Jsc Enhancement Research Articles

Intraband transitions at a CsPbBr3/GaAs heterointerface in a two-step photon upconversion solar cell

Two-step photon upconversion solar cells (TPU-SCs) based on III–V semiconductors can achieve enhanced sub-bandgap photon absorption because of intraband transitions at the heterointerface. From a technological aspect, the question arose whether similar intraband transitions can be realized by using perovskite/III–V semiconductor heterointerfaces. In this article, we demonstrate a TPU-SC based on a CsPbBr3/GaAs heterointerface. Such a solar cell can ideally achieve an energy conversion efficiency of 48.5% under 1-sun illumination. This is 2.1% higher than the theoretical efficiency of an Al0.3Ga0.7As/GaAs-based TPU-SC. Experimental results of the CsPbBr3/GaAs-based TPU-SC show that both the short-circuit current JSC and the open-circuit voltage VOC increase with additional illumination of sub-bandgap photons. We analyze the excitation power dependence of JSC for different excitation conditions to discuss the mechanisms behind the enhancement. In addition, the observed voltage-boost clarifies that the JSC enhancement is caused by an adiabatic optical process at the CsPbBr3/GaAs heterointerface, where sub-bandgap photons efficiently pump the electrons accumulated at the heterointerface to the conduction band of CsPbBr3. Besides the exceptional optoelectronic properties of CsPbBr3 and GaAs, the availability of a CsPbBr3/GaAs heterointerface for two-step photon upconversion paves the way for the development of high-efficiency perovskite/III–V semiconductor-based single-junction solar cells.

Novel Polyelectrolytes Based on Naphthalene Diimide with Different Counteranions for Cathode Interlayers in Polymer Solar Cells.

We synthesized novel polyelectrolytes based on naphthalene diimide with quaternary amine featuring hydroxyl groups at the side chain, along with different counteranions (PF-NDIN-Br-OH and PF-NDIN-I-OH) for polymer solar cell (PSC) application as the interlayer. The polyelectrolytes establish a beneficial interface dipole through the ionic moieties and synergistic effects arising from the hydroxyl groups located at the side chain. Incorporating polyelectrolytes as the cathode interlayer resulted in an enhancement of the power conversion efficiency (PCE). The PCE of the device with PF-NDIN-Br-OH increased from 8.96% to 9.51% compared to the ZnO-only device. The best PCE was obtained with the device based on PF-NDIN-I-OH, up to 9.59% resulting from the Jsc enhancement. This outcome implies a correlation between the performance of the device and the synergistic effects observed in polyelectrolytes containing hydroxyl groups in the side chain, along with larger anions when employed in PSCs.

Microstructures and photovoltaic effect of KNbO3–SrCo0.5Hf0.5O3−δ ferroelectric semiconductors

AbstractPolarization is one of the unique properties of ferroelectric materials; yet the polarization mechanism for enhancing ferroelectric photovoltaic performance is rarely been investigated, particularly in terms of bandgap variation. In this work, the effect of high‐field polarization on the enhanced photovoltaic performance of a ferroelectric ceramic, 0.98KNbO3–0.02SrCo0.5Hf0.5O3−δ (KNSCH2), was explored in terms of bandgap variation. The bandgap of the KNSCH2 sample shrank after polarization because of the increase in potential energy band overlap and the upward shift of the valence band due to increased oxygen‐vacancy defects. The polarization optimized the energy band structure of KNSCH2, promoting the separation and transport of photoinduced carriers and thus further enhancing its photovoltaic performance. The KNSCH2 sample shows a twofold enhancement in Jsc after 60 kV/cm polarization. The degree of the lattice distortion of KNSNH2 increased following polarization, causing a minute increase in its cell asymmetry. The reasons for the bandgap narrowing and the creation of sub‐bandgaps in the KNSCH samples were also investigated. This work opened new doors to understanding the mechanisms underlying the polarization‐enhanced photovoltaic performance of ferroelectric materials.

Plasmonic enhancement of photovoltaic characteristics of organic solar cells by employing parabola nanostructures at the back of the solar cell.

