Circuit Voltage Of Solar Cells Research Articles

A theoretical investigation into the impact of temperature and band gap variation of La2NiMnO6 oxide double perovskite nanostructures on the performance of La2NiMnO6/MASnI3 based hybrid solar cells

The study aimed at simulating a model of bilayer La2NiMnO6/MASnI3 hybrid perovskite solar cell having a potential benefit of better stability at higher operating temperature with higher band gap of LNMO. This numerical analysis of La2NiMnO6/MASnI3 based hybrid solar cell performance parameters has been carried out as a function of temperature and optical band gap (Eg) of La2NiMnO6 (LNMO). The analysis reveals that the fill factor of solar cells operated at room temperature has not been affected too much on varying Eg of LNMO and decreases non-linearly with increasing operating temperature. The open circuit voltage of solar cells operated at room temperature increases with increasing Eg of LNMO and drops linearly with increasing operating temperature. The short-circuit current density (JSC) increases non-linearly at different rates with increasing the operating temperature. The value of dη/dT increases up to a critical temperature (Tc) and then decreases in the solar cells comprised with higher Eg of LNMO (Eg ∼ 1.50 eV–1.60 eV). The Tc value was shifted towards higher operating temperature in the higher Eg of LNMO (Eg ≥ 1.50 eV), enabling more stable solar cell at higher operating temperature.

High open-circuit voltage in lead sulfide quantum dot solar cells via solution-phase ligand exchange with low electron affinity cadmium halides

A solution-phase ligand exchange strategy is developed for cadmium halide ligands to passivate PbS quantum dots. The cadmium halide passivation curtails bandtail and trap states to achieve a record 0.7 V open circuit voltage in solar cells.

Enhanced Performance of Ternary CuGaSe2 Thin‐Film Photovoltaic Solar Cells and Photoelectrochemical Water Splitting Hydrogen Evolution with Modified p–n Heterointerfaces

AbstractRenewable energy sources, in particular, photovoltaic solar cells and hydrogen fuel, are expected to be the pillars of a sustainable society. Chalcopyrite CuGaSe2 (CGSe) has potential for using in such applications. This article presents efficient solar cells suitable as top cells for tandem devices and highly active photocathodes for solar hydrogen evolution using CGSe photoabsorber layers with modified p–n heterointerfaces. Rb‐doping during the last stage of CGSe film growth effectively improves the photovoltaic performance, and solar cell efficiency of >10% with a high fill factor (FF) of 74.6% is obtained. The half‐cell solar‐to‐hydrogen conversion efficiency reaches 8% with the use of a photocathode composed of a CGSe film grown in an identical growth batch. Interface modification with i) a Cu‐deficient layer, ii) alkali‐metal doping, and iii) an n‐type buffer layer formed on the CGSe film surface is found to a be key to control the energy conversion device parameters, such as the FF and open circuit voltage of solar cells and the onset potential of photoelectrochemical cells, due to the suppression of interface recombination.

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.

Correction to “Reciprocity and Open Circuit Voltage in Solar Cells” [Jan 18 67-69

Correction to “Reciprocity and Open Circuit Voltage in Solar Cells” [Jan 18 67-69

Determination of the electronic properties of Cu2ZnSnSe4-based solar cells by impedance spectroscopy and current–voltage characteristics analysis

Cu2ZnSnSe4 (CZTSe) thin films were synthesized by a cosputtering–annealing process and characterized as absorber layer of solar cells. Electrical characteristics of the solar cells were analyzed by coupling current–voltage measurements with impedance spectroscopy. The slightly p-type nature of the CZTSe absorber is evidenced with a doping level as low as 1.4 × 1015 cm−3. The solar cells exhibit a dominant recombination pathway in the space charge region in which it was revealed an apparent increase of the doping due to the ionization of deep level in the bandgap. Moreover, open circuit voltage of solar cells is found to be mainly limited by the low built-in voltage at the CdS/CZTSe interface. We conclude that the device architecture can play a major role in the electrical properties of solar cells.

