Fill Factor Of Cells Research Articles

Series Resistance Measurements of Perovskite Solar Cells Using Jsc–Voc Measurements

The fill factor (FF) of perovskite solar cells is considerably lower than that of gallium arsenide and silicon cells, though they have similar open‐circuit voltage deficits. To probe the FF loss, which mainly comes from series resistance, the Jsc–Voc characterization technique is applied to perovskite solar cells. A continuous‐lamp solar simulator with an array of neutral density filters is used instead of the quasi‐steady‐state photoconductance technique commonly employed for silicon cells, which allows us to tune sweep parameters to accommodate the complex behavior of perovskites such as hysteresis. It is found that, for Cs0.25FA0.75Pb(Br0.2I0.8)3 (CsFA) perovskite cells, sweeping from positive to negative voltage yields the same series resistance regardless of sweep speed, whereas this is not the case if the sweep is reversed. However, for CH3NH3PbI3 perovskite cells, the series resistance is independent of the sweep speed in both sweep directions. It is also found that, for a poly[bis(4‐phenyl)(2,4,6‐trimethylphenyl)amine] (PTAA) hole contact, increasing the PTAA thickness barely changes the recombination‐limited pseudo‐FF, but reduces the FF due to increased series resistance. A maximum FF of 80.9% was achieved with the PTAA hole contact on a CsFA perovskite absorber.

Impact of Bimolecular Recombination on the Fill Factor of Fullerene and Nonfullerene-Based Solar Cells: A Comparative Study of Charge Generation and Extraction

Power conversion efficiencies of donor/acceptor organic solar cells utilizing nonfullerene acceptors have now increased beyond the record of their fullerene-based counterparts. There remain many fu...

Semi-transparent photovoltaics using ultra-thin Cu(In,Ga)Se2 absorber layers prepared by single-stage co-evaporation

Semi-transparent thin-film solar cells with ultra-thin Cu(In,Ga)Se2 (CIGS) absorber layers were fabricated on fluorine-doped tin oxide coated glass substrates using a single-stage co-evaporation process. The effects of the deposition conditions, such as the absorber thickness, deposition temperature, and post-deposition treatment using NaF on the material properties of the CIGS films were evaluated. In addition, the power conversion efficiency (PCE) and average visible transmission (AVT) in the wavelength range of 420–720 nm for semi-transparent CIGS solar cells using these absorber layers were systematically investigated. The AVT of the solar cells was directly dependent on the thickness of the CIGS absorber films. When the film thickness of the absorber layers increased from 300 nm to 950 nm, the AVT decreased gradually from 9.04% to 0.30%, while their PCE values did not show a clear dependence on the absorber thickness. Narrow columnar grains were observed in the microstructure of the ultra-thin CIGS absorber layers, irrespective of the film thickness and deposition temperature. Doping the ultra-thin CIGS absorber layers with Na after film deposition enhanced solar cell performance (the open circuit voltage (VOC) and fill factor (FF) were improved). The enhanced cell performance was attributed to the lack of a resistive GaOx film at the CIGS/FTO interface and thermal damage to the FTO back contact. The PCE values of semi-transparent solar cells with ultra-thin CIGS absorber layers prepared under the optimal deposition conditions varied from 6.46% to 9.78% when the CIGS absorber thickness was varied from 200 nm to 300 nm, respectively, while the corresponding AVT values changed from 18.59% to 9.04%.

