Open-circuit Voltage Of Solar Cells Research Articles

Efficiency and stability enhancement in FA-based perovskite solar cells using controlled reduction of graphene oxide interlayer – An experimental investigation

Reduced graphene oxide (rGO) as an interlayer and interface engineer, due to its conductivity and hydrophobicity, can be coated on top of perovskite layers to increase the photovoltaic performance and stability of perovskite solar cells. Herein, we employed reduced graphene oxide as an interlayer. By controlling the reduction level of rGO, its potential for boosting perovskite solar cells' efficiency was further increased. Results showed that increasing the reduction degree of rGO to an optimal level increased its conductivity and hole mobility, which induced charge transfer at perovskite/hole transport layer and increased the open-circuit voltage of solar cells. Our rGO reduction controlling strategy enables FAPbI3-based solar cells to record a PCE of 22.29%. In addition, increasing reduction degree increased hydrophobicity behavior of rGO. It increased perovskite solar cell resistance against humidity and heating degradation. The developed method in current study can push up perovskite solar cells to industrialization.

Surface Photovoltage Method for Photovoltaic Quality Control of GaAs-Based Solar Cells

In this paper, we demonstrate the potential of the contactless surface photovoltage (SPV) method for fast and reliable control of GaAs-based solar cells directly on epitaxial heterostructures before metallization and photolithography processes. The magnitude of the SPV corresponds to the generated photovoltage in the photoactive region, which is related to the open circuit voltage of the cell. The focus of this investigation is the potential of dilute nitride compounds grown by low-temperature liquid-phase epitaxy (LPE) for application as intermediate cells in multijunction solar cells. First, SPV spectroscopy is used to determine the photosensitivity spectral range and bandgap of the grown dilute nitride compound layers. Further, the photovoltaic quality of the grown solar cell heterostructures is evaluated by comparing the magnitude of their SPV signals with that of a reference GaAs solar cell. A drastic reduction in the measured SPV is observed for nitrogen-containing solar cell structures, which correlates with the lowering of solar cell open-circuit voltage values measured under standard test conditions. Finally, solar cell structures based on nitrogen-free GaAsSb compounds with the same long-wavelength photosensitivity limit as GaAsSbN are grown by LPE. They show one order of magnitude higher SPV signal and, therefore, have a great potential for solar cell application.

Intrinsic Photoconductivity Spectral Dependence as a Tool for Prediction of Open-Circuit Voltage in Organic Solar Cells

Organic materials are known for their variety of molecules. Methods to predict the parameters of organic photovoltaic (OPV) cells are required to avoid the time- and resource-consuming processes of manufacturing and testing OPVs. Usually, the open-circuit voltage (Uoc) is estimated as the difference between the ionization energy level of the electron donor molecule (Id) and the electron affinity level of the electron acceptor molecule (EAa). Various measurement methods are used to determine the energy level values of pure materials, which, when combined with energy level shifts due to the donor:acceptor interactions, make these estimations less precise. In this work, photoconductivity measurements were applied to the donor:acceptor films. Near threshold energy, the electron can be directly transferred from the donor to the acceptor molecule. The obtained charge transfer energy (ECT) shows the difference between Id and EAa in the film. This difference was compared to the Uoc value of an OPV made of the same donor:acceptor combination. We show that this approach provides less scattered results and a higher correlation coefficient compared to the Uoc estimation using energy level values.

Temperature dependent behavior of sub-monolayer quantum dot based solar cell

This work investigates the temperature dependence of the performance of In(Ga)As-based solar cells made from sub-monolayer (SML) quantum dots (QDs), quantum wells (QWs), and Stranski-Krastanov QDs (SK-QDs). Well-defined sub-bandgap peaks are observed in external quantum efficiency (EQE) spectra for all samples. Apparently, changes in minority carrier lifetime affect both the sub-bandgap and the above bandgap EQE. Lateral confinement of carriers in the SMLs and QDs also affects the temperature dependence of the EQE. Finally, a “U” shaped curve was observed from the temperature dependence of the short-circuit current (ISC) from these nanostructure-based solar cells. This is due to the competition between the decreasing bandgap and the increasing carrier loss to recombination within the nanostructures as the temperature increases. In contrast, the solar cell's open-circuit voltage and power efficiency decrease monotonically with temperature.

Creating metal saturated growth in MOCVD for CdTe solar cells

Determining the thermodynamic conditions in MOCVD growth of II-VI semiconductor materials is not as straightforward as in III-V growth where Group V hydrides are generally used. This paper establishes a technique, using in situ laser reflectometry, to ensure that the thermodynamic equilibrium is under metal saturated growth. This has been applied to the arsenic doping of CdTe solar cells where it was shown that increasing the II/VI precursor ratio resulted in an increase in As dopant incorporation. The growth kinetics were determined by the diisopropyl tellurium (DIPTe) concentration for II/VI precursor ratios above 2. A method is presented where the change in II/VI precursor ratio can be predicted for different positions in a horizontal MOCVD chamber that has, in turn, enabled variation in NA and the solar cell open circuit voltage (Voc) to be determined as a function of the II/VI precursor ratio. This gives new insight to the thermodynamic drivers in MOCVD growth for improved solar cell Voc and is a method that could be applied to MOCVD of other II-VI semiconductors.

