Voltage Of Solar Cells Research Articles

Organic photovoltaic electron acceptors showing aggregation-induced emission for reduced nonradiative recombination.

We introduce a facile method to generate aggregation-induced emission (AIE) properties in fused-ring electron acceptors through tetraphenylethylene decoration. Organic solar cells (OSCs) based on the AIE photovoltaic materials show decreased nonradiative energy loss during the energy conversion progress, with improvements in the open circuit voltage and device efficiency.

Performance Analysis of Different Solar Models Based on the Solar cell Parameters

In this paper author present performance analysis between solar models based on accuracy, temperature, solar irradiance, resistances, output voltage and ideality factor of solar cell. In past literature various model of solar cell are presented, like one diode model and double diode model. This paper describes a comparative analysis between one-diode, two-diode and three-diode models of PV cell. To examine the accuracy of each model from information given through the past researcher, this paper differentiates the current-voltage (I-V) and power-voltage (P-V) characteristics performance at standard test condition (STC). The utmost frequently used models are one-diode and two-diode models, as they offer healthier relationships with a real solar cell. Authors compared different solar cell models based on above parameter and found that one-diode model provides supplementary accurate result as related to two-diode model for high intensity solar irradiation. While two-diode model is further correct for short intensity solar irradiation.

Narrow band-gap materials with overlapping absorption simultaneously increase the open circuit voltage and average visible transmittance of semitransparent organic solar cells

Overlapping near-infrared absorption not only does not reduce short-circuit current density (JSC), but also can ensure a high average visible transmittance (AVT) and get a high open-circuit voltage (VOC) and power conversion efficiency (PCE) at the same time.

Fabrication of bulk heterojunction organic photovoltaic and effect of buffer layer on the basic solar cell parameters

The poly(3-hexylthiophene-2,5-diyl):phenyl C61 butyric acid methyl ester (P3HT:PCBM) organic material is important for BHJ organic solar cells. In this study PEDOT:PSS layer was coated on ITO using spin coater and thereon coated P3HT:PCBM (1:1) as fotoactive layer. Finally, Al contacts have been evaporated for electrical measurements and device structure completed. In other example, 2 nm LiF evaporated on P3HT:PCBM before metal. Electrical characterization of the devices performed with current density–voltage (J–V) measurement at room temperature and a solar simulator under an 100 mW/cm2 irradiation intensity. Basic solar cells parameters as short circuit current density (JSC), open circuit voltage (VOC), fill factor (FF) and power conversion efficiency (PCE) of the organic solar cells were determined with the measurement. Efficiency of organic solar cells increased 0.85% to 1.87% using LiF as buffer layer. Similary, LiF layer was increased other parameters of device and obtained more stabil the device.

The importance for nanostructures in N-I-P ambiguously defined Si periodic concentrated solar devices

Arrays of periodic one-dimensional nano materials provide light–matter interaction in terms of tunable optical properties which are attractive for planning efficient optoelectronic devices. This paper is based on n-i-p thin-film amorphous silicon utilizes scaffolds of vertically aligned carbon nanotube (CNT) array for a fabrication of bottom-up grown Nano pillar (NP) array solar cells. The varying effect of the CNT extent over a wide range from 800 to 2000 nm on electrical properties of the solar cells and optical were examined. The NP solar cell with CNT extent over a range of 800 nm show ‘moth-eye’ broadband antireflection effort and the value 10% lower than an average reflectance. The enhanced optical absorption relocates to significant enhancements in quantum efficiency and photocurrent contrast to a conventional planar solar cell under low light circumstances. The open-circuit voltage (Voc) of the NP solar cell was established uniformly correlated with the illumination condition and CNT spacing. The main importance is to develop high efficiency one-dimensional nanostructured solar cells results were presented here.