Silicon Photomultipliers: Technology Optimizations for Ultraviolet, Visible and Near-Infrared Range

Silicon photomultipliers (SiPMs) are single-photon sensitive solid-state detectors that are becoming popular for several applications, thanks to massive performance improvements over the last years. Starting as a replacement for the photomultiplier tube (PMT), they are now used in medical applications, big high-energy physics experiments, nuclear physics experiments, spectroscopy, biology and light detection and ranging (LIDAR) applications. Due to different requirements in terms of detection efficiency, noise, etc., several optimizations have been introduced by the manufacturers; for example, spectral sensitivity has been optimized for visible light, near ultraviolet, vacuum ultraviolet, and near infrared light. Each one of them require specific processes and structural optimization. We present in this paper recent improvements in SiPM performance, owing to a higher cell fill-factor, lower noise, improved silicon materials, and deep trench isolation. We describe issues related to the characterization of analog SiPM, particularly due to the different sources of correlated noise, which have to be distinguished from each other and from the primary pulses. We also describe particular analyses and optimizations conducted for specific applications like the readout of liquid noble gas scintillators, requiring these detectors to operate at cryogenic temperatures.

Overcoming intrinsic defects of the hole transport layer with optimized carbon nanorods for perovskite solar cells.

To overcome the intrinsic chemical-reduction-activity of highly p-doped PEDOT:PSS and improve the open-circuit voltage (Voc) of planar inverted perovskite solar cells, a kind of oxidized carbon nanorods (OCNRs) is developed by a ball-milling/chemical-oxidation method and incorporated into PEDOT:PSS hole transport layer (HTL). The incorporation of OCNRs can increase the work function of the PEDOT:PSS layer, which avoids the energy-level mismatch between the PEDOT:PSS HTL and the HOMO level of the CH3NH3PbI3 perovskite layer, leading to a relatively high Voc of 1.01 V (vs. 0.92 V for the PEDOT:PSS device). Moreover, the introduction of OCNRs into the PEDOT:PSS HTL increases the grain size and uniformity of the perovskite layer, accompanied by the improved charge transport ability. As a result, the fill factor of perovskite solar cells is increased from 75.4% to 81.7%, and the best power conversion efficiency of 19.02% is achieved.

Study on Photoelectrochemical Properties of Ternary Doped Cd1-xZnxS thin Film Deposited by Chemical Bath Deposition

The photoelectrochemical properties of Cd1-xZnxS (x = 0, 0.2, 0.4, 0.6, 0.8, and 1) thin film, prepared by Chemical bath deposition technique on simple glass and fluorine doped tin oxide(FTO) coated glass substrate were studied. The X-ray diffraction (XRD) studies indicate that film was hexagonal with polycrystalline in nature. The current-voltage (I-V) curve for PEC cell of configuration n-Cd1-xZnxS//1M polysulphide//C under illumination for film deposited on FTO coated glass substrate, respectively. I-V curve characterizes the semiconductor/electrolyte junction which acts like a diode. The interface shows a rectifying behavior with a cathodic current (direct) much greater than the anodic current (reverse), which is typical of a Schottky junction formed between an n-type semiconducting material and a metal or an electrolyte. Various PEC parameters such as the junction ideality factor under illumination, series and shunt resistances, efficiency and, fill factor have been calculated for the PEC cells formed. The efficiency and fill factor of these PEC cells are found to be increased as increasing X=0.4 and further, it decreases as X increases.

Construction of Schottky junction solar cell using silicon nanowires and multi-layered graphene

Schottky junction solar cells based on n-type silicon nanowires (SiNWs) and multi-layered graphene were assembled. The textured substrates enhanced the light-harvesting compared to the planar substrates. Multi-layered graphene films produced by chemical vapor deposition and layer-by-layer stacking mitigated damages and increased the work function of graphene. Thus, both the power conversion efficiency and fill factor of Schottky junction solar cells could be improved with multi-layered graphene. It was found in the present study that the optimum photovoltaics performance of solar cells was achieved when double-layered graphene was used. The performance degraded with the number of graphene layers when it was more than 2 layers. While damages could be mitigated and the work function could be improved using multi-layered graphene in SiNWs Schottky junction solar cells, the optical transmittance of graphene would be reduced with excessive number of graphene layers.

