Characterization of high open-circuit voltage double sided buried contact (DSBC) silicon solar cells

The double sided buried contact (DSBC) silicon solar cells have consistently shown high open-circuit voltages (V_oc) than its single sided buried contact counterpart because of better rear surface passivation. The rear surface passivation which is provided by the rear floating junction is effective only when there is no leakage in the rear floating junction. However, the partial shunting of the rear floating junction can cause a drop in the fill factor of the cell which has been the only parameter limiting the realization of the structure's potentials. In this paper, LBIC (light beam induce current), spectral response, dark I-V and J_sc-V_oc measurements for DSBC cells have been carried out to help explain some of the experimentally observed attributes of this structure. The partly shunted rear floating junction has been identified by LBIC measurement as low current regions near the rear metal contacts.     

Low-energy proton irradiation effects on GaAs/Ge solar cells

This paper reports the low-energy proton irradiation effects on GaAs/Ge solar cells for space use. The proton irradiation experiments were performed with a fluence of 1.2×10¹³ cm⁻², energies ranging from 0.1 to 3.0 MeV. The results obtained demonstrate that the irradiation with a proton energy of 0.3 MeV gives rise to the most degradation rates of I_sc, V_oc and P_max of the solar cells with no coverglass, which is related to the proton irradiation-induced vacancies near the pn junction in GaAs/Ge cells. The degradation rates of I_sc, V_oc and P_max of the solar cells with coverglass increase as the proton energy increases due to the cascade ions induced by collision processes. It is found that the coverglass has an obvious protection effect against the irradiation with the proton energy below 0.5 MeV.     

Interface effects on the carrier transport and photovoltaic properties of hydrogenated amorphous silicon/crystalline silicon solar cells

Current-voltage-temperature (I-V-T) characteristics evaluated near 150K and 300K were used to study the photovoltaic property variations in hydrogenated amorphous silicon (a-Si:H)/crystalline silicon (c-Si) solar cells. The possible carrier transport mechanisms in such devices were examined from the I-V-T data which indicated a significant influence of the amorphous /crystalline interface on the short-circuit current density (J_sc) and open-circuit voltage (V_oc) of the solar cells. Carrier transport near 300K for forward biases was by a multi-tunneling mechanism and became space charge limited with increasing bias. For devices having low J_sc and V_oc an additional region was seen in both forward and reverse biases, at low temperatures, where the current simply varied linearly with the applied bias. This characteristic manifested in both high and low temperatures region for devices with still lower photovoltaic properties, which has been reasoned to be due to a higher interface density. Passivating the c-Si surface with HF just prior to the amorphous layer deposition resulted in a large improvement in the properties. The most significant effect was on the J_sc which improved by an order of magnitude. The treatment also affected the lower temperature I-V-T data in that the current fell to very low levels. The spectral response of the treated solar cells showed enhanced blue/violet response compared with the unpassivated devices. The interface passivation plus reducing a-Si thickness has improved the solar cell efficiency from 0.39% to 9.5%.     

Dependence of efficiency on slat angles of microgrooved solar cells

The short circuit current of a monocrystalline silicon solar cell can be enhanced further by suitably modifying the slat angle of its microgroove surface due to reduction in reflection coefficient and increase in optical trapping with decreasing slat angle. In this paper the dependence of I_sc, V_oc and η of a solar cell on the slat angle have been computed taking into account the variation of the reflection coefficient with the slat angle.It is observed that I_sc increases while V_oc decreases significantly with decreasing slat angles leading to a maximum efficiency of about 22% corresponding to a slat angle range lying between 30° and 45° without antireflection coating. However, the efficiency can be increased further to about 25% with AR coating.     

Influence of alkylaminopyridine additives in electrolytes on dye-sensitized solar cell performance

The influence of alkylaminopyridine additives on the performance of a bis(tetrabutylammonium)cis-bis(thiocyanato)bis(2,2′-bipyridine-4-carboxylic acid, 4′-carboxylate)ruthenium(II) dye-sensitized TiO₂ solar cell with an I⁻/I₃⁻ redox electrolyte in acetonitrile was studied. The current–voltage characteristics were measured for more than 20 different alkylaminopyridines under AM 1.5 (100 mW/cm²). The alkylaminopyridine additives tested had varying effects on the performance of the cell. All the additives decreased the short circuit photocurrent density (J_sc), but increased the open-circuit photovoltage (V_oc) of the solar cell. Molecular orbital calculations imply that the dipole moment of the alkylaminopyridine molecules influences the J_sc of the cell and that the size, solvent accessible surface area, and ionization energy all affect the V_oc of the cell. The highest V_oc of 0.88 V was observed in an electrolyte containing 4-pyrrolidinopyridine, which is comparable to the maximum V_oc of 0.9 V for a cell consisting of TiO₂ electrode and I⁻/I₃⁻ redox system.     