Sensitization of TiO2 by merocyanine dye in the presence of plasmon nanoparticles

The process of sensitization of TiO2 films by merocyanine dye in the presence of Ag/TiO2 core/shell nanoparticles (NPs) was studied. It was shown that in the presence of plasmonic Ag/TiO2 NPs an increase in the fluorescence intensity of the merocyanine dye by 30% was recorded. The fluorescence lifetime of the dye practically does not change in the presence of Ag/TiO2 NPs. It was assumed that the fluorescence enhancement of dye is associated with an increase in the excitation rate of dye molecules. The efficiency of sensitization of titanium dioxide films with a merocyanine dye increases in the presence of Ag/TiO2 NPs and accompanied by a growth in the short-circuit current density and open-circuit voltage of solar cells.

Understanding of the Nearly Linear Tunable Open-Circuit Voltages in Ternary Organic Solar Cells Based on Two Non-fullerene Acceptors.

Although the power conversion efficiencies (PCEs) of the state-of-the-art organic solar cells (OSCs) have exceeded 17%, the organic photovoltaic devices still suffer from considerable voltage losses compared with the inorganic or perovskite solar cells. Therefore, the optimization of open-circuit voltage (VOC) is of great significance for the improvement of the photovoltaic performance of OSCs. The origins of VOC have been well-established in the binary system; however, the understanding of VOC in non-fullerene acceptor (NFA)-based ternary OSCs is still lacking. Herein, we have developed a series of ternary organic photovoltaic devices, exhibiting nearly linear increased VOC as the increase of ITIC third content. We found that both the effective charge-transfer (CT) states and the nonradiative recombination losses of the bulk-heterojunction (BHJ) are altered in the ternary blends, and they collectively contribute to the tunable VOC. Our results provide a perspective for understanding the origin of VOC in NFA-based ternary OSCs.

Temperature and Light Modulated Open‐Circuit Voltage in Nonfullerene Organic Solar Cells with Different Effective Bandgaps

AbstractThe relationship of the temperature–light intensity dependence of open‐circuit voltage Voc in nonfullerene‐based organic solar cells with their material characteristics and multimechanism recombination parameters is described. The systematic variation of the effective bandgap Eg,eff and the electrode layers allows the observation of different relative contributions of bimolecular, bulk, and surface trap‐assisted recombination mechanisms. The complementary advantages of the analytical model and the established voltage‐impedance spectroscopy technique provide a useful tool to quantify multimechanism recombination parameters, effective density of states Nc, and energetic disorder σ in organic solar cells under operating conditions. The validity of the proposed model to understand the temperature and light intensity dependent of Voc is shown by applying it to four different donor:nonfullerene acceptor blend systems with conventional or inverted device architectures.

Characteristic of Methyl-Ammonium Lead Bromide Perovskites Solar Cells Fabricated By One-Step Spin Coating Process for the Application of Transparent Photovoltaics

Perovskite solar cells (PSCs) based on organic-inorganic halide have experienced an unprecedentedly rapid development when the first efficient perovskite-based solar device with solid-state structure was reported in 2009. Also, solution-processed organic-inorganic halide perovskites are currently established as the hottest area of interest in the world of photovoltaics, ensuring low manufacturing cost and relatively simple process and high conversion efficiencies. Methylammonium lead bromide (MAPbBr3) is one of the researched halide perovskite materials for transparent photovoltaics and high open circuit voltage (Voc) solar cells. Here, we have investigated MAPbBr3 absorber layer to increase the Voc and average visible transmittance. The MAPbBr3 perovskite films were fabricated by one-step spin coating process. The properties of MAPbBr3 perovskite films were found to be strongly influenced by the time to spray of anti-solvent solution (chlorobenzen). The result that the MAPbBr3 layer appropriately sprayed with chlorobenzen is beneficial to film quality and device efficiency because the nucleation of MAPbBr3 layer was affected by the anti-solvent engineering, which affected the film crystallite, density, and surface morphology. The MAPbBr3 layer by optimized 7~8 second (time to spray after spinning) showed the best efficiency of above 6.5 % with reproducibility. This research was also supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT & Future Planning (NRF-2019R1A2C4070248).