High fill factor over 82% enabled by a biguanide doping electron transporting layer in planar perovskite solar cells

N-type doping in electron transport materials is an effective way to improve the electron collection and enhance the performance of the perovskite solar cells (PSCs). Here, for the first time, an antibiotic and antimicrobial compound of 1-(o-Tolyl) biguanide (oTb) is used to dope the electron transport material of phenyl-C61-butyric acid methyl ester (PCBM). The oTb doping into the PCBM can increase the conductivity and reduce the work function of the PCBM. The oTb doping can significantly enhance the fill factor (FF) of the perovskite solar cells with the structure of glass/ITO/NiOx/MAPbI3/(oTb)PCBM/(PEIE)/Ag. For the cells without PEIE (polyethylenimine ethoxylated) coating, the oTb doping increases the FF from 0.57 to 0.73. S-shaped of the current density-voltage (J-V) characteristic under illumination is removed after the oTb doping. For the cells with PEIE coating between the (oTb)PCBM and Ag, the oTb doping increases the FF from 0.70 to 0.82. These results show the potential of the oTb as an n-dopant in the applications of perovskite solar cells.

Adaption of Basic Metal–Insulator–Semiconductor (MIS) Theory for Passivating Contacts Within Numerical Solar Cell Modeling

The main goal of a solar cell's contact is to simultaneously minimize the contact resistivity ρ cont and the effective recombination, the latter often expressed via J0, cont. To model the resulting solar cell characteristics, the simplest approach is to use those two measurable quantities as an effective boundary condition. Within crystalline silicon solar cell modeling, this “lumped” modeling approach is well valid for classical contacts, which feature high doping near the surface. Contacts to lowly doped silicon in contrast require a suitable stack of materials deposited onto the absorber surface to simultaneously induce band bending via an electrical barrier (field-effect passivation), provide chemical passivation, and efficiently extract majority carriers. Such “passivating contacts” often show effects not reproducible by the lumped modeling approach, e.g., non-ohmic contact resistivity, injection-dependent recombination, and voltage drops independent of current extraction. In this paper, we explore the suitability of the basic metal–insulator–semiconductor theory, employed as a boundary condition to a numerical model of the semiconductor transport in the absorber, to represent such effects of passivating contacts. We show that with only very few input parameters, several relevant experimental observations can be quantitatively replicated: temperature dependence of the fill factor of solar cells featuring tunnel-oxide passivating contacts, as well as implied versus external open-circuit voltage losses for heterojunction solar cells. While being the focus of this paper, the presented approach is well applicable also beyond crystalline silicon cells.

Thermal effect on CZTS solar cells in different process of ZnO/ITO window layer fabrication

In this work, a window layer consisting of zinc oxide (ZnO) and indium‑tin-oxide (ITO) thin films was prepared by sputtering under different heat treatment processes (in-situ or post annealing) to study the effect on structural ordering and performance of Cu2ZnSnS4 (CZTS) solar cells. It is found that all characteristic performance parameters including open circuit voltage (Voc), short circuit current density (Jsc), fill factor (FF) and efficiency of CZTS solar cells were improved for the window layer with ITO thickness = 350 nm post-annealed at lower temperature. Specifically, Voc of the CZTS device was increased by 57 mV when the window layer was post-annealed at 200 °C (Voc = 585 mV) compared to the device with window layer made at 300 °C (Voc = 528 mV). We further reduced the thickness of the window layer with ITO thickness = 140 nm which was deposited in an in-situ annealing process at 220 °C. Compared to the 350 nm thick film made by post-annealing, it is found that the thin film made by in-situ annealing help to further boost the Voc (equals 635 mV) and thus efficiency (3.20%) of CZTS solar cells. Study of the evolution of full width half maximum (FWHM) and intensity ratio (Q) of major Raman scattering peaks of CZTS indicates a much reduced structure disorder in the CZTS material with ZnO/ITO window layer annealed at low temperature. Further analysis of the evolution of diode ideality factor (A), reverse saturation current density (J0) and Urbach energy (Eu) of these devices revealed that the quality of bulk CZTS and/or CZTS/CdS heterojunction were more degraded at higher temperature. However, the in-situ annealing provided extra benefits to device performance which is possibly due to modification of interfacial properties of CZTS/CdS and/or CdS/ZnO.

