and carrier concentration of the absorber layer. Meanwhile, the treatment reduces interface recombination and band tailing by passivating deep defects and increases the open-circuit voltage (Voc) of the solar cells. By physical analysis, the key parameters for the solar cell diode such as A, J0, Rs and Rsh are significantly improved after In-doping, indicating better PN junction quality. Under the optimal In-doping (x = In/(Sn + In) = 9%), the flexible Cu2ZnSn1-xInx(S,Se)4 solar cell has been successfully obtained with the best efficiency of 7.19% and the Voc enhancement of 62 mV due to reduced Voc deficit and band tailing.

Underlying effects of diiodooctane as additive on the performance of bulk heterojunction organic solar cells based small organic molecule of isatin-core moiety

This paper reports the synthesis of D-A type π-conjugated organic chromophore, 1-hexyl-5-(5′-hexyl-[2,2′-bithiophen]-5-yl)indoline-2,3-dione (RBTh-NR) using isatin-core moiety as strong electron-acceptor and terminal alkyl bithiophene as electron-donor. The synthesized RBTh-NR chromophore was utilized as donor material for the fabrication of the solution processed bulk heterojunction organic solar cells (BHJ-SMOSCs) and the effects of 1,8-diiodooctane (DIO) as an additive was investigated. Due to the presence of isatin-core moiety, RBTh-NR displayed good optical properties with absorption at ∼526 nm. The obtained cyclicvoltametry (CV) results exhibited good HOMO and LUMO energy levels of −5.24 eV and −3.46 eV, respectively for RBTh-NR thin film. The use of DIO as an additive in an active layer considerably improved the morphology, and also tuned the optical and electrical properties. As compared to the pristine device, the performance of RBTh-NR-PC61BM-DIO (1:3, w/w) active layer based optimized BHJ-SMOSC displayed the better performance with enhanced power conversion efficiency (PCE) of ∼4.10 %, short circuit current density (Jsc) of ∼12.21 mA/cm2 and improved fill factor (FF) of ∼45%.

Poly(3-hexylthiophene) (P3HT) and Phenyl-C61-Butyric Acid Methyl Ester (PC61BM) Based Bulk Heterojunction Solar Cells Containing Silica and Titanium Dioxide Nanorods: Molecular Dynamics Simulations.

Molecular dynamics simulations are used to demonstrate the effects of introducing anisotropicallyshaped silica (SiO₂) and titanium dioxide (TiO₂) nanoparticles on the morphology of poly(3-hexylthiophene) (P3HT)-phenyl-C61-butyric acid methyl ester (PC61BM) bulk heterojunction (BHJ) solar cells. The morphological compatibility and structure formation upon introduction of nanorods to the mixture of P3HT and PCBM are systematically studied by calculating several parameters that are known to influence the performance of BHJ. The anisotropically-shaped nanorods self-assemble into a variety of macroscopic structures, depending on the aspect ratio, and alter the phase morphology of PCBM. Several morphological properties such as domain size, crystallinity of the polymer phase and surface area of contact between P3HT and PCBM are found to be influenced by the presence of these nanorods. At low aspect ratios of the nanorods, the nanorod-PCBM clusters formed are kinetically-trapped and heavily branched, resulting in lower P3HT domain size and crystallinity. As the aspect ratio increases, the nanorods align parallel to each other and form two-dimensional sheet-like structures with PCBM. The P3HT crystallinity near the surface of longer nanorods were found to be higher. These changes in the morphological properties of the bulk heterojunction can be used as a benchmark to study the ternary blend solar cells with enhanced power conversion efficiency.

A review on spectral converting nanomaterials as a photoanode layer in dye‐sensitized solar cells with implementation in energy storage devices

AbstractThe present review article aims at the application of rare‐earth‐based titanium dioxide nanocrystals as spectral converters in photovoltaic devices, with special focus on dye‐sensitized solar cells (DSSCs). Additionally, the implementation of DSSCs in energy storage, more importantly, DSSCs and lithium‐ion batteries (LIB) integrated devices are systematically described. The absorption in DSSCs is mainly confined to the visible solar spectrum, which is one of the main reasons behind its limited power conversion efficiency. This has led to shifting of research focus on broadening the light absorption range of DSSCs, which can further lead to enhancement in overall power conversion efficiency. TiO2, doped with rare‐earth (RE) ions, is often used as an electron transport layer (ETL) in DSSCs to overcome this absorption‐related issue. This article gives a detailed review of TiO2 doped with different RE ions, as an electron transport layer in DSSCs. More importantly, we have summarized all the recent important findings with the application of DSSCs in LIB and photocapacitors.

