Voltage Of Solar Cells Research Articles

Semi-transparent p-type barium copper sulfide as a back contact interface layer for cadmium telluride solar cells

Optically transparent p-type materials play a critical role in transparent electronics including photovoltaic (PV) devices. P-type sulfide materials offer an alternative to oxides for PV application due to improved hole transport properties. Here, we report the solution-based synthesis of earth-abundant p-type transparent conducting barium copper sulfide (α-BaCu4S3, BCS) thin films. These films were characterized using scanning electron microscopy, X-ray diffraction, UV–Vis–NIR spectrophotometry, Raman spectroscopy, and spectroscopic ellipsometry. BCS films of ~100 nm thickness transmit >70% of visible light. We report on tests of the hole transport properties of these BCS films for cadmium telluride (CdTe) photovoltaics, finding that the BCS deposition process forms a beneficial tellurium (Te) rich surface on CdTe by selectively removing Cd from the surface. Based on our study, the BCS interface layer plays dual functions for CdTe PV devices as a hole transport material and as an etchant, enhancing the resulting device performance. We observed a significant increase in open-circuit voltage of CdTe solar cells with the BCS buffer layer. Additionally, we discuss semitransparent CdTe solar cells with BCS as a hole transport layer and indium tin oxide as a finishing electrode. Semitransparent CdTe solar cells shows 13.3% conversion efficiency for the front side illumination and 1.2% efficiency for back side illumination, indicating high recombination of charge carriers generated close to the rear CdTe/BCS/ITO contact.

Tailoring methyl-ammonium lead bromide nanostructure by solvent engineering and their application to high open circuit voltage solar cells

Methyl-ammonium lead bromide (MAPbBr3) perovskite films were fabricated by two-step deposition process. We used two common organic solvents, N, N-Dimethylformamide and Dimethyl sulfoxide (DMSO), which is commonly used to fabricate lead halide films. In this work, we used these solvents in both steps of the spin coating process to fabricate nanostructured MAPbBr3 perovskite films. When DMF was employed; a uniform, dense, compact sub-micron size perovskite nanocube arrays perovskite film was observed. However, when DMSO was employed; nanorod and microplate perovskite films were observed. In contrast to conventional two-step spinning processing, this process has better well organized and submicron size nanocrystals. The best performing device employing MAPbBr3 micro/nano-cubes active layer (using DMF) has a power conversion efficiency of (PCE) of 5.88% and the best performing device employing MAPbBr3 nanorods/microplates active layer (using DMSO) has a PCE of 4.22%. This finding will help the researcher to fabricate well-organized nanocube/nanorods/microplate-array based perovskite solar cells.

Open-circuit voltage of organic solar cells: Effect of energetically and spatially nonuniform distribution of molecular energy levels in the photoactive layer

Abstract Here, the open-circuit voltage (VOC) of organic solar cells (OSCs) in which the energy levels of the frontier molecular orbitals of the photoactive materials vary depending on the position within the active layer is investigated. The VOC in these devices is critically affected by the energy level of the frontier molecular orbitals that are spatially located near the electrodes (i.e., the highest occupied molecular orbital of the donor near the anode and the lowest unoccupied molecular orbital of the acceptor near the cathode). Other parameters such as the charge generation/recombination and the energy distribution of charge-transfer states appear to exert less influence on the VOC. This work demonstrates that, to maximize the VOC, the spatial distribution of molecular energy levels should be controlled, especially in OSCs that exhibit spatial variation of the energy levels of organic materials within their active layer.

Novel small oligothiophene molecules with phenylene and naphthalene cores as promising absorber materials for organic solar cells

New small molecules bearing either phenylene or naphthalene core in combination with thiophene and rhodanine periphery moieties were synthesized by the Stille cross-coupling reaction. Their evaluation for prototypes of organic solar cells showed that replacing phenylene moiety by the naphthalene one caused decrease in the HOMO energy, while the open-circuit voltage and fill factors of solar cells based on these materials were significantly improved to manifest maximum power conversion efficiencies to 5.3%.