High-efficiency thin film ZnMgO/ZnO solar cell simulation approach: Temperature dependency, BSF and efficient small signal analysis

Small signal analysis for Al/ZnO/c-Si/Ag heterojunction solar cell structure is investigated in this simulation work. Effect of signal frequency, device temperature and junction interface defect state density on the junction diffusion capacitance and device conductance are thoroughly examined. Built in potential measurement highlights variation from 0.8 to 2.1 eV for the range100 Hz to 8 MHz which showing a good agreement with the practical value. Low temperature (10–100 K) conductance measurement at 2 V biasing results a localised Fermi level state density 9.54 × 1040 cm−3eV−1and evidences variable range hopping conduction. Excellent improvement of short circuit current density and efficiency is observed using MgxZn1-xO window layer. The increase in short circuit current density and efficiency due to the use of the window layer are 31.85 mA cm−2 and 19.17% respectively. For all the study illumination of 400 nm monochromatic light with photon flux 2.8 × 1017 cm−2s−1 and spectral width 10 nm are applied. Uses of 400 nm light is due to study of temperature dependency on open circuit voltage of solar cell. Using 1000 wt/m2 the efficiency of solar cell is enhanced from 19.88% to 23.15%.

Improvement in open circuit voltage of solar cells with zinc sulfate-modified photoelectrodes

ABSTRACTWe report on the effects of surface-modified TiO2 on the open-circuit voltage (Voc) of dye-sensitized solar cells (DSSCs). The TiO2 films were immersed into an aqueous zinc sulfate (ZS) solution to give ZS-modified photoelectrodes. The DSSCs with ZS-modified photoelectrodes showed a considerable improvement in Voc, compared to that of the control device with pristine TiO2 layer. By monitoring open-circuit voltage decay, electrochemical impedance and dark current, it was revealed that the modification of the TiO2 surface by ZS led to a longer electron lifetime due to a reduction of interfacial charge recombination between photo-injected electrons and I−3 ions, and thereby inducing the increase in Voc.

Charge blocking layers in thin-film/amorphous photovoltaics

The open circuit voltage of solar cells is a critical property which, in many thin film devices, is found to be much lower than the theoretical limit associated with the material's absorption energy gap. A known method for improving the open circuit voltage is that of adding charge blocking layers (a.k.a. charge selective or charge transport layers). However, such interfacial layers are often found to decrease the fill factor or even cause undesired S-shape in J-V curves. In the current work, we revisit the blocking-layer method through detailed device simulations, explain how such layers enable significant Voc increase (even above the built-in voltage), and show that the layers' resistance is responsible for the problematic behavior observed. Having identified the source of reduced fill factor, we suggest methods of reducing the resistivity and recovering the fill factor.

Origin of Open Circuit Voltage in Solar Cells Based on Polymer Wrapped Carbon Nanotubes and Fullerenes