PECVD grown silicon nitride AR coatings on polycrystalline silicon solar cells

Silicon nitride films produced by plasma enhanced chemical vapor deposition (PECVD) have been studied as antireflection (AR) coating on polycrystalline silicon solar cells. A substantial enhancement (28%) in the short circuit current (I_sc) has been obtained. The open circuit voltage (V_oc) of these cells has also been found to improve after silicon nitride deposition. The deposition conditions to optimise the improvement in the cell performance have been discussed.     

5–20 MeV proton irradiation effects on GaAs/Ge solar cells for space use

This paper reports the high-energy proton irradiation effects on GaAs/Ge space solar cells. The solar cells were irradiated by protons with energy of 5–20 MeV at a fluence ranging from 1×10⁹ to 7×10¹³ cm⁻², and then their electric parameters were measured at AM0. It was shown that the I_sc, V_oc and P_max degrade as the fluence increases, respectively, but the degradation rates of I_sc, V_oc and P_max decrease as the proton energy increases, and the degradation is relative to proton irradiation-induced defect Ec−0.41 eV in irradiated GaAs/Ge cells.     

High-efficiency CIGS solar cells with modified CIGS surface

CIGS films were treated in In–S aqueous solution for high-efficiency CIGS solar cells. The In–S aqueous solution contained InCl₃ and CH₃CSNH₂ (thioacetamide). The In–S treatment modified the CIGS surface favorably for high-efficiency CIGS solar cells as evidenced by the increase in V_oc, J_sc and FF. The In–S treatment formed thin CuInS₂ layer on the CIGS surface which contributes to the high efficiency and stable performance of the CIGS solar cell. The best cell showed an efficiency of 17.6% (V_oc=0.649 V, J_sc=36.1 mA/cm² and FF=75.1%) without any annealing and light soaking before I–V measurement.     

Power output of Al/SnO2/n-Si solar cell

An Al/SnO₂/n-Si solar cell from n-type silicon (6.5 Ω-cm, 100) wafers using chemical vapour deposition (CVD) has been fabricated. The fabrication details, I–V characteristics determining conversion-efficiency (η_max), open circuit voltage (V_oc) and short circuit current (I_sc) have been presented. A maximum conversion efficiency of 6.3% for an unencapsulated cell of area 85.20 mm² has been obtained.     

Large-area high efficiency single crystalline silicon solar cells

This paper reports on a 100 cm² single crystalline silicon solar cell with a conversion efficiency of 19.44% (J_sc = 37.65 mA/cm², V_oc = 638 mV, FF = 0.809). The cell structure is as simple as only applying the textured surface, oxide passivation, and back surface field by the screen printing method. The comparison between cell performances of the CZ (Czochralski) and FZ (Floating zone) silicon substrates was investigated. The higher efficiency cells were obtained for the FZ substrate rather than the CZ substrate. The influence of the phosphorus concentration of the emitter on the cell efficiency has also been investigated. A good result was obtained when the surface concentration of phosphorus was 3 × 10²⁰ cm⁻³ and the junction depth was about 0.6 μm.     

Influence of pyrazole derivatives in I/I3 redox electrolyte solution on Ru(II)-dye-sensitized TiO2 solar cell performance

The influence of pyrazole additives in an I⁻/I₃⁻ redox electrolyte solution on the performance of a bis(tetrabutylammonium)cis-bis(thiocyanato)bis(2,2′-bipyridine-4-carboxylic acid, 4′-carboxylate)ruthenium(II) (N719) dye-sensitized TiO₂ solar cell was studied. The current–voltage characteristics of the cell were measured using 18 different pyrazole derivatives. All of the pyrazole additives enhanced the open-circuit photovoltage (V_oc) and the solar energy conversion efficiency (η), but reduced the short-circuit photocurrent density (J_sc). Most of the pyrazoles improved fill factor (ff). The physical and chemical properties of the pyrazoles were computationally calculated in order to elucidate the reasons for the additive effects on cell performance. The greater the partial charge of the nitrogen atom at position 2 in the pyrazole group, the larger the V_oc, but the smaller the J_sc values. As the dipole moment of the pyrazole derivatives increased, the V_oc value increased, but the J_sc value decreased. The V_oc of the cell also increased as the ionization energy of the pyrazoles decreased. These results suggest that the electron donicity of the pyrazole additives affected the interaction with the nanocrystalline TiO₂ photoelectrode, the I⁻/I₃⁻ electrolyte, and the acetonitrile solvent, which changed the Ru(II)-dye-sensitized solar cell performance.     

