Photoconversion Efficiency Of Solar Cells Research Articles

Improved Photoresponse in Association with a Synthesized Dielectric Material for Quantum Dots Solar Cells

A worldwide investigation is being carried out for improving the photoconversion efficiency of solar cells. Among all solar cells, quantum dots solar cell (QDSC) has proven as the best potential for photocurrent generator. The major focus of this research work is comparing the performance of QD based solar cells with and without the addition of synthesized dielectric nanomaterials for reducing recombination problems and higher the exciton generation. The selection of dielectric nanomaterial was carried out based on their good field-effect passivation, screened columbic attraction, enactment as a back reflector, and recombination inhibitor in solar cell. According to the above-mentioned factors lanthanum doped lead titanate Pb0.85La0.15TiO3 (PLT15) is a promising material for this research work. For improving the performance of QD based solar cells, the PLT15 paired mesoporous TiO2 electron transport layer (ETL) film was deposited onto fluorine-doped tin oxide (FTO) coated glass substrate using doctor blading technique followed by annealing the QD deposition onto the coated glass substrate was carried out via dipping of the glass into the QD solution for overnight. The QD used in this research work were namely – PbI3. Finally, the performance study was carried out which indicates that the introduction of dielectric material into the QDSC has proven to be as innovative and as well as efficient for improving the photocurrent conversion efficiency.

Structural, Magnetic Properties and Dye-Sensitized Solar Cells Application of Pure and La Doped BiFeO3 Powders Prepared by Sol-Gel

Multifunctional materials Bi1-xLaxFeO3 (x = 0.05, 0.10, 0.15, 0.20) powders with and without annealing (700°C) were prepared by sol-gel method to improve the magnetic and optical properties. The particle size, chemical structures, and chemical compositions of the powders were investigated by bright-field TEM, XRD, SADP, and XRF. The bright-field TEM results show the particle size of the prepared Bi1-xLaxFeO3 powders without annealing (around 200 nm) is less than that of the annealed Bi1-xLaxFeO3 powders (more than 500 nm). The XRD results of the powders without annealing show the formation of rhombohedral structure of BiFeO3 with Bi24Fe2O39 as impurity phase in all samples, whereas the prepared powders annealed at 700°C have a higher phase purity. The M – H hysteresis loop of the powders with annealing and without annealing were measured by vibrating sample magnetometer at room temperature up to the field of 10 kOe. The results demonstrate that the powders with higher purity phase and larger particle size were larger saturation magnetization. The saturation magnetizations were increased by increasing the La doping content. The optical absorption edge result can be considered energy band gap (∼2.0–2.2 eV) of all prepared powders. The prepared powders were used as photoelectrode in dye-sensitized solar cell applications. The current density versus voltage characteristics of solar cell were measured under illumination of simulated sunlight coming from a solar simulator with the radiant power of 100 mW/cm2 to obtain photocurrent, photovoltage, and overall photoconversion efficiency of solar cells. The power conversion, photocurrent density and photovoltage depending on purity, particle size with and without annealing powders using as photoelectrode in dye sensitized solar cells are discussed.

Electron Injection Dynamics at the SILAR Deposited CdS Quantum Dot/TiO2 Interface

Semiconductor quantum dots with their tunable band gap energies offer new opportunities for controlling photoresponse and photoconversion efficiency of solar cells. Exciton dissociation, charge injection, and charge recombination are key steps for efficient interfacial electron transfer. Here, electron injection and carrier relaxation dynamics at the CdS quantum dot/TiO2 interface were investigated by using ultrafast transient absorption spectroscopy and global fitting analyses. The CdS/TiO2 composites were prepared by depositing CdS in the TiO2 nanocrystalline films by the successive ionic layer adsorption and reaction (SILAR) technique. Comparing the transient absorption spectra of CdS/TiO2 composites formed by different numbers of CdS coating cycles and CdS/Al2O3 revealed size-dependent electron injection from excited CdS into TiO2 nanoparticles, which occurred on a time scale of 1–9 ps. We also demonstrated that holes are trapped in a localized state with a time constant of 0.3 ps, which was faster th...