Thin films of semiconducting p-type single-walled carbon nanotubes (SWCNTs) have been recently used both for photo-absorption and for hole transport in the quest for all-carbon solar cells [1-6]. Quantum efficiency as high as 43% at the peak absorption wavelength of the nanotubes has been reported using single-chirality tubes [3]. These devices were of bilayer type, with efficiencies around 1%. More recently, bulk heterojunction (BHJ) type solar cells were also reported with a certified efficiency of 3.1% [2]. With the major focus on the interface between SWCNTs and fullerenes where the excitons generated by photo-absorption get dissociated, varying values of open circuit voltage (Voc ) have been obtained. Common to all these devices is the use of semiconducting polymers such as polyfluorene and polythiophene along with the nanotubes. During the separation process for single chirality tubes, the excess polymer is usually removed to obtain a polymer-nanotube mass ratio of 1:1. However, along with the SWCNT interfaces, there will still exist polymer-fullerene and polymer-electrode interfaces, which can influence the device performance. For example, S. Na et al [7] have shown that a polyfluorene derivative interfacial layer on the cathode side can in a BHJ solar cell with poly(3-hexylthiophene) (P3HT) and 1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C61(PCBM) can increase its efficiency. We report the effect of polymers on the performance of two single chirality SWCNT-C60 bilayer solar cells using: (a) poly(9,9-dioctylfluorene-2,7-diyl) (PFO) separated (7,5) tubes and (b) 9,9-di-octylfluorenyl-2,7-diyl and bipyridine copolymer (PFO-BPy) separated (6,5) tubes. We show that along with polymer-SWCNT weight ratio, the absolute weight of the polymer is also a critical parameter affecting the device operation. Performance of devices with and without SWCNTs both having the same polymer content is compared. In devices without SWCNTs, the polymer alone acts as interfacial layer between C60 and the anode. Polymer concentration dependence is also studied in these devices. It is found that the polymer layer, even at very low concentrations, increases the device efficiency by nearly an order of magnitude. While the reference cell with only C60 gave an efficiency of 0.07%, the devices with PFO interfacial layer had efficiencies up to 0.6% with an increase in all three efficiency determining parameters. The Voc of devices with PFO increased in the range of 0.2 -0.5 V over that of the C60 reference device, increasing with PFO layer thickness. In addition, while the PFO-SWCNT-C60 device gave a Voc of 0.40 V, PFO-C60 device gave a Voc of 0.56 V even though both devices contain equal concentration of PFO. These results indicate that the origin of Voc may be the PFO-C60 interface and that the presence of SWCNTs has a negative effect on achievable Voc . With PFO-SWCNT-C60 device working like a ternary system with PFO concentration dependent efficiency, optimization of this system should take into account the PFO-C60 interface as well.

Reversible photo-induced trap formation in mixed-halide hybrid perovskites for photovoltaics.

We report on reversible, light-induced transformations in (CH3NH3)Pb(Br x I1-x )3. Photoluminescence (PL) spectra of these perovskites develop a new, red-shifted peak at 1.68 eV that grows in intensity under constant, 1-sun illumination in less than a minute. This is accompanied by an increase in sub-bandgap absorption at ∼1.7 eV, indicating the formation of luminescent trap states. Light soaking causes a splitting of X-ray diffraction (XRD) peaks, suggesting segregation into two crystalline phases. Surprisingly, these photo-induced changes are fully reversible; the XRD patterns and the PL and absorption spectra revert to their initial states after the materials are left for a few minutes in the dark. We speculate that photoexcitation may cause halide segregation into iodide-rich minority and bromide-enriched majority domains, the former acting as a recombination center trap. This instability may limit achievable voltages from some mixed-halide perovskite solar cells and could have implications for the photostability of halide perovskites used in optoelectronics.

Influence of Cl and H2O in spray-ILGAR® solutions on the voltage gain of Cu(In,Ga)(S,Se)2 solar cells with In2S3 buffer

In2S3 thin layers can be prepared by Spray-ILGAR® (Ion Layer Gas Reaction) from indium trichloride or from indium triacetylacetonate solutions. In the first case, the film contains a controllable amount of Cl. The concentration of H2O or Cl was varied systematically in the precursor solutions that were used for the deposition of In2S3 buffer layers on commercially available Cu(Ga,In)(S,Se)2 absorbers. The layers were characterized by ultraviolet photo electron spectroscopy, optical spectroscopy, modulated surface photovoltage spectroscopy and X-ray photoelectron spectroscopy, combined with a sequential etching procedure. The latter allowed to estimate an element-specific depth profile. Experimental findings were correlated with the performance of the corresponding solar cells. The presence of H2O or Cl in the precursor solutions has a strong influence on the diffusion of Cu+ and Na+ cations from the absorber into the buffer layer. The open circuit voltage of solar cells with In2S3 buffer layers prepared from Cl-free, H2O-containing precursor solutions was higher by up to 100mV than those from Cl-containing, but H2O-free solutions. For this reason, the average solar energy conversion efficiency of cells of the first buffer type was higher (14.7%) than for solar cells of the second type (12.1%).