Ohmic transition at contacts key to maximizing fill factor and performance of organic solar cells

While thermodynamic detailed balance limits the maximum power conversion efficiency of a solar cell, the quality of its contacts can further limit the actual efficiency. The criteria for good contacts to organic semiconductors, however, are not well understood. Here, by tuning the work function of poly(3,4-ethylenedioxythiophene) hole collection layers in fine steps across the Fermi-level pinning threshold of the model photoactive layer, poly(3-hexylthiophene):phenyl-C61-butyrate methyl ester, in organic solar cells, we obtain direct evidence for a non-ohmic to ohmic transition at the hole contact that lies 0.3 eV beyond its Fermi-level pinning transition. This second transition corresponds to reduction of the photocurrent extraction resistance below the bulk resistance of the cell. Current detailed balance analysis reveals that this extraction resistance is the counterpart of injection resistance, and the measured characteristics are manifestations of charge carrier hopping across the interface. Achieving ohmic transition at both contacts is key to maximizing fill factor without compromising open-circuit voltage nor short-circuit current of the solar cell.

Comparative performance of CdS/CdTe thin film solar cells fabricated with electrochemically deposited CdTe from 2-electrode and 3-electrode set-ups

A comparative study of the performance of glass/FTO/CdS/CdTe/Au thin film solar cells was carried out for solar cells fabricated with CdTe electrochemically grown using 2-electrode and 3-electrode set-ups. Structural, optical and morphological characterization of the CdTe films prior to solar cell fabrication show that both electrode set-ups produce CdTe with similar X-ray diffraction patterns, optical absorption properties and surface morphologies. Current density-voltage characterization of resulting solar cells also shows that CdTe from both electrode systems produced solar cells with comparable conversion efficiencies. The open-circuit voltage, short-circuit current density and fill factor of cells from both systems were in the ranges of (410–630) mV, (15.2–33.0) mAcm−2 and (0.32–0.49), respectively. These results indicate that the 2-electrode set-up can go a long way in reducing production cost by eliminating the reference electrode, which is also a potential impurity source, as well as ensuring a simplified deposition system.

Influence of selenization temperatures on the microstructures and photoelectric properties of iron-ion doped Cu(In,Ga)Se2 thin-film solar cells

Cu(In,Ga)Se2 (CIGS) thin films were prepared on molybdenum-coated flexible stainless steel substrates through a non-vacuumspin-coating process followed by selenization at temperatures ranging from 450 °C to 575 °C. The effects of selenization temperatures and concentration of iron ions on the photoelectric properties of the CIGS solar cells was thoroughly investigated. All X-ray diffraction (XRD) patterns appropriately matched with those of CIGS phase. The diffraction peak intensities of undoped CIGS films were increased with an increase in selenization temperatures. However, XRD peak intensities of iron-ion doped CIGS films were decreased with the elevation of selenization temperatures owing to the degradation of thermal stability of CIGS films after iron-ion doping. As the selenization temperatures increased, the grain sizes of particles in CIGS films increased, and the films became densified with flat surfaces. The values of Voc, Jsc, and fill factor for CIGS solar cells prepared at 450 °C were 0.401 V, 21.84 mA/cm2, and 41.12%, respectively. These parameters were enhanced with increasing selenization temperatures due to improved crystallinity of CIGS and densified microstructures. However, iron-ion doping deteriorated the photoelectric properties because iron ions diffused into the absorption layers at high temperatures. The present study indicates that iron-ion doping adversely affected the photoelectric performance and microstructures of CIGS solar cells.

