Decrease In Short-circuit Current Density Research Articles

Red-color-modulated perovskite solar cells with copper(I) thiocyanate/cellulose acetate–based distributed Bragg reflectors

Abstract This study investigates the development of perovskite solar cells (PSCs) equipped with distributed Bragg reflectors (DBRs) through a coating-based fabrication technique. The incorporation of DBRs enhanced the esthetic appeal and improved the light absorption properties of PSCs, rendering them suitable for building-integrated photovoltaics (BIPV). The DBRs, composed of 3–11 layers of copper(I) thiocyanate and cellulose acetate, exhibited peak reflectance at 700 nm. However, as the number of DBR layers increased, there was a corresponding decrease in short-circuit current density (Jsc) and power conversion efficiency (PCE) due to greater light reflection. Specifically, compared with PSCs without DBRs, those with 11-layer DBRs showed 41.2% and 39.0% reduction in Jsc and PCE, respectively. Despite these reductions, this study highlights the potential of colored PSCs for practical BIPV applications, achieving a balance between esthetics and efficiency.

First-principles calculation analysis and photovoltaic properties of Cu compound-added perovskite solar cells

Experiments and first-principles calculations were performed to investigate the effects of Cu substitution in CH3NH3PbI3 perovskite crystals. The first-principles calculations indicated that the energy level of the Cu d orbital formed above the VB maximum would be an acceptor or defect level. The effect of Cu addition on device properties was investigated, and the device with added 2% Cu provided higher efficiencies than the standard device. On the other hand, the decrease in short-circuit current density with increasing Cu content would be attributed to the defect level of the Cu d orbitals. First-principles calculations and experimental results provided insight into the function of Cu in CH3NH3-based perovskite crystals.

Effect of temperature and pre-annealing on the potential-induced degradation of silicon heterojunction photovoltaic modules

We investigate the effect of temperature and pre-annealing on the potential-induced degradation (PID) of silicon heterojunction (SHJ) photovoltaic (PV) modules. SHJ PV modules show a faster decrease in short-circuit current density (J sc) at higher temperatures during PID tests. We also observe a complex relationship between the degree of the J sc decrease and temperature during the PID tests. Pre-annealing before the PID tests at sufficiently high temperatures leads to the complete suppression of the PID of SHJ PV modules. The decrease in J sc is known to be due to the chemical reduction of indium (In) in transparent conductive oxide (TCO) films in SHJ cells, in which water (H2O) in SHJ modules is involved. These indicate that H2O may out-diffuse from the SHJ PV modules during a PID test or pre-annealing at sufficiently high temperatures, by which the chemical reduction of indium in TCO to metallic In is suppressed.

Improving the efficiency of industrial samples of silicon solar elements

Possibilities of increasing the efficiency by more than 20 % for silicon photoelectric converters made in China have been investigated. It has been established by the method of computer simulation that the life-times of nonequilibrium charge carriers, which are 520 μs, realized in such photoelectric converters, do not limit the possibility of increasing their efficiency by more than 20 %. It is shown that an increase in the photocurrent density to 43.1 mA/cm2 leads to an increase in efficiency to 20.1 %, and a decrease in the diode saturation current density to 3.1∙10-14 A/cm2 leads to an increase in efficiency to 20.4 %. Simultaneous change of these diode characteristics leads to an increase in efficiency to 23.1 %. The paper proposes physical and technological approaches to increase the photocurrent density and reduce the diode saturation current density in ready-made photovoltaic converters. The study of the influence of operating temperature on the efficiency of crystalline silicon photoelectric converters is carried out in the article. It is shown that with increasing operating temperature the relative decrease in the efficiency of single-crystal devices is –0.7 relative %/C, which is significantly higher than in the instrument structures of European production and due to non-traditional decrease in short-circuit current density. Mathematical modeling of the influence of light-emitting diode characteristics on the efficiency of crystalline silicon solar cells showed that the decrease in the efficiency of instrument structures with increasing operating temperature is due not only to an increase in diode saturation current density from 10-13 A to 3·10-13 A, which is 300 %, but also by reducing the shunt resistance from 2.5 kOhm to 1.5 kOhm. A study of the effect of operating temperature on the diode saturation current showed that the height of the potential barrier in the studied silicon photovoltaic converters is 0.87 eV, due to the insufficient level of doping of the base material. The limited height of the potential barrier leads to an unconventional decrease in the shunt resistance with increasing operating temperature.