High open circuit voltages of solar cells based on quantum dot and dye hybrid-sensitization

A type of solar cell based on quantum dot (QD) and dye hybrid-sensitized mesoporous TiO2 film electrode was designed and reported. The electrode was consisted of a TiO2 nanoparticle (NP) thin film layer sensitized with CdS quantum dot (QD) and an amorphous TiO2 coated TiO2 NP thin film layer that sensitized with C106 dye. The amorphous TiO2 layer was obtained by TiCl4 post-treatment to improve the properties of solar cells. Research showed that the solar cells fabricated with as-prepared hybrid-sensitized electrode exhibited excellent photovoltaic performances and a fairly high open circuit voltage of 796 mV was achieved.

Closed-form model for the open circuit voltage of solar cells with shunt resistance, bias-dependent photocurrent and double exponential terms

The parasitic shunt resistance, bias dependence of the photocurrent and phenomena causing a second exponential term in the current density ( J )-voltage ( V ) equation reduce the open circuit voltage, V oc , of illuminated solar cells below the ideal value predicted by the J - V equation having only a single exponential term. This study reports an approximate closed-from solution of the transcendental V oc equation which directly reflects these losses. The solution estimates V oc as a weighted parallel combination of the limiting V oc values corresponding to the domination of one of the several terms of the V oc equation. The solution allows quick design calculation of the V oc of a wide variety of cells in terms of all physical parameters, and provides insight into the influence of losses owing to various factors.

PS27 多結晶シリコン太陽電池の発電効率に及ぼすひずみの影響

The purpose of this study is to bring out strain effects on outputs of polycrystalline silicon solar cells. Strains on crystalline silicon change the bandgap which relates to the open circuit voltage of solar cells. Strains are added by putting a load on a specimen. Strains are evaluated by the stress analysis using Finite Element Analysis and the measurement using strain gauges. The specimen was designed which can deliver 0.21 % tensile and compressive strain on the solar cells. In order to deliver strains on a base plate to solar cells, A7075-T651 was chosen as the base plate material. The base plate and solar cell modules were bonded by an epoxy adhesive. 1-V characteristics of the specimen were measured by exposing incandescent light to the specimen and the maximum output of the specimen was calculated. The maximum output of the specimen decreases 21 % with 0.126 % tensile strain.

A furan-bridged D-π-A copolymer with deep HOMO level: synthesis and application in polymer solar cells

A novel D-π-A copolymer, PFBT-BDT, based on furan-containing benzothiadiazole (FBT) and benzodithiophene (BDT) was designed and synthesized by Pd-catalyzed Stille-coupling method. The copolymer showed good solubility and film-forming ability combining with good thermal stability. PFBT-BDT exhibited a broad absorption from 300 to 630 nm with an absorption peak centered at 522 nm. The optical band gap (Egopt) determined from the onset of absorption of the polymer film was 1.96 eV. The LUMO and HOMO energy levels of the polymer were estimated to be −3.48 eV and −5.44 eV, respectively. The polymer solar cell fabricated from the blend of the polymer as donor and PC71BM as acceptor exhibited a moderate power conversion efficiency of 2.81% with a high Voc of 0.94 V without annealing and any additives. To the best of our knowledge, this is among the highest Voc values for PSCs based on benzodithiophene derivatives. This work demonstrates that the replacement of thiophene moieties in conjugated polymers with more electron-withdrawing furan moieties is able to significantly lower the HOMO energy levels, and therefore, increase the open circuit voltage of solar cells.