Development of High Performance C-Rich a-SiC Semiconductors with Narrow-Optical Gap By Control of Its Phase Structure

1. Introduction For the expansion of application fields (ex. tailor-made photocatalysts and high-efficiency laser) of semiconductor, novel semiconductor materials with variable optical gaps in the range from 1.2 to 3.0 eV is necessary to be developed. The promising candidate of these semiconductor is carbon-rich amorphous silicon-carbon alloy (C-rich a-SiC).[1] The optical gaps (Eog) of C-rich a-SiC can be changed from 1.2 to 2.7 eV by changing the Si/C ratio. Hetero-junction solar cell comprising N-doped C-rich a-SiC with Eog = 2.7 eV and p-type Si have been reported to show the function of photon to electron conversion.[2] However, solar cells comprising N-doped C-rich a-SiC with Eog from 1.2 to 1.7 eV showed extremely lower conversion efficiencies. Therefore, all of these C-rich a-SiC with Eog from 1.2 to 2.7 eV may not be applied to photoelectronic devices. The objective of this study is to realize C-rich a-SiC with lower Eog (frim 1.2 to 1.7 eV) that have higher semiconductor property and are able to be applied to photoelectronic devices. a-SiC has a multiphase structure in which amorphous Si-C network (Si:C = x:1-x), sp2-hybridized carbon cluster (sp 2 clusters), and silicon-like clusters (Si-cluster) coexist. It has been reported that excess sp2 cluster worked as a recombination center of photoexcited carries. It results in the degradation of efficiencies of photon to electron conversion. In order to realize C-rich a-SiC with lower Eog and higher photon to electron conversion efficiency, the synthesis method that can enhance of ratio of C/Si in amorphous Si-C network and suppress the formation of sp 2 clusters in C-rich a-SiC is necessary to be developed. In this study, CVD synthesis using high-frequency and lower power r. f. plasma was tried to be adopted to induce two types of structural change at C-rich a-SiC. High-frequency and lower power r. f. plasma can avoid the formation of sp 2 clusters in C-rich a-SiC. It results in the semiconductor materials with lower Eog and higher photon to electron conversion efficiency.2. Experimental Nitrogen-doped C-rich a-SiC thin films were synthesized by radio frequency plasma enhanced chemical vapor deposition system (RF-PeCVD) (13.56 MHz, SAMCO Co., Ltd. Model BPD-1) using tetramethylsilane, 1,1,3,3-tetrametyldisilazane and n-hexanes as source materials. C-rich a-SiC thin films were deposited on glass plate and boron-doped silicon (100) substrate (resistivity of 2 W cm) after an in-situ sputter cleaning with argon ions. Substrate temperature was kept at 160 degree C during CVD deposition. The frequency of r.f. power supply was set at 60 MHz and r.f power were changed from 5 to 26 W. The deposition time was 80 minutes. Transmission spectra of N-doped C-rich a-SiC deposited on glass substrates were examined by UV-Vis spectrophotometer (JASCO Co., Ltd. V-670). The performance of heterojunction solar cells was investigated by current-voltage (I-V) measurement (KEYSIGHT, B2901A) with simulated AM 1.5 sunlight (ASAHI SPECTRA, HAL-320). 3. Results and Discussion Eog estimated from transmission spectra (Fig. 1) of resulting N-doped C-rich a-SiC were found to be in the range from 1.40 to 2.96 eV, as shown in Table 1. Eog was able to be controlled to lower value (1.4 eV) thorough the change of the S/C ratios in C-rich a-SiC (by changing the volume ratio of n-hexane in source materials). All hetero-junction solar cells comprising N-doped C-rich a-SiC with various Eog and p-type Si crystal were confirmed to show the function of photon-to electron conversion (Table 1). The improvement of function of photon to electron conversion at C-rich a-SiC with lower Eog (ca. 1.4 eV) might be caused by the suppression of the recombination of photo-exited electrons and holes. In Figure 1, the absorption peak of sp 2 clusters was observed at 1.1 eV and was clearly separated from the absorption peak of amorphous Si-C network (observed at 2.6 eV). The intensity decrease and peak shift to lower energy side of the absorption of sp 2 clusters in Fig. 1 indicates the decrease of the amount of sp 2 clusters and the enlargement of size of sp 2 clusters. These structural change might cause the suppression of recombination of photo-carriers. The relation between Eog and open circuit voltage of solar cell was consistent with estimated value from electronic structure of C-rich a-SiC. It was summarized that the development of C-rich a-SiC semiconductors with lower Eog (in the range from 1.4 to 1.7 eV) that are able to be applied to photo-electronic devices was successfully achieved. 4.