Low-Cost High-Sensitive Suns–$V_{\text{oc}}$ Measurement Instrument to Characterize c-Si Solar Cells

Measuring open-circuit voltage (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">oc</sub> ) versus light intensity (Suns) in solar cells permits the access of cell performance without the series resistance effect. This article shows the implementation of a Suns-Voc measurement system that consists of an off-the-shelf photograph flash lamp, a digital oscilloscope, and a specifically designed photodetector board with three silicon photodiodes that covers a light intensity measurement range from 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> to 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> suns. The whole system is controlled via universal serial bus (USB) ports from a personal computer allowing the measurement of cell characteristics (pseudo-dark and pseudo-light current density-voltage curves, as well as the pseudo fill factor and pseudo efficiency) automatically in a very short time.

Enhanced efficiency and reduced hysteresis by TiO2 modification in high-performance perovskite solar cells

Recent research has focused on increasing the open-circuit voltage (VOC) and current density (JSC) of perovskite solar cells (PSCs) by introducing p- or n-type dopants with higher electronegativity than Ti into the TiO2 electron transport layer (ETL). However, these kinds of dopant create undesired charge traps that hinder charge transport through TiO2. Therefore, the improvement in VOC is often accompanied by an undesired current density–voltage (J–V) hysteresis problem. Herein, we demonstrate that the introduction of 4-chlorobenzoic acid (4-ClBA-TiO2) dopant into TiO2 not only overcomes the J–V hysteresis issue but also increases the VOC, JSC and power conversion efficiency (PCE) in mesoscopic PSCs. Also, the material shown the better device performance compared to the state-of-art ETL, with the 4-CLBA-TiO2. We speculate that the interaction between the 4-ClBA and the perovskite interface is more selective for electrons. Further the 4-ClBA-TiO2 electron mobility has been improved 1.9 times compared with TiO2. As a result, for mesoscopic PSCs, the doping of 4-ClBA-TiO2 increases the efficiency from 18.23% to 20.22%, while the hysteresis is largely reduced from 20.2% to 1.5%. To the best of our knowledge, this is the first report using the spin coating blocking layer to achieve over 20%. Thus, we believe that this approach will be an effective design strategy capable of enhancing the performance of PSCs with less hysteresis.

On the recombination order of surface recombination under open circuit conditions

Understanding the recombination dynamics of organic and perovskite solar cells has been a crucial prerequisite in the steadily increasing performance of these promising new types of photovoltaics. Surface recombination in particular has turned out to be one of the last remaining roadblocks, which specifically reduces the open circuit voltage. In this study, the relationship between the rate of surface recombination and the density of charge carriers is analyzed, revealing a cubic dependence between these two parameters. This hypothesis is then tested and verified with the recombination dynamics of an organic solar cell known to exhibit significant surface recombination and a high energy proton irradiated CH 3 NH 3 PbI 3 perovskite solar cell during white light illumination. Incidentally, these results can also explain recombination orders exceeding the commonly known threshold for bimolecular recombination that have been observed in some studies without the need for a charge carrier dependent bimolecular recombination coefficient. • Surface recombination specifically reduces the open circuit voltage in organic and perovskite solar cells. • A cubic relationship between the rate of surface recombination and the charge carrier density has been derived. • This hypothesis has been successfully tested for organic and perovskite solar cells. • Recombination orders β > 2 can now be explained without charge carrier density dependent k bm .

Reduced bilateral recombination by functional molecular interface engineering for efficient inverted perovskite solar cells

Interface-mediated recombination losses between perovskite and charge transport layers are one of the main reasons that limit the device performance, in particular for the open-circuit voltage (VOC) of perovskite solar cells (PSCs). Here, functional molecular interface engineering (FMIE) is employed to retard the interfacial recombination losses. The FMIE is a facile solution-processed means that introducing functional molecules, the fluorene-based conjugated polyelectrolyte (CPE) and organic halide salt (OHS) on both contacts of the perovskite absorber layer. Through the FMIE, the champion PSCs with an inverted planar heterojunction structure show a remarkable high VOC of 1.18 V whilst maintaining a fill factor (FF) of 0.83, both of which result in improved power conversion efficiencies (PCEs) of 21.33% (with stabilized PCEs of 21.01%). In addition to achieving one of the highest PCEs in the inverted PSCs, the results also highlight the synergistic effect of these two molecules in improving device performance. Therefore, the study provides a straightforward avenue to fabricate highly efficient inverted PSCs.