Radiation effects on fabricated Cu2S/CdS heterojunction photovoltaic cells

The photovoltaic properties including I–V characteristics, junction capacitance (C–V), short-circuit current (I_sc), open-circuit voltage (V_oc), fill factor (ff), efficiency (η), and spectral response of Cu₂S/CdS heterojunction cells have been examined before and after exposure to nuclear radiation. This included γ-rays of Co-60, and electron beams (at 1.5 MeV energy).The short-circuit current (I_sc) decreased, while the open-circuit voltage (V_oc), the fill factor (ff) and the efficiency (η) increased after heat treatment (at 260°C in air for 20 min). The I_sc effect during exposure to γ-rays was studied. It was found that I_sc increases as the dose rate increases. The sensitivity dependence of the I_sc density on dose rate was observed to be linear, and hence a universal constant for its sensitivity is found to be 45 (nA/cm²) (rad/s).No permanent damage was shown until about 300 Mrad for γ rays and 380 Mrad for electron beams. After these doses, the I_sc and V_oc slightly decreased on increasing the absorbed dose.After heat treatment, the spectral response was modulated. It was found that the wavelength response against the photocurrent decreased from 1000 to 800 nm and the photocurrent also slightly decreased in the range of wavelengths from 800 to 450 nm and increased from 350 to 540 nm. Heat treatment before irradiation improved the photovoltaic cells. After irradiation by γ-rays and electron beams, the photocurrent went back to its original value by annealing (for 2 h at 500°C). The capacitance–voltage behavior decreased after irradiation and hence the doping decreased.     

Influence of alkyl dihalide gelators on solidification of dye-sensitized solar cells

Quasi-dye-sensitized solar cells were prepared by using ionic liquid-type electrolytes and gelators consisting of polyvinylpyridine and alkyl dihalides. Gelation occurred by the reaction of polyvinylpyridine and alkyl dihalides. When the chain length of the dihalides was varied, the short-circuit current (J_sc) increased with an increase in the chain length. However, the open-circuit voltage (V_oc) and fill factor (ff) slightly decreased. The increase in J_sc was brought about by the decrease in the interfacial resistances between the gel electrolyte and the counter electrode. In addition, the increase in the J_sc was explained by increases in the apparent diffusion coefficient of I⁻/I₃⁻ when the chain length increased. Decreases in V_oc and ff were explained by back-electron transfers from TiO₂ to iodine in the electrolytes. V_oc of the cells solidified by alkyldiiodide was lower than that solidified by alkyldichloride or alkyldibromide. It was explained by negatively shifted redox potential of I⁻/I₃⁻, compared with those for Cl⁻/Cl₂ or Br⁻/Br₂.     

Influence of aminothiazole additives in I/I3 redox electrolyte solution on Ru(II)-dye-sensitized nanocrystalline TiO2 solar cell performance

The influence of aminothiazole additives in acetonitrile solution of an I⁻/I₃⁻ redox electrolyte on the performance of a bis(tetrabutylammonium)cis-bis(thiocyanato)bis(2,2′- bipyridine-4-carboxylic acid, 4′-carboxylate)ruthenium(II) (N719) dye-sensitized TiO₂ solar cell was studied. The current–voltage characteristics were investigated under AM 1.5 (100 mW/cm²) for nine different aminothiazole compounds. The aminothiazole additives tested had varying influences on the solar cell performance. Most of the additives enhanced the open-circuit photovoltage (V_oc), but reduced the short circuit photocurrent density (J_sc) of the solar cell. Both the physical and chemical properties of the aminothiazoles were computationally calculated in order to determine the reasons that the additive influenced solar cell performance. The larger the calculated partial charge of the nitrogen atom in the thiazole, the higher the V_oc value. The V_oc value increased as the dipole moment of aminothiazoles in acetonitrile increased. Moreover, the V_oc of the solar cell also increased as the size of the aminothiazole molecules decreased. These results suggest that the electron donicity of the aminothiazole additives influenced the interaction with the TiO₂ photoelectrode, which altered the dye-sensitized solar cell performance.     

Influence of alkylpyridine additives in electrolyte solution on the performance of dye-sensitized solar cell

The influence of alkylpyridines additive to an I⁻/I₃⁻ redox electrolyte in acetonitrile on the performance of a bis(tetrabutylammonium)cis-bis(thiocyanato)bis(2,2′-bipyridine-4-carboxylic acid, 4′-carboxylate)ruthenium(II) dye-sensitized TiO₂ solar cell was studied. I–V measurements were performed using more than 30 different alkylpyridines. The alkylpyridine additives showed a significant influence on the performance of the cell. All the additives decreased the short-circuit photocurrent (J_sc), but most of the alkylpyridines increased the open-circuit photovoltage (V_oc) and fill factor (ff) of the solar cell. The results of the molecular orbital calculations suggest that the dipole moment of the alkylpyridine molecules correlate with the J_sc of the cell. These results also suggest that both the size and ionization energy of pyridines correlate with the V_oc of the cell. Under AM 1.5 (100 mW/cm²), the highest solar energy conversion efficiency (η) of 7.6% was achieved by using 2-propylpyridine as an additive, which was more effective than the previously reported additive, 4-t-butylpyridine.     