Bis(pyrrolidino)[60]fullerenes: promising photostable fullerene-based acceptors suppressing light-induced absorber degradation pathways

Two novel highly soluble bis(pyrrolidino)[60]fullerenes were synthesized and investigated as promising electron acceptor materials for organic solar cells. Reduced electron affinity of bis(pyrrolidino)[60]fullerenes as compared to the reference [60]PCBM enabled a spectacular increase in open-circuit voltage of organic bulk heterojunction solar cells by ~200 mV while using model P3HT and PCDTBT electron donor polymers. In addition to the improved optoelectronic properties, bis(pyrrolidino)[60]fullerenes were found to be resistant towards the photochemical cross-linking in contrast to conventional [60]PCBM and conjugated polymers. Most importantly, the designed fullerene derivatives efficiently suppressed photooxidation of conjugated polymers as revealed by ESR spectroscopy, which features a tremendous potential of applying these materials in the development of efficient and durable organic photovoltaics.

Improvement of Cu2ZnSnS4 thin film performance by using oxygen-containing Cu-Zn-Sn precursor

The CZTS thin film fabricated based on Cu-Zn-Sn (CZT) or Cu-Zn-Sn-S precursors have difficulties in making a pinhole-free and flat CZTS thin film. In this paper, Cu2ZnSnS4(CZTS) thin films were fabricated based on oxygen-containing Cu-Zn-Sn precursors. By intentionally introducing O into Cu-Zn-Sn precursors, sudden volume expansion from precursor to CZTS thin films can be avoided and smooth CZTS film surfaces without pinholes were produced. Oxygen-containing Cu-Zn-Sn precursors were prepared by sputtering ZnO, Cu, and Sn targets successfully. MoS2 formation could be suppressed by introducing ZnO as a barrier layer between CZTS absorber and Mo back contact interface during the sulfurizing process under high sulphur pressure. The short circuit current density (Jsc) and open circuit voltage (Voc) of CZTS solar cells could be increased by optimizing the sulfurization temperature. And the best conversion efficiency of CZTS solar cells from oxygen-containing precursors was 4.97 %, with an open circuit voltage of 566 mV, a short circuit current density of 21.44 mA/cm-2 and a fill factor of 41 %.

Tuning the Work Function of the Metal Back Contact toward Efficient Cu2ZnSnSe4 Solar Cells

Carrier collection is crucial for thin film photoelectronic devices. As photoelectronic devices, the undesirable energy band structure between the metal contact and p‐type absorber is a serious limitation to boost the open‐circuit voltage (VOC) of thin film solar cells. Herein, the carrier collection near the back contact of a kesterite solar cell is promoted by tailoring the work function of the back contact. By diffusing P into Mo back contact of the kesterite solar cell, the work function of the Mo back contact is increased from 4.68 to 5.62 eV and the diffused P bonds with Mo as anions, thus resulting in the energy band bending upward at the back interface and enabling the fluent transmission of holes. The efficiency of Cu2ZnSnSe4 solar cells increases from 6.8% to 11.28%. The results expand the path to improving carrier collection in solar cells and electronic devices utilizing metal film contacts.