In this paper, we demonstrate the enhanced performance of organic solar cells (OSCs) comprising low band gap photoactive layers (PMDPP3T:PC70BM) and 2-dimensional (2D) arrays of either Ag nano-spheres, nano-hemispheres, or nano-parabolas embedded at the back of the OSCs. Finite-difference time-domain (FDTD) simulations were performed to compare the performance of the OSCs containing the different plasmonic nanostructures, in terms of optical absorption, short circuit current density (JSC) and power conversion efficiency (PCE). The results demonstrate that single junction OSCs consisting of this new active layer polymer (PMDPP3T), blended with PC70BM, and plasmonic nanostructures at the back of the OSC can enhance the optical absorption in the visible and the NIR region. We demonstrate that the aspect ratio of the nanoparticles embedded at the back of OSCs is a vital parameter for light absorption enhancement. It is observed that the performance in terms of JSC and PCE enhancement of OSC having 2D arrays of Ag nano-parabola at the back of the solar cell improved by 26.41% and 26.37%, respectively, compared to a planar OSC. The enhancement in photon absorption can be attributed due to the enhancement of light scattering from metallic nanostructures near their localized plasmon resonance.

Molecular design and synthesis of acetohydrazonoyl cyanide structures as efficient dye-sensitized solar cells with enhancement of the performance of the standard N-719 dye upon co-sensitization

Four novel acetohydrazonoyl cyanide compounds (5–8) with a triphenylamine moiety as an electron donor for use in dye-sensitized solar cells (DSSCs) have been designed and synthesized. The target molecules and their intermediates were well characterized using various spectral techniques. Their absorption spectra and electrochemical and photovoltaic properties are extensively investigated and compared with N-719 dye. The photovoltaic efficiency of these new dyes under AM1.5 ranges from 1.91% to 5.17% without the use of any additive. Compound 8 achieved the highest photovoltaic conversion efficiency (PCE, η = 5.17%) among the existing dyes due to the high values of the photocurrent (JSC = 13.66 mA cm−2) and photovoltage (VOC = 647 mV). Due to the good results shown by compound 8, the compound was used as a co-sensitizer along with the N-719 dye to improve its properties and raise its efficiency. The results showed that using (0.2 mM of compound 8 + 0.2 mM of N-719) improved the performance of the fabricated cell (PCE, η = 8.63%) with the enhancement in both VOC (682 mV) and JSC (20.39 mA cm−2) compared to the cell fabricated with N-719 alone (PCE, η = 6.23%, VOC = 623 mV, JSC = 16.48 mA cm−2). Furthermore, electronic excitations simulated using time-dependent DFT agreed well with experimentally obtained sensitizer results, indicating that the exchange-correlation function and basis set used to predict the spectra of the co-sensitizers are quite appropriate for the calculations. In conclusion, the results showed the potential of simple organic co-sensitizers in the development of efficient DSSCs.

Thermal Activation of PEDOT:PSS/PM6:Y7 Based Films Leads to Unprecedent High Short‐Circuit Current Density in Nonfullerene Organic Photovoltaics

AbstractFinding an effective approach to suppress trap formation is a potential route for enhancing the performance of nonfullerene organic photovoltaic (NF‐OPVs) devices. Here, an extraordinary short‐circuit current density (JSC) value of 32.65 mA cm‐2 is achieved, higher than the state‐of‐the art NF‐OPVs reported, reaching a high power conversion efficiency (PCE) of 17.92%. This remarkable enhancement is exhibited through the fine‐tuning of PEDOT:PSS/PM6:Y7 films and interface morphologies via applying the prethermal treatment approach (Pre‐TT) to the devices, which exhibit JSC and PCE enhancement of 21% and 8%, respectively, compared to the pristine devices. Accordingly, the dependence of the JSC upon the Pre‐TT approach through a range of morphological, optical, electrical, and advanced transient measurements is investigated. The Pre‐TT‐based films are found to possess optimal smooth blend morphology with better dispersity owing to reduced domain size. Moreover, the measurements show that the optimized treated devices present higher exciton dissociation probabilities and generation rate of the free charge carriers, showing an ideal balanced electron/hole mobility that reveals the JSC and PCE enhancement. Hence, Pre‐TT approach provides a facile passivation strategy that reduces the trap state density of the blend film, improves interface charge transfer, allows balanced electron/hole mobility, and thus promotes device performance.