Reducing energy loss via tuning energy levels of polymer acceptors for efficient all-polymer solar cells

The open-circuit voltage (Voc) of all-polymer solar cells (all-PSCs) is typically lower than 0.9 V even for the most efficient ones. Large energy loss is the main reason for limiting Voc and efficiency of all-PSCs. Herein, through materials design using electron deficient building blocks based on bithiophene imides, the lowest unoccupied molecular orbital (LUMO) energy levels of polymer acceptors can be effectively tuned, which resulted in a reduced energy loss induced by charge generation and recombination loss due to the suppressed charge-transfer (CT) state absorption. Despite a negligible driving force, all-PSC based on the polymer donor and acceptor combination with well-aligned energy levels exhibited efficient charge transfer and achieved an external quantum efficiency over 10% while maintaining a large Voc of 1.02 V, leading to a 9.21% efficiency. Through various spectroscopy approaches, this work sheds light on the mechanism of energy loss in all-PSCs, which paves an avenue to achieving efficient all-PSCs with large Voc and drives the further development of all-PSCs.

TiO2-based dye-sensitized solar cells prepared with bixin and norbixin natural dyes: Effect of 2,2’-bipyridine additive on the current and voltage

In this paper, we discovered that the 2,2′-bipyridine (bipy) was able to increase the voltage and short circuit current of dye-sensitized solar cells (DSSCs) prepared using bixin and norbixin natural dyes that are environmentally friendly. Titanium oxide (TiO2) film was deposited on FTO-glass. Morphological analysis revealed that the film was porous and consisted of almost spherical particle with an average size of 35 nm. The photoelectric behavior of the DSSCs was evaluated under polychromatic radiation adjusted to 1.5 AM standard. The analysis revealed that the presence of bipy in the electrolyte significantly increased the open circuit voltage (VOC) values from 299 to 519 mV for the DSSCs prepared using bixin dye, whereas the VOC values increased from 293 to 311 mV for the DSSCs prepared using norbixin dye. Also, it was observed that the bipy additive positively influenced the short-circuit current (JSC) values of these devices. The simultaneous increase in VOC and JSC rendered this bipyridinic compound a good additive candidate for TiO2 nanoparticles-based DSSC using natural dyes.

Defect properties of solar cells with layers of GaP based dilute nitrides grown by molecular beam epitaxy

Dilute nitrides lattice-matched to GaP were studied to explore the possibilities to improve their properties by additional indium or arsenic content in the GaPN alloy for further utilization in solar cells. Admittance spectroscopy shows that intrinsic layers of GaPNAs and InP/GaPN grown by molecular-beam epitaxy have unintentional background silicon donor doping. Deep-level transient spectroscopy allowed us to reveal several defect levels. In GaPNAs, two defect levels were detected at Ec − 0.58 eV and Ev + 0.44 eV, with respective concentrations of 4 × 1015 cm−3 and 2 × 1015 cm−3. After thermal annealing, these could be reduced by a factor of two and by more than one order of magnitude, respectively, leading to an increase of external quantum efficiency and open-circuit voltage of solar cells. The InP/GaPN layer exhibits a defect level at Ec − 0.44 eV (with a concentration of 2 × 1014 cm−3), which is of similar nature as the one at Ec − 0.58 eV in GaPNAs. Furthermore, unlike in GaPNAs, defect levels close to midgap were also detected in the InP/GaPN layer. These non-radiative recombination centers lead to poorer photoelectric properties of solar cells based on InP/GaPN as compared to those based on GaPNAs. Therefore, the introduction of arsenic in the compound and post-growth thermal annealing allowed us to reduce the defect concentrations in dilute nitrides and improve photoelectrical properties for photovoltaic applications.

High-performance piezo-phototronic multijunction solar cells based on single-type two-dimensional materials

Abstract Piezotronics and piezo-phototronics based on the third-generation semiconductor (such as ZnO, GaN, CdS, and monolayer chalcogenides) and two-dimensional materials, have attracted increasing attention due to the coupling characteristic of piezoelectric, photon excitation, and semiconductor properties. Strain can not only induce piezoelectric charges but also modulate bandgap of piezotronic materials. In this paper, we propose a structure of piezo-phototronic multijunction solar cell based on single-type two-dimensional piezoelectric semiconductor materials. By using the theory of detailed balance limit, the open circuit voltage and short circuit current of this piezo-phototronic multijunction solar cell are calculated. The results indicate that power conversion efficiency of the piezo-phototronic multijunction solar cell can theoretically reach to 33%, under the blackbody of temperature 6000 K, which is higher than the well-known theoretical Shockley-Queisser limit. This work provides guidance to design the next generation ultra-high performance piezo-phototronic solar cells.