Interfacial engineering and down-conversion of ultraviolet light for efficient perovskite solar cells

The addition of a tiny amount of fluorescent organic material N, N′-di (naphtha-1-yl)-N, N′-diphenyl-benzidine (NPB) into polymeric hole transport layer (HTL) is shown to yield a significant enhancement in down-conversion of ultraviolet (UV) light into visible light. As a result, NPB incorporated HTL based devices exhibit enhancement in power conversion efficiency (PCE) of 18.2% compared to 15.1% for pristine devices. This work demonstrated that fluorescent down-conversion of UV light based on doped HTLs is a novel and effective approach for enhanced performance of perovskite solar cells (PSCs). In addition, the incorporated fluorescent material NPB provides a favorable energetic alignment at the interface for low voltage loss. These results are further supported by time-resolved photoluminescence (TRPL) measurements that are performed on perovskite layers deposited on top of NPB doped Poly (triaryl amine) (PTAA), which shows an improvement in lifetime of the charge carriers with increasing concentration of NPB. An increase in the lifetime of the charge carriers is observed on the perovskite layer that is deposited on top of 2.5 wt% NPB doped PTAA layer. The lifetime enhancement is due to additional charge carriers that are generated from the conversion of high energy photons to low energy photons. These additional charge carriers that are generated in HTL occupy the charge transport states after filling the trap states in the perovskite layer and hence the lifetime of the charge carriers increases. The TRPL lifetime decreases with further increase in the NPB concentration more than 2.5 wt% due to efficient charge carrier extraction.

Dramatic efficiency boost of single-walled carbon nanotube-silicon hybrid solar cells through exposure to ppm nitrogen dioxide in air: An ab-initio assessment of the measured device performances

We observed a 73% enhancement of the power conversion efficiency (PCE) of a photovoltaic cell based on a single wall carbon nanotube/Si hybrid junction after exposing the device to a limited amount (10 ppm) of NO2 diluted in dry air. On the basis of a computational modeling of the junction, this enhancement is discussed in terms of both carbon nanotube (CNT) p-doping, induced by the interaction with the oxidizing molecules, and work function changes across the junction. Unlike studies so far reported, where the PCE enhancement was correlated only qualitatively to CNT doping, our study (i) provides a novel and reversible path to tune and considerably enhance the cell efficiency by a few ppm gas exposure, and (ii) shows computational results that quantitatively relate the observed effects to the electrostatics of the cell through a systematic calculation of the work function. These effects have been cross-checked by exposing the cell to reducing molecules (i.e·NH3) that resulted to be detrimental to the cell efficiency, consistently with the theoretical ab-initio calculations.

Surface-defect passivation through complexation with organic molecules leads to enhanced power conversion efficiency and long term stability of perovskite photovoltaics

Surface-defect passivation through complexation with organic molecules leads to enhanced power conversion efficiency and long term stability of perovskite photovoltaics

Dimensionality-Controlled Surface Passivation for Enhancing Performance and Stability of Perovskite Solar Cells via Triethylenetetramine Vapor.

Perovskite solar cells (PSCs) have achieved unprecedented progress in terms of enhancement of power conversion efficiency (PCE). Nevertheless, device stability is still an obstacle to the commercialization of this emerging photovoltaic technology. Though strategies such as compositional management and ligand engineering have been reported to tackle this critical issue, these methods often have drawbacks such as compromised device performance. Herein, we propose an approach combining material dimensionality control and interfacial passivation by a post-device treatment via triethylenetetramine (TETA) vapor to enhance both efficiency and stability of Cs0.05FA0.79MA0.16PbI2.5Br0.5-based PSCs. Results of X-ray diffraction and scanning electron microscopy show the formation of low-dimensional perovskites at the interface between the perovskite film and the hole transporting layer after the TETA vapor treatment. Measurements of the energy level alignment and electrochemical properties by ultraviolet photoelectron spectroscopy and impedance spectra confirm the reduced density of trap states and improved interfacial charge transport. Consequently, TETA-based treatment significantly enhances both efficiency (from 17.07 to 18.03%) and stability (PCE retention from 73.4 to 88.9%) of the PSCs under >65% relative humidity for 1000 h compared to the controlled device without TETA treatment. Furthermore, the TETA vapor also shows an advantageous effect of dramatically improving the performance of PSC devices, which initially had poor performance (from 6.8 to 10.5%) through surface defect passivation.