Plasmon induced quantified agglomeration of SiO2 nanoparticles to improve in efficiency in solar cell

The impact of plasmonic confinement induced by the SiO2 nanosphere utilized as a photonic absorber in a solar cell is investigated in this paper. The modified Stober technique is utilized for irradiation experiments using the size and shape of colloidal silica nanoparticles at two dosages of 0.485mg/ml and 0.693mg/ml solutions. The agglomerated silica is placed as an absorbent layer on a solar cell, and the J-V characteristics are studied under solar irradiation. The enhancement in efficiency and Jsc is far greater than predicted induced in photon injection caused by silica nanoparticle coating under coverage limit.

Sequential Passivation for Lead‐Free Tin Perovskite Solar Cells with High Efficiency

AbstractLead‐free tin perovskite solar cells (PKSCs) have attracted tremendous interest as a replacement for toxic lead‐based PKSCs. Nevertheless, the efficiency is significantly low due to the rough surface morphology and high number of defects, which are caused by the fast crystallization and easy oxidization. In this study, a facile and universal posttreatment strategy of sequential passivation with acetylacetone (ACAC) and ethylenediamine (EDA) is proposed. The results show that ACAC can reduce the trap density and enlarge the grain size (short‐circuit current (Jsc) enhancement), while EDA can bond the undercoordinated tin and regulate the energy level (open‐circuit voltage (Voc) enhancement). A promising 13 % efficiency is achieved with better stability. In addition, other combinations of diketones or amines are selected, with similar effects. This study provides a universal strategy to enhance the crystallinity and passivate defects while fabricating stable PKSCs with high efficiency.

Effect of counter anions and side-chain modification of conjugated polymers for organic solar cells as an interlayer: An in-depth investigation of the diverse modification of ionic functionality

A conjugated polymer based on dimethylaminopropyl fluorene and naphthalene diimide (PFN-NDI) was synthesized to apply for organic solar cells (OSC) as the interlayer. Further, we convert the amine group to quaternary ammonium salt with various types of counter anion (CA) such as bromide and iodide, in addition to the side chain modification with hydroxyl groups. These materials generate a favorable interface dipole by the ionic functionality at the end of the side chain, while the polar hydroxyl groups increase the magnitude of interface dipole. The power conversion efficiency (PCE) was improved by incorporating polyelectrolytes as the interlayer. The PCE of the device based on PFN-NDI with acetic acid additive as the interlayer was enhanced over the device with pristine ZnO from 8.40% to 8.51%. The PCE of the device based on PFN-NDI-Br was enhanced up to 9.02%, due to the significant improvement of FF. The incorporation of extra hydroxyl groups increases the PCE up to 9.15% as a result of the synergy effect in the interface dipole moment. Furthermore, the PCE improvement was obtained by using PFN-NDI-I as the interlayer, up to 9.41%, which is mainly resulted from the Jsc enhancement. This result suggests a correlation between device performance and ionic functionality modification.