Nb2O5 Photoelectrodes for Dye-Sensitized Solar Cells: Choice of the Polymorph

Nanowires of Nb2O5 were developed in three polymorphic forms, namely, pseudo-hexagonal, orthorhombic, and monoclinic, by electrospinning a polymeric solution and by subsequent annealing. The materials were characterized by X-ray and electron diffraction, scanning and transmission electron microscopy, BET surface area measurements, absorption spectrometry, and cyclic voltammometry. These characterizations indicate that the monoclinic phase has a higher conduction band edge compared with the other two and is likely to display higher open circuit voltage in solar cells. Dye-sensitized solar cells were fabricated using the above polymorphs, and the device performances were studied. The pseudo-hexagonal phase showed higher device performance owing to its higher specific surface area compared with the others. However, when normalized, the device performances with respect to the dye-loading, the monoclinic phase gave superior performance. Studies on the charge transport properties using electrochemical impedance spectroscopy and open circuit voltage decay indicate that the monoclinic phase has high resistance against charge recombination and improved electron lifetime compared with the other phases and conventional TiO2 nanostructures. The monoclinic Nb2O5 is likely to be a material of choice as photoelectrode in dye-sensitized solar cells if its mesoporous particles with large surface area could be synthesized.

Study on the flatband potential of nanoporous TiO2 film electrode

The flatband potential of nanoporous TiO2 film electrodes has been studied by spectroelectrochemical method. The effect of film thickness and TiCl4 treatment on the flatband potential of nanoporous TiO2 electrodes and the photovoltaic performance of dye-sensitized solar cells were determined. The results showed that with the increasing of film thickness， the flatband potential shifts in the positive direction， and the open circuit voltage of corresponding solar cells decreases. In addition， after TiCl4 treatment， the flatband potential and the open circuit voltage of corresponding solar cells were not obviously changed. All this suggests that the flatband potential of nanoporous TiO2 electrode can reflect the changing trend of open circuit voltage of solar cells well.

Light absorption and emission in semiconductors with band gap fluctuations—A study on Cu(In,Ga)Se2 thin films

This work investigates the influence of lateral fluctuations of the fundamental band gap on the macroscopic light absorptance and emission spectra of spatially inhomogeneous semiconductors. A model assuming a Gaussian distribution for the local band gaps yields closed-form expressions for the spectral absorptance and emission. Band gap fluctuations broaden the absorption edge of the fundamental band gap, as well as the associated emission peak. The spectral position of the photoluminescence emission peak depends on the length scale of the fluctuations in relation to the characteristic charge carrier transport length. We apply the model to experimental results from Cu(In1−x,Gax)Se2 thin films routinely used as photovoltaic absorbers in thin-film ZnO/CdS/Cu(In,Ga)Se2 heterojunction solar cells. The films feature band gap fluctuations with standard deviations between 15 and 65 meV which would lead to losses in the range of 5–80 mV for the open circuit voltage of solar cells made from these films. The pure ternary compounds CuInSe2 and CuGaSe2 exhibit smaller standard deviations than their quaternary alloys. This experimental finding indicates alloy disorder as one possible source of band gap inhomogeneities. The length scale of the observed fluctuations turns out to be much smaller than the minority carrier diffusion length. Hence, the band gap fluctuations occur on a length scale below 100 nm.

Ga Sb ∕ Ga As type II quantum dot solar cells for enhanced infrared spectral response

The authors report an enhanced infrared spectral response of GaAs-based solar cells that incorporate type II GaSb quantum dots (QDs) formed using interfacial misfit array growth mode. The material and devices, grown by molecular beam epitaxy, are characterized by current-voltage and spectral response characteristics. From 0.9to1.36μm, these solar cells show significantly more infrared response compared to reference GaAs cells and previously reported InAs QD solar cells. The short circuit current density and open circuit voltages of solar cells with and without dots measured under identical conditions are 1.29mA∕cm2, 0.37V and 1.17mA∕cm2, 0.6V, respectively.