Heptacyclic S,N-Heteroacene-Based Near-Infrared Nonfullerene Acceptor Enables High-Performance Organic Solar Cells with Small Highest Occupied Molecular Orbital Offsets.

The reduction of energy offsets between donors and acceptors is a direct way to improve the open-circuit voltage (VOC) and overall performance of organic solar cells (OSCs). In this work, two nonfullerene acceptors (NFAs) (BDTBO-4F and BDTBO-4Cl) were synthesized, which were composed of a heptacyclic S,N-heteroacene core and terminal units with halogen atoms, where the latter modulates the energy level of the frontier molecular orbital. Consequently, BDTBO-4Cl exhibited a deeper highest occupied molecular orbital level (EHOMO) and lowest unoccupied molecular orbital level (ELUMO) than BDTBO-4F. Moreover, these two NFAs exhibited high electron mobility and strong absorption at 700-900 nm. The polymer donor PM6 was combined with BDTBO-4F and BDTBO-4Cl, and the resulting OSCs exhibited outstanding power conversion efficiencies of 14.83% for the PM6:BDTBO-4F device and 13.87% for the PM6:BDTBO-4Cl device. More encouragingly, these OSCs exhibited efficient hole transfer from NFAs to PM6, despite small ΔEHOMO(D-A) values (<0.10 eV). These results prove that modulation of EHOMO of acceptors to decrease ΔEHOMO(D-A) is an efficient strategy for high-performance OSCs.

Enhancing Open‐Circuit Voltage in Gradient Organic Solar Cells by Rectifying Thermalization Losses

In virtually all solar cells, including optimized ones that operate close to the Shockley–Queisser (SQ) limit, thermalization losses are a major, efficiency‐limiting factor. In typical bulk heterojunction organic solar cells, the loss of the excess energy of photocreated charge carriers in the disorder‐broadened density of states is a relatively slow process that for commonly encountered disorder values takes longer than the charge extraction time. Herein, it is demonstrated by numerical modeling that this slow relaxation can be rectified by means of a linear gradient in the donor:acceptor ratio between anode and cathode. For experimentally relevant parameters, open‐circuit voltage () enhancements up to ≈0.2 V in combination with significant enhancements in fill factor as compared to devices without gradient are found. The enhancement can be understood in terms of a simple nonequilibrium effective temperature model. Implications for existing and future organic photovoltaics (OPV) devices are discussed.

Enhancing Open-Circuit Voltage of High-Efficiency Nonfullerene Ternary Solar Cells with a Star-Shaped Acceptor.

The ternary strategy has been widely used in high-efficiency organic solar cells (OSCs). Herein, we successfully incorporated a mid-band-gap star-shaped acceptor, FBTIC, as the third component into the PM6/Y6 binary blend film, which not only achieved a panchromatic absorption but also significantly improved the open-circuit voltage (VOC) of the devices due to the high-lying lowest unoccupied molecular orbital (LUMO) of the FBTIC. Morphology characterizations show that star-shaped FBTIC molecules are amorphously distributed in the ternary system, and the finely tuned ternary film morphology facilitates the exciton dissociation and charge collection in ternary devices. As a result, the best PM6/Y6/FBTIC-based ternary OSCs achieved a power conversion efficiency (PCE) of 16.7% at a weight ratio of 1.0:1.0:0.2.