Performance enhancement of CIGS solar cells using ITO as buffer layer

The purpose of this research is the reduction of parasitic absorption to improve the CIGS solar cell performance. Decreasing the traditional CdS buffer layer thickness is a reduction method for parasitic absorption which yields to a higher photocurrent. However, degradation of the open-circuit voltage (Voc) and fill factor (FF) are observed in J-V measurements as a thin (<30 nm) CdS buffer layer is applied. Moreover, the toxic CdS has a relatively low bandgap which tends to a significant parasitic absorption in the blue wavelength region. Here, Indium Tin Oxide (ITO) with a larger bandgap is suggested as an alternative buffer layer, which unlike the CdS, demonstrates a significant efficiency enhancement without adversely affecting Voc and FF. ITO is an environmentally friendly substance which its ultra-thin thickness leads to a significant short-circuit current (Jsc) enhancement. Hence, an improvement of efficiency about 6% is achieved by successfully replacing the traditional CdS layer with ITO layer in conventional CIGS solar cell. Furthermore, ZnMgO (ZMO) with more transparency and larger bandgap, was applied to replace conventional ZnO window layer of the CIGS solar cell for further increment in Jsc. In addition, ZMO as a proper window layer in the proposed cell structure tends to the modification of J–V curve distortion at low temperatures. Ultimately, the final proposed structure with the alternative window layer (Mo/CIGS/ITO/ZMO/AZO) exhibited 7.5% efficiency improvement in comparison with the conventional solar cells.

Photovoltaic Performance of Dye-Sensitized Solar Cells with a Solid-State Redox Mediator Based on an Ionic Liquid and Hole-Transporting Triphenylamine Compound

An ionic liquid, 1-methyl-3-propylimidazolium iodide (MPII), was solidified with an organic hole-transporting material, 4,4′,4″-tris[(3-methylphenyl)phenylamino]triphenylamine (m-MTDATA), and the resulting solid-state redox mediator (RM) (m-MTDATA-solidified MPII) was employed in solar devices to realize solid-state dye-sensitized solar cells (sDSSCs). Solar devices with only MPII or m-MTDATA as an RM showed almost 0 mA/cm2 of short-circuit current (Jsc) and thus 0% power conversion efficiency (PCE). However, an sDSSC with the m-MTDATA-solidified MPII exhibited 4.61 mA/cm2 of Jsc and 1.80% PCE. It was found that the increased Jsc and PCE were due to the formation of I3−, which resulted from a reaction between the iodie (I−) of MPII and m-MTDATA cation. Further enhancement in both Jsc (9.43 mA/cm2) and PCE (4.20%) was observed in an sDSSC with 4-tert butylpyridine (TBP) as well as with m-MTDATA-solidified MPII. We attributed the significant increase (about 230%) in PCE to the lowered diffusion resistance of I−/I3− ions in the solid-state RM composed of the m-MTDATA-solidified MPII and TBP, arising from TBP’s role as a plasticizer.

A comprehensive investigation of the potential of metal assisted chemical etched (MACE) nano-textures over conventional micron-sized iso-textures for industrial silicon solar cell applications

We present a comprehensive comparative analysis of acid textured and MACE (Metal Assisted Chemical Etching) nano-textured multi crystalline silicon (mc-Si) solar cells processed in an industrial cell line in terms of performance parameters. The batch average open circuit voltage of nano-textured solar cells was marginally lower and the measures for improving the same are discussed. Batch average short circuit current (JSC) and fill factor (FF) were respectively 0.65 mA-cm−2 and 0.7% (absolute) higher for MACE nano-textured solar cells. Significantly lower surface reflectance in MACE nano-textured cells in the blue and near infrared regions are found to be the reason for the enhancement in JSC. The main component of FF gain is identified as the lower series resistance in MACE cells. The contact formation mechanism in screen printed mc-Si solar cells, investigated using scanning electron microscopy, revealed that the elevated portions at the boundaries of the textures act as favorable sites for silver crystallite precipitation. A larger areal density of such sites is observed on the MACE nano-textured surface than in case of acid textured solar cells, leading to a much lower series resistance. The results suggest the potential for the application of MACE in the more popular mono-crystalline silicon cell technology for further reduction of contact resistance. Alternatively, MACE may be used to obtain similar contact resistance with lower amount of silver paste, compared to iso- and pyramid textured solar cells.