Hybrid Quantum Dot/Organic Heterojunction: A Route to Improve Open-Circuit Voltage in PbS Colloidal Quantum Dot Solar Cells

We have successfully demonstrated the effect of a thin organic bulk-heterojunction (BHJ) interlayer on improving the photovoltaic performance of lead sulfide (PbS) colloidal quantum dot (CQD) solar...

Experimental investigation of thin-film solar cells as a wearable power source

ABSTRACT In this paper, a design for a wearable solar energy harvesting system with an embroidered electrical circuit is proposed. The hybrid simulation method is carried out by using MATLAB/Simulink and LTSpice simulation software’s to extract the unknown electrical parameters of the multi-junction solar cell. A DC-DC boost converter (LTC3105) with MPPC is experimented to step up the solar cell voltage to 5 V. The solar energy harvester model achieves optimum simulated results in the LTSpice software with MPPT for both sunny and artificial shading conditions. The maximum conversion efficiency of the solar energy harvesting system with MPPC is 73.46 with an output voltage of 5 V and 68.29 at 4.10 V output voltage for flat and bent conditions, respectively. The fabricated system is tested in various conditions such as flat, bent condition with radius of 5.5 cm and artificial shading. The fabricated flexible solar cell power source can easily supply the power to wearable electronic, wireless sensors, and biomedical sensors. The solar cell and boost converter are integrated with jeans textiles to make whole system as wearable one and electrical connections are embroidered with conductive yarn. The fabricated wearable solar cell power source can easily supply the power to wearable biomedical sensors.

Dominant recombination mechanism in perovskite solar cells: A theoretical study

Different recombination losses have been shown to play a role in the photocurrent and photovoltage loss of lead halide perovskite solar cells. While it is believed that trap density is extremely small in high-efficiency perovskite cells, trap-assisted recombination cannot be ruled out due to the existence of tail states, for instance at the grain boundaries. In this study, the optical and electrical performance of a perovskite solar cell of the structure: ITO/PEDOT:PSS/CH3NH3PbI3/PC61BM/LiF/Al was modelled using numerical drift-diffusion simulations with embedded optical modelling via the transfer matrix method. The total recombination was calculated as the sum of bimolecular recombination and recombination via tail states. The influence of charge carrier mobility on photovoltaic parameters (short-circuit current, fill factor, open-circuit voltage, and power conversion efficiency) of perovskite solar cells was studied. Next, the impact of Urbach energy on the recombination process was investigated by simulation of bimolecular and tail state recombination rates as a function of voltage for various values of Urbach energy. It was shown that by increasing the Urbach energy, the bimolecular recombination rate decreases, but the tail state recombination rate increases at all voltages. Furthermore, the slope of the open-circuit voltage-light intensity curve, the light ideality factor, demonstrates the dominant recombination at different Urbach energy levels. It was found that the slope increases from 1.04 at EU = 25 meV to1.65 at EU = 150 meV. It can be concluded that the bimolecular recombination is the dominant recombination at low EU, while the tail state recombination overcomes the bimolecular recombination at high EU.

Improving the voltage of GaAs solar cells with In0.4Ga0.6As nanostructures

The fundamental reason for the decrease in solar cell (SC) voltage when introducing nanostructures has been found. It consists in the fact that recombination redistributes between nanostructures and bulk GaAs. It has been shown that, by changing the position of the nanostructure medium in p–i–n GaAs SCs, it is possible to partially suppress recombination and improve voltage while maintaining the increase in short-circuit current. The decrease of recombination via nanostructures provides an increase in SC efficiency from 19.87% to 21.94%.