New insight on the open‐circuit voltage of perovskite solar cells: The role of defect‐density distribution and electric field in the active layer

SummaryIn this article, we study the J–V characteristic of a perovskite solar cell (PSC) prepared by the two‐step method. PSCs were fabricated by methylammonium lead iodide using the sequential deposition method. We describe J–V curves using a modified dynamic electrical model based on an asymmetric electric field. In addition, we simulated the PSCs by solar cell capacitance simulator package to investigate the role of trap‐density distribution in cell performance. The experimentally optimized device shows an enhancement in the open‐circuit voltage (VOC) from 1.08 to 1.21 V. Simulation results show that the increase in VOC up to 1.15 V is corresponding to a trap‐density of 2.38×1015 cm−3. However, these results predict that a decrease in the trap‐density can increases the VOC and FF up to 1.19 V and 79% while the modified dynamic electrical model gives the J–V characteristic as well as experimental results. Our results suggest that the increase in VOC can be attributed to the asymmetric electric field at the interface of the perovskite layer.

Impact of Local Back-Surface-Field Thickness on Open-Circuit Voltage in PERC Solar Cells: An Experimental Study Applying ANOVA to Determine Critical Sample Size Necessary to Differentiate Mean LBSF Values With Statistical Significance

Sufficiently deep local back-surface-fields (LBSF) are crucial for achieving low contact recombination and thus high solar cell efficiencies in passivated emitter and rear contact (PERC) solar cells. In this article, we investigate spatial variations of LBSF thickness 1) across dashed contacts, 2) between lateral positions within a cell, and 3) from cell to cell. The objective of this experimental study is to proof the impact of LBSF thickness on open-circuit voltage in PERC solar cells. Our measurements and analysis of variance (ANOVA) reveal that variations in LBSF thickness across dashed contacts exceed observed variations in LBSF thickness between lateral positions within a cell as well as cell-to-cell variations. Thus, we statistically treat all LBSF measurements of a single experimental group of PERC solar cells as one population of measurements. The two investigated experimental sets of PERC cells fired using different fast-firing profiles show a difference in LBSF thickness of about 1 μm. The resulting difference in open-circuit voltages arises to 1.3 mV. ANOVA-based analysis shows for our experimental samples that at least 19 random measurements are necessary in order to resolve LBSF thickness difference of 0.5 μm with sufficient statistical significance.

Structural, optical and excitonic properties of urea grading doped CH3NH3PbI3 thin films and their application in inverted-type perovskite solar cells

—The structural, optical and excitonic characteristics of urea doped CH3NH3PbI3 (MAPbI3) multi-crystalline thin films were investigated by using the X-ray diffraction patterns, atomic-force microscopic images, absorbance spectra, photoluminescence (PL) spectra and Raman scattering spectra. The surface-sensitive Raman scattering spectra show that the urea small molecules are mainly distributed in the top region of the MAPbI3 thin films and thereby effectively passivating the electron-poor defects (interfacial MA cations) of MAPbI3 thin films. Besides, the thermal annealing temperature and the concentration of urea additive both strongly influence the formation of MAPbI3 thin films, which dominates the photovoltaic performance. The use of 5-wt% urea can increase the open-circuit voltage (VOC) and short-circuit current density (JSC) of the MAPbI3 solar cells from 0.88 V to 19.75 mA/cm2 to 0.94 V and 22.97 mA/cm2, respectively. In addition, the reduced current hysteresis in the J-V curves of the MAPbI3 solar cells can be explained as due to the effective defect passivation in the top region of the MAPbI3 thin film by the oxygen-donors of the urea small molecules.

Simulation of plano-convex cylindrical lens effects on photovoltaic solar cells efficiency

A method for control and modification of solar cell efficiency using a plano-convex cylindrical lens is proposed. Optical effects of a plano-convex cylindrical lens placed on a solar cell are detailed theoretically and numerical simulations are used to modify the efficiency of the cell. It was found that the lens could reduce the incident angle of the beam and enhance the solar cell voltage. The output power from the solar cell could be controlled using this lens during the day and a modification method is proposed in order to gain more output power from a solar cell. This method is a low cost and green method to gain controllable output voltage from the photovoltaic solar cells. Experiments confirm the effectiveness of this method.