Improved performance of TiO2 nanoarray/BiOI heterojunction all-solid-state solar cells by incorporating BiFeO3 perovskite interlayer

The photovoltaic conversion of heterojunction solar cells relies on the interface properties between n-type and p-type semiconductors. N-type TiO2-nanoarray (NA), ferroelectric BiFeO3 interlayer, and p-type BiOI were used to fabricate a ternary bulk heterojunction using a solution-based method in this study. Solid-state solar cells of FTO/TiO2-NA/BiFeO3/BiOI/spiro-OMeTAD/Ag are constructed for the first time, and their photo-electric conversion performance is studied. The addition of a BiFeO3 interlayer at the interface between TiO2-NA and BiOI increased the solar cell open-circuit voltage (Voc) from 0.18 to 0.47 V and the short-circuit current (Jsc) from 0.29 to 0.54 μA/cm2, resulting in a nearly 5-fold increase in power conversion efficiency. The Kelvin Probe force microscope analysis confirmed that the polarization electric-field (Eself) generated by the BiFeO3 interlayer is directed toward BiOI, thereby increasing the surface potential and decreasing electron and hole back flows between TiO2 and BiOI. This additional electric field caused greater charge concentrations and a greater Voc. Furthermore, the Eself directed toward the BiOI increased the built-in electric field (Ebi) in the space charge area from TiO2 to BiOI, allowing for greater separation of photogenerated electrons and holes and thus raising the Jsc. The findings of this study suggested that manipulating internal electric fields via polarization could be an effective method for enhancing the performance of solar cells based on BiOI.

Effect and optimization of the Zn3P2 back surface field on the efficiency of CZTS/CZTSSe tandem solar cell: a computational approach

Copper zinc tin sulfide (CZTS) and copper zinc tin sulfo selenide (CZTSSe) kesterite minerals are nontoxic and abundant in the earth with the promise of cost-effective photovoltaic applications. This study explains a tandem solar cell made of kesterite materials that can capture sunlight over a broad spectrum. The proposed tandem structure comprises a wide bandgap CZTS thin-film upper subcell and an underlying narrow bandgap CZTSSe-based lower subcell. The upper and lower subcells are simulated using solar cell capacitance simulator-one dimension and validated against the experimental results to determine the viability of the proposed tandem design. Additionally, the performance of both subcells is evaluated for tandem configuration by adding a back surface field layer, a modification of the back contact, testing at different thicknesses, and doping of both subcell absorber layers. As a result, optimizing both subcells improved tandem solar cell open-circuit voltage (V oc) to a maximum of 1.5 V, which led to an efficiency of 23.99% at the current matching condition. Furthermore, how light radiation power and temperature variations impact the proposed solar cell performance is being investigated. This study provides significant insights into efficient tandem solar cell design and manufacture.

D-A-D Structured Polymer Interlayer for Higher Open-Circuit Voltage and Stability in MAPbI3 Perovskite Solar Cells

D-A-D Structured Polymer Interlayer for Higher Open-Circuit Voltage and Stability in MAPbI3 Perovskite Solar Cells

Optical simulation and design of high-absorption thin-film perovskite halide solar cells based on embedded quadrilateral cluster nanoparticles

Recently, thin-film organic–inorganic hybrid perovskite solar cells have a high efficiency-to-cost ratio. However, due to the thickness of the absorber layer, photon management in the absorber layer is still not optimized. This research suggests an embedded side for the plasmonic perovskite solar cells. Using Maxwell equations solver (finite-difference time-domain method), numerical optimization of photocurrent for gold, copper, silver, and aluminum cluster of nanoparticles in different geometries including quadrilateral, hexagonal, octagonal, and dodecagonal was investigated at a wavelength range from 300 nm to 800 nm. Moreover, the basic factors of optical simulation such as absorption coefficient, generation rate, and electric field distribution are shown in the optimal case, and the important parasitic absorption challenge for the cluster of nanoparticles was considered in the calculation of the net absorption. The reference cell uses a perovskite absorber (CH3NH3PbI3) with a thickness of 250 nm, which can significantly reduce the amount of lead, and the solar cell's toxicity. The photocurrent density for the optimized case utilizing spherical cluster of nanoparticles is obtained 21.74mAcm−2, which is enhanced by approximately 25.6% compared to perovskite solar cells without nanoparticles. Finally, the best-case cluster nanoparticle is coated with an ultra-thin-film SiO2 layer, to help the chemical and thermal stability of metallic nanoparticles in the photoactive region. According to the final proposed model, the photocurrent of 22.28mAcm−2 and enhancement of 28.72% were obtained. Besides, the proposed solar cell's open-circuit voltage, fill factor, and conversion efficiency are calculated at around 1.003 V, 0.88, and 19.71%, respectively.