Effect of Core Size on Performance of Fused-Ring Electron Acceptors

We report 4 fused-ring electron acceptors (FREAs) with the same end-groups and side-chains but different cores, whose sizes range from 5 to 11 fused rings. The core size has considerable effects on the electronic, optical, charge transport, morphological, and photovoltaic properties of the FREAs. Extending the core size leads to red-shift of absorption spectra, upshift of the energy levels, and enhancement of molecular packing and electron mobility. From 5 to 9 fused rings, the core size extension can simultaneously enhance open-circuit voltage (VOC), short-circuit current density (JSC), and fill factor (FF) of organic solar cells (OSCs). The best efficiency of the binary-blend devices increases from 5.6 to 11.7%, while the best efficiency of the ternary-blend devices increases from 6.3 to 12.6% as the acceptor core size extends.

Reduce the hysteresis effect with the PEIE interface dipole effect in the organic-inorganic hybrid perovskite CH3NH3PbI3-xClx solar cell

Abstract Power conversion efficiency (PCE) of CH3NH3PbI3 perovskite solar cells has been developed rapidly, it reached the 22.1%. However, the anomalous hysteresis found in I-V measurements can cause an inaccurate estimation of the efficiency. In this article, we fabricated the ITO/PEDOT:PSS/CH3NH3PbI3-xClx/ PCBM/PEIE/Al structure perovskite solar cell, we inserted an interface layer of Polyethylenimine ethoxylated (PEIE) into solar cell device between the PCBM and aluminum (Al) electrode, the electrical filed induce photoluminescence (PL) quenching experiment and capacitance-voltage characteristic both demonstrate that the PEIE layer exists an interface dipole effect in the perovskite solar cell device, it can effectively reduce the hysteresis effect in the I-V measurement, and greatly increase the solar cell's efficiency from the 10.93%–14.46%. Utilizing the photoinduction dielectric response technology, we further found that the interface dipole effect increased the built-in electrical field, and enhanced the charge carrier transport properties, consequently, increased the short-circuit current (Jsc). On the other hand, the interface dipole effect decreased the concentration of defect on the CH3NH3PbI3-xClx surface, and made the charge injection barrier to increasing at the electrode and perovskite interface, leading to enhance the open-circuit voltage (Voc). In addition, the diminution of defect could further increase more effective electron transport channels, leading to the more charge carriers transport toward to the corresponding electrode, and increased the solar cell's Fill Factor (FF). Therefore, the addition PEIE interface layer in the perovskite solar cell not only can remove the hysteresis effect but also develop the high PCE perovskite solar cell. We hope the interface dipole effect as an effective methods can greatly promote and develop high efficiency and stable perovskite solar cells.

Asymmetrical Small Molecule Acceptor Enabling Nonfullerene Polymer Solar Cell with Fill Factor Approaching 79%

Relative to the increase of open-circuit voltage and short-circuit current, promoting fill factor (FF) of the polymer solar cells (PSCs) seems to be more challenging. Here, we designed and synthesized two asymmetrical small molecule acceptors (IDT6CN-M and IDT8CN-M) with large dipole moments. We find that the strong intermolecular interaction and favorable antiparallel packing induced by the dipole moment can effectively enhance both lamellar packing and π–π stacking. The PSCs based on PBDB-T:IDT6CN-M and PBDB-T:IDT8CN-M achieved FFs of up to 76.1% and 78.9%, corresponding to PCEs of 11.23% and 12.43%, respectively. To the best of our knowledge, 78.9% FF is a new record for nonfullerene PSCs. Overall, our work provides a simple and effective molecule-designing method to promote FF of nonfullerene PSCs.