Effects of Intrinsic Layer Thickness on the Short-Circuit Current Density of Crystalline Silicon-Based Solar Cells

The amount of short-circuits current density (Jsc) shown in the results of the electrical characterization of silicon (c:Si)-based solar cell diodes is one of the determinants of device performance. Efforts to increase Jsc are carried out by adding pure silicon to the diode junction, thereby increasing the magnitude of photoelectron generation in the material. In this paper, the insertion of an intrinsic semiconductor at various thicknesses will be analyzed for its effect on the characteristics of the resulting current-voltage density. By using a 2D simulation based on the finite element method, the solution to the equation of a solar cell semiconductor with a p-i-n junction structure becomes the basis for calculating the resulting electric current density. The thickness variation of the simulated layer i ranges from 1 μm to 15 μm, with a constant thickness of p and n layers of 0.4 m. The simulation results show that the reduced thickness of the intrinsic layer has a significant effect on the decrease in short-circuit current density.

Modeling Thermo-Mechanical Stress of Flexible CIGS Solar Cells

Copper indium gallium diselenide (CIGS) thin-film solar cells are fabricated through several deposition and annealing processes at high temperatures, which can generate significant thermal residual stress to solar cells. Moreover, since CIGS solar cells with flexible substrates are rollable and bendable, they are susceptible to mechanical stresses during these processes. In addition, partial shading (hotspot) can exert high heat on the CIGS solar cell. In this paper, we investigate the thermo-mechanical stress of each active layer of CIGS solar cells due to annealing, external bending, and hotspot using finite element method (FEM). We found that average stress of each active layer decreases and maximum stress in the cell increases when interface crack is introduced between cadmium sulfide (CdS)/CIGS. Our overarching goal is to quantify the relationship between the fabrication/operating process and the reliability of CIGS solar cells (energy release rate and internal stresses), which could improve the reliability of flexible solar cells. It is also found that lowering the annealing temperature can reduce the stresses in the cells and lowering CIGS thickness can reduce the delamination probability of CdS/CIGS interface. Finally, we investigate the effect of the crack length of the CdS/CIGS interface on the electrical performance of CIGS solar cells through FEM simulations. We found that as the crack size between CdS and CIGS layers increases, short-circuit current density decreases, while open-circuit voltage remains almost constant.

Impact of copper on light-induced degradation in Czochralski silicon PERC solar cells

Both multicrystalline and Czochralski (Cz) silicon substrates are known to suffer from various mechanisms of light-induced degradation (LID), including copper-related LID (Cu-LID). Past studies on Cu-LID have mostly been performed on unprocessed wafers, omitting the impact of the solar cell process on the copper distribution. Here, we carefully contaminate Cz-substrates of different quality with different amounts of copper and process the substrates into complete industrial Cz-Si PERC solar cells, reaching a comprehensive mapping of the impact of Cu-LID for the PV industry. The results show that both the copper contamination level and Cz crystal quality are critical factors affecting the extent of Cu-LID. Most importantly, we show that copper can result in significant concentrations in the bulk of the finished PERC cells after being exposed to only trace surface contamination. Consequently, even a small local copper contamination area (~ 3–4 cm2) is sufficient to induce strong LID in the full-sized (156 × 156 mm2) cell parameters, resulting e.g. in ~7% relative efficiency loss during light soaking. The corresponding short circuit current density decreases by up to a factor of two in the contaminated areas.

Fabrication of Core-Shell Structured TiO<sub>2</sub>/MgO Electrodes for Dye-Sensitized Solar Cells

We demonstrated the construction and performance of dye-sensitized solar cells (DSCs) based on nanoparticles of TiO2 coated with thin shells of MgO by simple solution growth technique. The XRD patterns confirm the presence of both TiO2 and MgO in the core-shell structure. The effect of varied shell thickness on the photovoltaic performance of the core-shell structured electrode is also investigated. We found that MgO shells of all thicknesses perform as barriers that improve open-circuit voltage (Voc) of the DSCs only at the expense of a larger decrease in short-circuit current density (Jsc). The energy conversion efficiency was greatly dependent on the thickness of MgO on TiO2 film, and the highest efficiency of 4.1% was achieved at the optimum MgO shell layer.