3‐D Modeling of Ultrathin Solar Cells with Nanostructured Dielectric Passivation: Case Study of Chalcogenide Solar Cells (Adv. Theory Simul. 11/2021)

3-D Modeling of Ultrathin Solar Cells In article number 2100191, Waseem Raja, Erkan Aydin, Thomas G. Allen, and Stefaan De Wolf develop a novel 3-D optoelectrical finite-element model to analyze the performance of ultrathin solar cells. In particular, the 3-D model investigates the light trapping and field passivation in which the negative charges induced on the nanostructured passivation layer repel the minority charge carriers, increasing the solar cell's open-circuit voltage and power conversion efficiency.

Slow Relaxation of Photogenerated Charge Carriers Boosts Open-Circuit Voltage of Organic Solar Cells.

Among the parameters determining the efficiency of an organic solar cell, the open-circuit voltage (VOC) is the one with most room for improvement. Existing models for the description of VOC assume that photogenerated charge carriers are thermalized. Here, we demonstrate that quasi-equilibrium concepts cannot fully describe VOC of disordered organic devices. For two representative donor:acceptor blends, it is shown that VOC is actually 0.1–0.2 V higher than it would be if the system was in thermodynamic equilibrium. Extensive numerical modeling reveals that the excess energy is mainly due to incomplete relaxation in the disorder-broadened density of states. These findings indicate that organic solar cells work as nonequilibrium devices, in which part of the photon excess energy is harvested in the form of an enhanced VOC.

Numerical Simulation Analysis of Ag Crystallite Effects on Interface of Front Metal and Silicon in the PERC Solar Cell

In the fabrication of crystalline silicon solar cells, the contact properties between the front metal electrode and silicon are one of the most important parameters for achieving high-efficiency, as it is an integral element in the formation of solar cell electrodes. This entails an increase in the surface recombination velocity and a drop in the open-circuit voltage of the solar cell; hence, controlling the recombination velocity at the metal-silicon interface becomes a critical factor in the process. In this study, the distribution of Ag crystallites formed on the silicon-metal interface, the surface recombination velocity in the silicon-metal interface and the resulting changes in the performance of the Passivated Emitter and Rear Contact (PERC) solar cells were analyzed by controlling the firing temperature. The Ag crystallite distribution gradually increased corresponding to a firing temperature increase from 850 ∘C to 950 ∘C. The surface recombination velocity at the silicon-metal interface increased from 353 to 599 cm/s and the open-circuit voltage of the PERC solar cell decreased from 659.7 to 647 mV. Technology Computer-Aided Design (TCAD) simulation was used for detailed analysis on the effect of the surface recombination velocity at the silicon-metal interface on the PERC solar cell performance. Simulations showed that the increase in the distribution of Ag crystallites and surface recombination velocity at the silicon-metal interface played an important role in the decrease of open-circuit voltage of the PERC solar cell at temperatures of 850–900 ∘C, whereas the damage caused by the emitter over fire was determined as the main cause of the voltage drop at 950 ∘C. These results are expected to serve as a steppingstone for further research on improvement in the silicon-metal interface properties of silicon-based solar cells and investigation on high-efficiency solar cells.

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.

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.

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.

Fabrication and comparison of Heterojunction solar cells from CdS/PbS nanoparticles and CdS/PbS bulk

PbS nanoparticles and CdS nanoparticles are grown by chemical methods. Also bulk PbS is grown by simple chemical methods without using any capping agent. The material formation is identified from XRD.TEM image shows the formation of different shaped PbS nanoparticles, CdS nanoparticles, and bulk PbS. Three different heterojunction solar cells are fabricated by CdS and PbS samples using a spin coating technique. Finally, gold is evaporated on PbS film. Current-voltage characteristics data for three heterojunction solar cells are taken under dark and illumination conditions. For each fabricated solar cell open-circuit voltage (VOC), short circuit current density (ISC), fill factor (FF), and power conversion efficiency() are measured. Finally, a comparison of the characteristics is done for different fabricated heterojunction solar cells.

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.

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...

25.11% efficiency silicon heterojunction solar cell with low deposition rate intrinsic amorphous silicon buffer layers

Here we report a certified efficiency of up to 25.11% for silicon heterojunction (SHJ) solar cells on a full size n-type M2 monocrystalline-silicon (c-Si) wafer (total area, 244.5 cm2). An ultra-thin intrinsic a-Si:H buffer layer was introduced on the c-Si wafer surface using a 13.56 MHz home-made RF-PECVD with low deposition rate showing superior surface passivation. The ultra-thin i-a-Si:H film with both higher microstructure factor (R*) and H content evidently increases the SHJ solar cell open-circuit voltage (VOC) by 2 mV, and moreover, short-circuit current (ISC) and fill factor (FF) are also notably improved, resulting in a 0.52% absolute cell efficiency enhancement, in which FF is the main cause. In order to explore high conversion efficiency SHJ solar cells, both home-made RF-PECVD and commercial VHF-PECVD (40.68 MHz) are employed for deposition of the i-a-Si:H passivation layer. As a result, the efficiency of RF-PECVD-prepared SHJ cell is 0.21% higher than that of VHF-PECVD-prepared, mainly driven by VOC and ISC boost. This work offers a useful tool for fabrication of high performance SHJ solar cells which could be employed in mass production.