Designing ternary blend all-polymer solar cells with an efficiency of over 10% and a fill factor of 78%

In recent years, ternary blend bulk-heterojunction (BHJ) all-polymer solar cells have been gradually developed to better utilize the solar irradiance spectrum. However, power conversion efficiencies remain below 10%, mainly because of the low fill factor. Generally, the fill factor of all-polymer solar cells is limited mainly by the competition between the recombination and extraction of free charges. Here, we design advanced ternary blend all-polymer solar cells with a high fill factor of 78%, thus demonstrating how such recombination thresholds can be overcome. These results can be attributed to the high and balanced bulk charge mobility, reduced recombination, and optimized morphology, as well as the intimate mixing properties of the two donors in the photoactive layer.

Perovskite/p-Si photodiode with ultra-thin metal cathode

Perovskites have attracted great interest because they provide promising improvement for solar cells. Yet, the perovskites have not been extensively used by the researchers for diode applications. In this study, both Al/p-type Si and Al/perovskite/p-type Si devices have been obtained. We used a facile and cost-effective way of making perovskite thin film layer between the ultra-thin metal and semiconductor as an interfacial layer by spin coating technique as well distributed film. In order to keep costs low, aluminum was chosen as the cathode material. The Al/p-type Si and Al/perovskite/p-type Si devices have exhibited good rectifying properties and calculated rectifying ratio of the devices are 2.39 × 103 and 4.56 × 104 at 1 V, respectively. Photodiode properties of the device have been illustrated and discussed in the details by calculating some diode parameters. While the Al/p-type Si device has 1.53 ideality factor value and 0.72 eV barrier height, the ideality factor and barrier height values of Al/perovskite/p-type Si device have been obtained as 2.12 and 0.87 eV, respectively under dark condition. The solar cell efficiency and fill factor values of the Al/perovskite/p-type Si device are 7.44 × 10−3 and 23.7, respectively. Such devices can find applications as rectifiers and photodiodes in industry.

Functional graded fullerene derivatives for improving the fill factor and device stability of inverted-type perovskite solar cells

A graded fullerene derivative thin film was used as a dual-functional electron transport layer (ETL) in CH3NH3PbI3 (MAPbI3) solar cells, to improve the fill factor (FF) and device stability. The graded ETL was made by mixing phenyl-C61-butyric acid methyl ester (PCBM) molecules and C60-diphenylmethanofullerene-oligoether (C60-DPM-OE) molecules using the spin-coating method. The formation of the graded ETLs can be due to the phase separation between hydrophobic PCBM and hydrophilic C60-DPM-OE, which was confirmed by XPS depth-profile analysis and an electron energy-loss spectroscope. Comprehensive studies were carried out to explore the characteristics of the graded ETLs in MAPbI3 solar cells, including the surface properties, electronic energy levels, molecular packing properties and energy transfer dynamics. The elimination of the s-shape in the current density–voltage curves results in an increase in the FF, which originates from the smooth contact between the C60-DPM-OE and hydrophilic MAPbI3 and the formation of the more ordered ETL. There was an improvement in device stability mainly due to the decrease in the photothermal induced morphology change of the graded ETLs fabricated from two fullerene derivatives with distinct hydrophilicity. Consequently, such a graded ETL provides dual-functional capabilities for the realization of stable high-performance MAPbI3 solar cells.

Asymmetrical Ladder-Type Donor-Induced Polar Small Molecule Acceptor to Promote Fill Factors Approaching 77% for High-Performance Nonfullerene Polymer Solar Cells.

In this work, an effectual strategy of constructing polar small molecule acceptors (SMAs) to promote fill factor (FF) of nonfullerene polymer solar cells (PSCs) is first reported. Three asymmetrical SMAs of IDT6CN, IDT6CN-Th, and IDT6CN-M, which own large dipole moments, are designed and synthesized. The PSCs based on three polar SMAs exhibit apparently higher FFs compared with their symmetrical analogues. The asymmetrical design strategy accompanied with side chain and end group engineering makes IDT6CN-Th- and IDT6CN-M-based nonfullerene PSCs achieve high power conversion efficiency with FFs approaching 77%.