Effects of hydrogen plasma treatment on SnO2:F substrates for amorphous Si thin film solar cells

We investigated the effects of hydrogen plasma treatment on the physical and electrical properties of fluorine-doped tin oxide (FTO) films used for amorphous silicon (a-Si) thin film solar cells. A slight increase in carrier concentration by the hydrogen doping effect was observed for the FTO film exposed to the hydrogen plasma for 5 min. For further exposure to the plasma, the chemical reduction became prominent and resulted in deterioration of the electrical and optical properties of the film. XPS analysis revealed that the chemical reduction of SnO2 to Sn metallic state occurs on the surface region. It was found that the defects formed by hydrogen plasma act as recombination centers at the interface between FTO electrode and p-layer of a-Si solar cells. This phenomenon resulted in the deterioration of the cell performance. The averaged conversion efficiency (6.82%) of the cells on pristine FTO hydrogen substrate was decreased to 5.81% for the cells on FTO treated for 5 min, which is mainly attributed to the decrease in short-circuit current density.

Substrate versus superstrate configuration for stable thin film silicon solar cells

We report on the light-induced degradation kinetics of hydrogenated polymorphous silicon (pm-Si:H) solar cells having either substrate or superstrate device configuration. Both types of devices were exposed to light-soaking for 500h. While pm-Si:H superstrate solar cells showed strong degradation (up to 60%) under mercury vapor lamp illumination, we have found that substrate structures are remarkably stable. The difference between the two types of devices is shown to be related to interface delamination which only occurs in superstrate devices. We further demonstrate a strong correlation between short-circuit current density decrease upon light-soaking and solar cell area loss.

Effects of Hole-Collecting Buffer Layers and Electrodes on the Performance of Flexible Plastic Organic Photovoltaics

Here we report the influences of the sheet resistance (Rsheet) of a hole-collecting electrode (indium tin oxide, ITO) and the conductivity of a hole-collecting buffer layer (poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate), PEDOT:PSS) on the device performance of flexible plastic organic photovoltaic (OPV) devices. The series resistance (RS) of OPV devices steeply increases with increasingRsheetof the ITO electrode, which leads to a significant decrease of short-circuit current density (JSC) and fill factor (FF) and power conversion efficiency, while the open-circuit voltage (VOC) was almost constant. By applying high-conductivity PEDOT:PSS, the efficiency of OPV devices with highRsheetvalues of 160 Ω/□ and 510 Ω/□ is greatly improved, by a factor of 3.5 and 6.5, respectively. These results indicate that the conductivities of ITO and PEDOT:PSS will become more important to consider for manufacturing large-area flexible plastic OPV modules.

ChemInform Abstract: Development of Fullerene Derivatives with High LUMO Level Through Changes in π‐Conjugated System Shape

AbstractReview: 15 refs.

Tio2 Paste Formulation for Crack-Free Mesoporous Nanocrystalline Film of Dye-Sensitized Solar Cells

Using a doctor-blade method, a highly viscous titanium dioxide (TiO2) paste was deposited on a glass substrate coated with fluorine doped tin oxide (FTO). The paste was mainly composed of commercially available TiO2 nanoparticles (P25) and hydroxypropyl cellulose (HPC) as organic filler. Varying the content of HPC in the TiO2 paste changed the physical properties of the mesoporous TiO2 layer, particularly its porosity and surface area. From the quantification of dyes on Ti2, layer and the electrochemical impedance spectroscopy (EIS) study of the dye-sensitized solar cells (DSSCs), the surface area of the TiO2 film was found to have decreased. This came with the increase of HPC content while the porosity of the film increased, consistent with the concurrent decrease of short-circuit current density (Jsc) and efficiency (eta). The increased porosity greatly affected the electron transport through the TiO2 film by decreasing the coordination number of the TiO2 particles resulting to a decrease of the electron diffusion coefficient.