Improvement in photovoltaic efficiency of solar cells with ZnO nanorods and electrophoretically-adsorbed dyes

ZnO nanorods grown on the F-doped tin oxide glass by a chemical bath deposition were sensitized by the electrophoretic technique or the conventional soaking method, and the resulting electrodes were applied to photoanodes of dye-sensitized solar cells (DSSCs). The DSSC with an electrophoretically-sensitized ZnO layer showed an increase in both the short-circuit current (Jsc ) and the open-circuit voltage (Voc ), resulting in a 220% enhancement of photovoltaic performance, when compared to that of the reference cell with a conventionally-sensitized ZnO layer. By applying the electrophoresis to dye adsorption, dye-loading amount was considerably increased, and thereby enhancing the light harvesting efficiency and reducing the interfacial charge recombination between photoinjected electrons and I3 −. This led to the enhancement in Jsc and Voc , compared to those of the reference cell.

Fluorinated Zinc and Copper Phthalocyanines as Efficient Third Components in Ternary Bulk Heterojunction Solar Cells.

Fluorinated zinc and copper metallophthalocyanines MPcF48 are synthesized and incorporated as third component small molecules in ternary organic solar cells (TOSCs). To enable the high performance of TOSCs, maximizing short-circuit current density (J SC) is crucial. Ternary bulk heterojunction blends, consisting of a polymer donor PTB7-Th, fullerene acceptors PC70BM, and a third component MPcF48, are formulated to fabricate TOSCs with a device architecture of ITO/PFN/active layer/V2O5/Ag. Employing copper as metal atom substitution in the third component of TOSCs enhances J SC as a result of complementary absorption spectra in the near-infrared region. In combination with J SC enhancement, suppressed charge recombination, improved exciton dissociation and charge carrier collection efficiency, and better morphology lead to a slightly improved fill factor (FF), resulting in a 7% enhancement of PCE than those of binary OSCs. In addition to the increased PCE, the photostability of TOSCs has also been improved by the appropriate addition of CuPcF48. Detailed studies imply that metal atom substitution in phthalocyanines is an effective way to improve J SC, FF, and thus the performance and photostability of TOSCs.

Alkali metal cation incorporated Ag3BiI6 absorbers for efficient and stable rudorffite solar cells

Abstract Toxic lead and poor stability are the main obstacles of perovskite solar cells. Lead-free silver bismuth iodide (SBI) was first attempted as solar cells photovoltaic materials in 2016. However, the short-circuit current of the SBI rudorffite materials is commonly &amp;lt;10 mA/cm2, limiting the overall photovoltaic performance. Here, we present a chemical composition engineering to enhance the photovoltaic performance. In this study, we incorporated a series of alkali metal cations (Li+, Na+, K+, Rb+ and Cs+) into Ag3BiI6 absorbers to investigate the effects on the photovoltaic performance of rudorffite solar cells. Cs+ doping improved VOC and Na+ doping showed an obvious enhancement in JSC. Therefore, we co-doped Na+ and Cs+ into SBI (Na/Cs-SBI) as the absorber and investigated the crystal structure, surface morphology and optical properties. The photo-assisted Kelvin probe force microscopy was used to measure surface potential and verified that Na/Cs doping could reduce the electron trapping at the grain boundary and facilitate electron transportation. Na/Cs-SBI reduced the electron–holes pairs recombination and promoted the carrier transport of rudorffite solar cells. Finally, the Na/Cs-SBI rudorffite solar cell not only exhibited a power conversion efficiency (PCE) of 2.50%, a 46% increase to the SBI device (PCE = 1.71%), but also was stable in ambient conditions for &amp;gt;6 months.

Ultrafast Charge Generation Enhancement in Nanoscale Polymer Solar Cells with DIO Additive.