Titanium Dioxide (TiO&lt;sub&gt;2&lt;/sub&gt;) Doped Reduced Graphene Oxide (rGO) with Different Dye for Solar Cell Application

In the present work, the surface morphology and electrical characteristic of different doping ratio of reduced Graphene Oxide (rGO) in Titanium Oxide solution with different organic dyes (turmeric and beetroot) were studied. The Titanium Dioxide (TiO2) solution and reduced Graphene Oxides (rGO) were synthesized by using precipitation-peptization method and chemical reagent, respectively. The TiO2-rGO thin film was deposited on the glass substrate by using doctor-blade technique. The surface morphology and electrical characteristic were measured by using Scanning Electron Microscope (SEM) and Keitheley 2450 Source Meter, respectively. Experimental results showed that 0.3 wt% rGO with turmeric dye resulted the highest value of open voltage (Voc) and short circuit current (Isc) of Dye-sensitized Solar Cells (DSSC).

Synthesis, Optical and Electrochemical Properties of Two Series Electron-Donor Polymers with Diphenylpyranylidene Side Chain

Two series of novel conjugated polymers with diphenylpyranylidene as the side chain and thiophene as the main chain were designed, synthesized and characterized as electron donors of polymer solar cells for the first time. The absorption spectra showed that introduction of diphenylpyranylidene side chain can obviously complement the light absorption ability in the range from 300-500 nm. In addition, diphenylpyranylidene unit is also helpful to tune the HOMO energy level as low as -5.23 to -5.31 eV than P3HT polymers, for favoring higher open-circuit voltage in polymer solar cells.

High Open-circuit Voltage and Low Voltage Loss in All-polymer Solar Cell with a Poly(coronenediimide-vinylene) Acceptor

Reducing the voltage loss (Vloss) is a critical factor in optimizing the open-circuit voltage (Voc) and overall power-conversion efficiency (PCE) of polymer solar cells. In the current work, by designing a novel electron-accepting unit of coronenediimide (CDI) and using it as the main functional building block, a new polymer acceptor CDI-V is developed and applied to fabricate all-polymer solar cells. Compared with the perylenediimide-based polymer acceptors we previously reported, the current CDI-V polymer possesses a noticeably elevated lowest unoccupied molecular orbital (LUMO). Thereby, by virtue of the enlarged energy gap between the donor HOMO and acceptor LUMO, a high Voc value of 1.05 V is achieved by the all-polymer photovolatic device, along with an impressively low Vloss of 0.55 V. As remarkably, in spite of an extremely small LUMO level offset of 0.01 eV exhibited by the donor and acceptor polymers, effective charge separation still takes place in the all-polymer device, as evidenced by a proper short-circuit current (Jsc) of 9.5 mA·cm2 and a decent PCE of 4.63%.

Reduction of interface recombination current for higher performance of p+-CZTSxSe(1-x)/p-CZTS/n-CdS thin-film solar cells using Kesterite intermediate layers

There have been significant efforts to enhance the performance of CZTS thin-film solar cells. However, the increase in series resistance, formation of the unfavorable MoS2 between the absorber layer and back-contact, and recombination losses are some of the most effective factors for the low values of the efficiency and open-circuit voltage parameters. In this paper, five experimental CZTS solar cells with high efficiency of 8.4–11% have been mainly studied and discussed. Afterwards, two experimental works have been reproduced to validate our results. Additionally, with introducing the thin CZTSxSe(1-x) layer between the Mo back-contact and CZTS absorber layer, the efficiency and open-circuit voltage of solar cells have been notably improved. There is a significant decrease in recombination losses (less than 12 mA/cm2) after using CZTSxSe(1-x) intermediate layers between the absorber layer and back-contact. Using the CZTSe, and CZTS0.2Se0.8 thin layers and optimizing the structure as p+pn structure (p+-CZTSxSe(1-x)/p-CZTS/n-CdS), the following efficiencies (and open-circuit voltage) are achieved as: 15.98% (921 mV) and 17.81% (986 mV), respectively. Simulations demonstrate that at 0.8-V bias for p+-CZTS0.2Se0.8/p-CZTS/n-CdS structure, the recombination current total density is reduced to 6.47 mA/cm2. To obtain the highest performance in the proposed structures, the absorber layer carrier concentration should be 1 × 1016 cm−3 and the intermediate layer carrier concentration needs to be within the range of 1 × 1017 cm−3 to 1 × 1018 cm−3. Furthermore, the optimum thickness of CZTSe and CZTSSe intermediate layers in the proposed structures is 50 nm.