Using high haze (> 90%) light-trapping film to enhance the efficiency of a-Si:H solar cells

The high haze light-trapping (LT) film offers enhanced scattering of light and is applied to a-Si:H solar cells. UV glue was spin coated on glass, and then the LT pattern was imprinted. Finally, a UV lamp was used to cure the UV glue on the glass. The LT film effectively increased the Haze ratio of glass and decreased the reflectance of a-Si:H solar cells. Therefore, the photon path length was increased to obtain maximum absorption by the absorber layer. High Haze LT film is able to enhance short circuit current density and efficiency of the device, as partial composite film generates broader scattering light, thereby causing shorter wave length light to be absorbed by the P layer so that the short circuit current density decreases. In case of lab-made a-Si:H thin film solar cells with v-shaped LT films, superior optoelectronic performances have been found (Voc=0.74V, Jsc=15.62mA/cm2, F.F.=70%, and η=8.09%). We observed ~35% enhancement of the short-circuit current density and ~31% enhancement of the conversion efficiency.

Development of fullerene derivatives with high LUMO level through changes in π-conjugated system shape

This article describes a concept for designing fullerene-based electron-accepting materials to obtain high open-circuit voltage (V OC) in organic thin-film photovoltaic devices without an accompanying decrease in short-circuit current density. The keys to this concept are (1) reducing the size of the fullerene π-conjugated system to realize high V OC and (2) shortening the inter-fullerene distance in the solid-state packing structure to achieve high short-circuit current density (J SC), which is made possible by well-designed supramolecular organization or a small organic addend. In this article, two representative examples are discussed. One is 1,4-bis(silylmethyl)[60]fullerene (SIMEF), which forms a columnar fullerene-core array for high electron mobility and undergoes thermal crystallization for good phase separation with the electron-donating material. The other is a 56π-electron fullerene derivative bearing a dihydromethano group, the smallest carbon addend, which does not disrupt fullerene–fullerene contact in the solid state.

Fullerene acceptor for improving open-circuit voltage in inverted organic photovoltaic devices without accompanying decrease in short-circuit current density

A poly(3-hexylthiophene) (P3HT)-based inverted organic photovoltaic (OPV) device with a fullerene electron acceptor, (dimethyl(o-anisyl)silylmethyl)(dimethylphenylsilylmethyl)[60]fullerene (SIMEF2), exhibited 2.9% power conversion efficiency (PCE; JSC = 7.9 mA/cm2, VOC = 0.66 V, and FF = 0.56) in the device configuration, indium tin oxide/ZnO/P3HT:SIMEF2/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)/Au under AM1.5 G illumination at 100 mW/cm2. Through a comparison with a [6,6]-phenyl-C61-butyric acid methyl ester-based device (PCE = 2.4%, JSC = 7.8 mA/cm2, VOC = 0.56 V, and FF = 0.55), SIMEF2 was found to give higher VOC without a decrease in JSC. This result marks progress toward overcoming the trade-off relationship between VOC and JSC in the development of highly efficient OPV devices.

缓冲夹层影响异质结有机光伏器件性能研究

The CuPc/buffer interlayer/C60heterojunction organic photovoltaic devices are fabricated by inserting a MoO3or RB interlayer and investigated the impact of buffer interlayer on the performance of heterojunction organic photovoltaic devices.The results suggest that OPV with the buffer interlayer has higher open-circuit voltage and power conversion efficiency,lower short-circuit current density and fill factor.The open-circuit voltage increases from 0.39Vto 0.58Vand 0.55V,respectively,and the power conversion efficiency reaches 0.44%,in comparison with a power conversion efficiency of 0.36%for OPV without interlayer.The short-circuit current density decreases from 1.92mA/cm2 to 1.77mA/cm2 and 1.81mA/cm2,and from 0.48to 0.43and 0.44in fill factor,respectively.Further research shows that the short-circuit current density strongly depends on the thickness of buffer layer.The short-circuit current density increases when the interlayer thickness is small,while it gradually decreases as the buffer layer thickness increasing.When the interlayer thickness is 10nm,the short-circuit current density decreases to 0.35mA/cm2.The open-circuit voltage enhances as the buffer layer thickness increasing,from 0.43V with 1nm interlayer to 0.63V10nm interlayer.Open-circuit voltage enhancement and the short-circuit current density decrease are studied according to the integer charge transfer model and interfacial energy level theory,which provide a research foundation for the performance improvement of organic solar cells.