We study the ultrafast photoexcitation dynamics in PBDTTT-C-T (P51, poly(4,8-bis(5-(2-ethylhexyl)-thiophene-2-yl)-benzo[1,2-b:4,5-b′]dithiophene-alt-alkylcarbonyl-thieno[3,4-b]thiophene)) film (~100 nm thickness) and PBDTTT-C-T:PC71BM (P51:PC71BM, phenyl-C71-butyric-acid-methyl ester) nanostructured blend (∼100 nm thickness) with/without DIO(1,8-diiodooctane) additives with sub-10 fs transient absorption (TA). It is revealed that hot-exciton dissociation and vibrational relaxation could occur in P51 with a lifetime of ~160 fs and was hardly affected by DIO. However, the introduction of DIO in P51 brings a longer lifetime of polaron pairs, which could make a contribution to photocarrier generation. In P51:PC71BM nanostructured blends, DIO could promote the Charge Transfer (CT) excitons and free charges generation with a ~5% increasement in ~100 fs. Moreover, the dissociation of CT excitons is faster with DIO, showing a ~5% growth within 1 ps. The promotion of CT excitons and free charge generation by DIO additive is closely related with active layer nanomorphology, accounting for Jsc enhancement. These results reveal the effect of DIO on carrier generation and separation, providing an effective route to improve the efficiency of nanoscale polymer solar cells.

Optical Properties of CaF2 Thin Film Deposited on Borosilicate Glass and Its Electrical Performance in PV Module Applications

Calcium fluoride (CaF2) is deposited via vacuum thermal evaporation on borosilicate glass to produce an anti-reflection coating for use in solar modules. Macleod’s essential simulation is used to optimize the thickness of the CaF2 coating on the glass. Experimentally, a 120 ± 4 nm-thin CaF2 film on glass shows an average increase of ~4% in transmittance and a decrease of ~3.2% in reflectance, respectively, when compared to that of uncoated glass (Un CG), within the wavelength spectrum of approximately 350 to 1100 nm. The electrical PV performance of CaF2-coated glass (CaF2-CG) was analyzed for conventional and lightweight photovoltaic module applications. An improvement in the short-circuit current (Jsc) from 38.13 to 39.07 mA/cm2 and an increase of 2.40% in the efficiency (η) was obtained when CaF2-CG glass was used instead of Un CG in a conventional module. Furthermore, Jsc enhancement from 35.63 to 36.44 mA/cm2 and η improvement of 2.32% was observed when a very thin CaF2-CG was placed between the polymethyl methacrylate (PMMA) and solar cell in a lightweight module.

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.

Concurrent improvement in JSC and VOC in high-efficiency ternary organic solar cells enabled by a red-absorbing small-molecule acceptor with a high LUMO level

The ternary device achieved an excellent PCE of 15.02% with enhancement in both VOC and JSC by adding a red-absorbing SMA with a high LUMO level.

Optical Tunneling Mediated Sub-Skin-Depth High Emissivity Tungsten Radiators.

Tailoring the spectrum of thermal radiation at high temperatures is a central issue in the study of thermal radiation harnessed energy resources. Although bulk metals with periodic cavities incorporated into their surfaces provide high emissivity, they require a complicated micron metal etch, thereby precluding reliable, continuous operation. Here, we report thermally stable, highly emissive, ultrathin (<20 nm) tungsten (W) radiators that were prepared in a scalable and cost-effective route. Alumina/W/alumina multiwalled, submicron cavity arrays were fabricated sequentially using nanoimprinting lithography, thin film deposition, and calcination processes. To highlight the practical importance of high-temperature radiators, we developed a thermophotovoltaic (TPV) system equipped with fabricated W radiators and low-bandgap GaSb photovoltaic cells. The TPV system produced electric power reliably during repeated temperature cycling between 500 and 1200 K; the power density at 1200 K was fixed to be approximately 1.0 W/cm2. The temperature-dependent electric power was quantitatively reproduced using a one-dimensional energy conversion model. The symmetric configuration of alumina/W/alumina multiwall together with the presence of a void inside each cavity alleviated thermal stress, which was responsible for the stable TPV performance. The short-current-density (JSC) of developed TPV system was augmented significantly by decreasing the W thickness below its skin depth. A 17 nm thick W radiator yielded a 32% enhancement in JSC compared to a 123 nm thick W radiator. Electromagnetic analysis indicated that subskin-depth W cavity arrays led to suppressed surface reflection due to the mitigated screening effect of free electrons, thereby enhancing the absorption of light within each W wall. Such optical tunneling-mediated absorption or radiation was valid for any metal material and morphology (e.g., planar or patterned).