Ab Initio Simulation of Charge Transfer at the Semiconductor Quantum Dot/TiO2 Interface in Quantum Dot‐Sensitized Solar Cells

Quantum dot‐sensitized solar cells (QDSSCs) have emerged as a promising solar architecture for next‐generation solar cells. The QDSSCs exhibit a remarkably fast electron transfer from the quantum dot (QD) donor to the TiO2 acceptor with size quantization properties of QDs that allows for the modulation of band energies to control photoresponse and photoconversion efficiency of solar cells. To understand the mechanisms that underpin this rapid charge transfer, the electronic properties of CdSe and PbSe QDs with different sizes on the TiO2 substrate are simulated using a rigorous ab initio density functional method. This method capitalizes on localized orbital basis set, which is computationally less intensive. Quite intriguingly, a remarkable set of electron bridging states between QDs and TiO2 occurring via the strong bonding between the conduction bands of QDs and TiO2 is revealed. Such bridging states account for the fast adiabatic charge transfer from the QD donor to the TiO2 acceptor, and may be a general feature for strongly coupled donor/acceptor systems. All the QDs/TiO2 systems exhibit type II band alignments, with conduction band offsets that increase with the decrease in QD size. This facilitates the charge transfer from QDs donors to TiO2 acceptors and explains the dependence of the increased charge transfer rate with the decreased QD size.

Simulation of solar cells with quantum wells and comparison with conventional solar cells

The efficiency of photoconversion in solar cells based on GaAs with InGaAs quantum wells under the AM 1.5 conditions for various levels of base doping has been simulated using the software package Sim-Windows. The results obtained are compared with the efficiency of photoconversion in conventional solar cells. It is shown that solar cells with quantum wells can exhibit a fairly high efficiency of photoconversion in comparison with the photoconversion efficiency of conventional solar cells under the following conditions: (i) the lifetimes of for charge carriers in the quantum wells are longer than those in the barrier material and (ii) the level of doping of the base is not very high. It is established that the maximum efficiency of photoconversion in conventional solar cells is higher than the photoconversion efficiency in solar cells with quantum wells. This efficiency is attained at high doping levels in the base (∼3 × 1018 cm−3 at the parameters used in calculations). This is related to a more intense radiative recombination and also to specific features of screening and charge transport in solar cells with quantum wells at high doping levels. It is shown that, at fairly large values for the degree of concentration of incident radiation, the values for the photoconversion efficiency in solar cells with quantum wells for the low and high levels of doping of the base come closer to each other.

Photoluminescence enhancement induced by nanoparticles from La 2O 3 and CeO 2 doped diamond-like carbon films

La 2O 3 and CeO 2 doped composite hydrogen-free diamond-like carbon (DLC) films with thickness of 230–280 nm were deposited by unbalanced magnetron sputtering. Nanoparticles are formed on the surface of deposited films. Auger electron spectroscopy shows the C, O, La and Ce elements distribute uniformly along the depth direction, and they diffuse into the Si(1 0 0) substrate. X-ray photoelectron spectroscopy confirms the forming of La 2O 3 and CeO 2 within the DLC films, and the amorphous DLC structure is not changed with the doping of rare earth oxides. G peak positions shift to higher wave numbers, and relative intensities ratio I D/ I G increase of DLC films with the doping of La 2O 3 and CeO 2, indicating the coherence between the I D/ I G and G peak position. Furthermore, the photoluminescence (PL) obviously increase with the forming of nanoparticles and doping of La 2O 3 and CeO 2. Specially, the PL intensity of 4% La 2O 3 and 4% CeO 2 doped composite DLC films is 18.4 times of that of pure DLC films, which is beneficial for the increase of photoconversion efficiency of solar cells.