Simulation of Symmetrically Doped Silicon Nanowire Solar Cells

ABSTRACTSilicon nanowire solar cells were simulated using the Silvaco TCAD software kit. For optimization of speed the simulations were performed in cylinder coordinates with cylindrical symmetry. Symmetric doping was assumed with a dopant density of 1018 cm-3 in the p-type core and inside the n-type shell. In the implementation a cathode contact was wrapped around the semiconductor nanorod and an anode was assumed at the bottom of the rod. Optimization of cell efficiency was performed with regard to the rod radius and the rod length. In both optimization processes clear maxima in efficiency were visible, resulting in an optimal radius of 66 nm with the pn junction at 43.5 nm and an optimal rod length of about 48 μm. The maximum of efficiency with respect to the rod radius is due to a decrease of short-circuit current density (Jsc) and an increase of open-circuit voltage (Uoc) with radius, while the maximum with respect to the rod length is explained by the combination of an increase of Jsc and a decrease of Uoc. Fill factors stay rather constant at values between 0.6 and 0.8. Further, the influence of a back surface field (BSF) layer was surveyed in simulations. Positioning the BSF next to the cathode contact considerably improved cell efficiency. In addition, simulations with a cathode contact on top of the nanowire structure were undertaken. No severe deterioration of cell performance with increasing radius was observed so far in this configuration. Hence, nanorods with much larger radii can be used for solar cells using this contact scheme. In comparison to simulations with wrapped cathode contacts, Jsc and Uoc and therefore efficiency is considerably improved.

ZnO−Al2O3 and ZnO−TiO2 Core−Shell Nanowire Dye-Sensitized Solar Cells

We describe the construction and performance of dye-sensitized solar cells (DSCs) based on arrays of ZnO nanowires coated with thin shells of amorphous Al(2)O(3) or anatase TiO(2) by atomic layer deposition. We find that alumina shells of all thicknesses act as insulating barriers that improve cell open-circuit voltage (V(OC)) only at the expense of a larger decrease in short-circuit current density (J(SC)). However, titania shells 10-25 nm in thickness cause a dramatic increase in V(OC) and fill factor with little current falloff, resulting in a substantial improvement in overall conversion efficiency, up to 2.25% under 100 mW cm(-2) AM 1.5 simulated sunlight. The superior performance of the ZnO-TiO(2) core-shell nanowire cells is a result of a radial surface field within each nanowire that decreases the rate of recombination in these devices. In a related set of experiments, we have found that TiO(2) blocking layers deposited underneath the nanowire films yield cells with reduced efficiency, in contrast to the beneficial use of blocking layers in some TiO(2) nanoparticle cells. Raising the efficiency of our nanowire DSCs above 2.5% depends on achieving higher dye loadings through an increase in nanowire array surface area.

Electrochemical properties of dye-sensitized solar cells fabricated with PVDF-type polymeric solid electrolytes

We have already proposed a poly(vinylidenefluoride-co-hexafluoropropylene) (PVDF-HFP)-based polymeric solid electrolyte (PSE) film for dye-sensitized solar cells (DSSCs). The employment of the PSE film, however, almost always accompanies with decrease in short-circuit current density ( J sc). We then studied electrochemical properties on the PSE-based and liquid electrolyte-based DSSCs to clarify the reason why the conversion efficiency is lower in the former than in the latter. The diffusion coefficient of I 3 − and the cell gap of DSSCs were found out to play a key role to increase J sc. In particular, the stronger cell-gap dependence was observed in the PSE-based DSSC than in the liquid electrolyte-based DSSC. This indicates that the design of DSSC structure is quite important to achieve the higher conversion efficiency in the PSE-based DSSC. We confirmed that the J sc of a PSE-based DSSC with a 20 μm cell gap is turned out to be about 97% of the J sc of a liquid electrolyte-based DSSC.