Electrodeposition zinc-oxide inverse opal and its application in hybrid photovoltaics

This article reports the preparation of three-dimensional (3D) mesoporous zinc oxide (ZnO) films and their application in solar cells. The films were obtained through electrochemical deposition in DMSO solutions by using PS colloidal crystal as templates. The ZnO films with inverse opal (IO) structure were obtained after removing the templates by thermolysis. The ordered porous ZnO films were used to prepare hybrid solar cells by infiltrating the films with poly(3-hexylthiophene) (P3HT) or P3HT:ZnO nanocomposite. Results showed that the interpenetrating network of both ZnO(IO) and P3HT can form continuous pathways for electron and hole transport. By infiltrating a P3HT:ZnO nanocomposite into the porous ZnO films, the photocurrent of the solar cell can be dramatically improved. The cell shows the V_oc and I_sc of 462 mV and 444.3 μA/cm², respectively. By using a 420 nm cutoff filter, the cell retains about 80% and 50% of its original V_oc and I_sc after continuous white-light illumination (100 mW/cm²) for 10 h. Stability of the device under above conditions was estimated to be 51 h.     

Determination of the electrical characteristics and thermal behaviour of a c-Si cell under transient conditions for various concentration ratios

An extended study of c-Si cell performance under transient conditions for various concentration ratios, C, between 0.6 and 12.25 is presented. PV cell temperature, T_c, open-circuit voltage, V_oc, and short-circuit current, I_sc, were measured using an experimental set-up based on a solar light simulator. The dependence of V_oc, I_sc, dV_oc/dT_c, dI_sc/dT_c and r_s on T_c was investigated against C. A model was developed to predict T_c. Generalised formulae were proposed for prediction of V_oc and I_sc. Theoretically obtained T_c and V_oc profiles were compared with the measured ones. A good agreement was observed. The time constants of V_oc and T_c profiles were determined experimentally for various C values and lie within ±5% from theoretically predicted time constants. The coefficient dV_oc/dT_c was determined for various C values. The results show a decrease in the absolute value of dV_oc/dT_c against C. A partial recovery of PV cell performance through a ventilation process was tried.     

Photovoltaic characteristics of CuInS2/CdS solar cell by electron beam evaporation

When a CuInS₂/CdS solar cell was fabricated by depositing CdS thin film with dopant In of 1.0 at% on ternary compound CuInS₂ thin film with the lowest resistivity of 5.59 × 10⁻² Ωcm, its best result was as follows: V_oc = 461 mV, I_sc = 26.9 mA, FF = 0.685, η = 5.66% under the illumination of 100 mW/cm². And its series resistance and lattice mismatch was 5.1 Ω and 3.2%, respectively.Besides, a 4 layer structure solar cell of -CuInS₂/high -CuInS₂/high -CdS/low - CdS has been fabricated. When thickness of high - CuInS₂ was 0.2 μm, its best result was as follows: V_oc = 580 mV, I_sc = 30.6 mA, FF = 0.697, η = 8.25%. An its series resistance and lattice mismatch were 4.3 Ω and 2.8%, respectively.     

The infrared processing in multicrystalline silicon solar cell low-cost technology

New directions in photovoltaics depend very often on financial possibilities and new equipment. In this paper, we present the modification of a standard screen-printing technology by using an infrared (IR) furnace for forming a n⁺/p structure with phosphorus-doped silica paste on 100 cm² multicrystalline silicon wafers. The solar cells were fabricated on 300 μm thick 1 Ω cm p-type multicrystalline Bayer silicon. The average results for 100 cm² multicrystalline silicon solar cells are: I_sc=2589 mA, V_oc=599 mV, FF=0.74, E_ff=11.5%. The cross-sections of the contacts metallized in the IR furnace, as determined by scanning electron microscopy, and the phosphorus profile measured by an electrochemical profiler are shown. IR processing offers many advantages, such as a small overall thermal budget, low power and time consumption, in terms of a cost-effective technology for the continuous preparation of solar cells.     

Wafer thickness, texture and performance of multi-crystalline silicon solar cells

The influence of wafer thickness and surface texturing of silicon solar cells on cell results has been investigated using neighbouring multi-crystalline silicon wafers with thickness ranging from 150 to 350 μm and isotropic NaOH or acid etched. It was found experimentally that V_oc decreases nearly 1.5% and J_sc decreases nearly 3%, resulting in a 4% relative decrease in efficiency, in halving the wafer thickness. These trends are independent of the front surface texturing.Front surface texturing, however, results in a 6% increase of J_sc and a nearly 6% increase in efficiency independent of the wafer thickness.