Benefit of Grain Boundaries in Organic-Inorganic Halide Planar Perovskite Solar Cells.

In recent times, planar organo-metal halide perovskite solar cells (PSCs) achieved high power conversion efficiency (PCE > 22%). Mixed organic-inorganic halide perovskites, with excellent light harvesting properties, have evolved as a promising class of semiconductors for photovoltaics. In this work, compositional and electrical characterizations of materials used for different layers of PSC have been studied. One dimensional solar cell simulator wx-AMPS is used for numerical simulation of such devices and all simulations are done under AM1.5 illuminations and 300K temperature. Investigating the influences of thickness of electron transport material (ETM), hole transporting material (HTM) and absorber on the photovoltaic performance of PSCs, it is observed that, increase in thickness of perovskite (MAPbI3) results in the increase in PCE of solar cells, whereas increase in thickness of ETM layer results in decrease in the efficiency of the devices. The ETM plays a vital role on the performance of PSC. In this paper, for the first time performances of PSC for three different ETMs (TiO2, ZnO or SnO2) are calculated and analyzed simultaneously with the simulator wx-AMPS. The photovoltaic performances have been explored and efficiencies of 27.6%, 27.5% and 28.02% are reported for perovskite solar cells with TiO2, ZnO and SnO2 as ETM respectively for a specific thickness. Finally, this simulation study concludes that ZnO and SnO2 may be effective alternatives of the commonly used material, TiO2 as they are economically more potential and give somewhat better photovoltaic performance.
 Dhaka Univ. J. Sci. 66(2): 109-114, 2018 (July)

The key progress in the development of solar cells based on mixed organic-inorganic halide perovskite was reviewed. Perovskite solar cells (PSCs) have developed rapidly and achieved highest efficiency exceeding 20% in these years. The origin, working principle and fabrication technology of PSCs are stated, and several promising methods to realize the industrialization of the solar cell modules have been put forward. Meanwhile, two main problems existing in PSCs have been pointed out, hysteresis in the photocurrent density-voltage measurement and the instability of perovskite, which have impacted the application of PSCs seriously. Efforts and study in order to solve these problems are also listed. The fundamental mechanism still needs further investigation so as to improve the performance of PSCs and realize their large-scale application eventually.

Effect on the morphology and optical properties of CH3NH3PbI3 with additive of NH4Cl

Heterojunction and sandwich architectures are two new-type structures with great potential for solar cells. Specifically, the heterojunction structure possesses the advantages of efficient charge separation but suffers from band offset and large interface recombination; the sandwich configuration is favorable for transferring carriers but requires complex fabrication process. Here, we have designed two thin-film polycrystalline solar cells with novel structures: sandwich CIGS and heterojunction perovskite, referring to the advantages of the architectures of sandwich perovskite (standard) and heterojunction CIGS (standard) solar cells, respectively. A reliable simulation software wxAMPS is used to investigate their inherent characteristics with variation of the thickness and doping density of absorber layer. The results reveal that sandwich CIGS solar cell is able to exhibit an optimized efficiency of 20.7%, which is much higher than the standard heterojunction CIGS structure (18.48%). The heterojunction perovskite solar cell can be more efficient employing thick and doped perovskite films (16.9%) than these typically utilizing thin and weak-doping/intrinsic perovskite films (9.6%). This concept of structure modulation proves to be useful and can be applicable for other solar cells.

ABSTRACTThe Polycrystalline Thin Film Solar Cells Program, part of the United States National Photovoltaic Program, performs R&D on copper indium diselenide and cadmium telluride thin films. The objective of the Program is to support research to develop cells and modules that meet the U.S. Department of Energy's long-term goals by achieving high efficiencies (15% - 20%), low-cost ($50/M2), and long-time reliability (30 years). The importance of work in this area is due to the fact that the polycrystalline thin-film CuInSe2 and CdTe solar cells and modules have made rapid advances. They have become the leading thin films for PV in terms of efficiency and stability. The U.S. Department of Energy has increased its funding through an initiative through the Solar Energy Research Institute in CuInSe2and CdTe with subcontracts to start in Spring 1990.

The halogen chemistry of halide perovskites

Lead-free organic inorganic hybrid halide perovskites: An emerging candidate for bifunctional applications

The past two years have seen the uniquely rapid emergence of a new class of solar-cell-based on mixed organic-inorganic halide perovskite. In this work, we demonstrate a promising technique for studying the morphology of perovskite and its impact on carrier extraction by carrier transport layer using one-photon and two-photon fluorescence imaging in conjunction with time-resolved photoluminescence. This technique is not only effective in separating surface and bulk effects but it also allows the determination of lifetimes in localized regions and local carrier extraction efficiency. The difference in sensitivities of transport materials to grain boundaries and film uniformity is highlighted in this study. It is shown that the PCBM fabricated in this work is more sensitive to film nonuniformity, whereas spiro-OMeTAD is more sensitive to grain boundaries in terms of effective carrier extraction.

The past two years have seen the uniquely rapid emergence of a new class of solar-cell-based on mixed organic-inorganic halide perovskite. In this work, we demonstrate a promising technique for studying the morphology of perovskite and its impact on carrier extraction by carrier transport layer using one-photon and two-photon fluorescence imaging in conjunction with time-resolved photoluminescence. This technique is not only effective in separating surface and bulk effects but it also allows the determination of lifetimes in localized regions and local carrier extraction efficiency. The difference in sensitivities of transport materials to grain boundaries and film uniformity is highlighted in this study. It is shown that the PCBM fabricated in this work is more sensitive to film nonuniformity, whereas spiro-OMeTAD is more sensitive to grain boundaries in terms of effective carrier extraction.

Diversifying Progress in Solar

In this paper, the effects of different CdCl2 annealing methods, including vapor annealing and dip-coating annealing, on the performance of CdS/CdTe polycrystalline thin-film solar cells are studied. After annealing, the samples are lightly etched with 1% bromine in methanol to remove surface oxides. Both annealing methods give CdTe polycrystalline thin films with good crystallinity and complete structure. For solar cells containing the annealed CdTe films, cell efficiency first increases and then decreases as the concentration of CdCl2 solution used for dip-coating annealing increases, and the optimized CdCl2 concentration is 12%. The uniformity of the performance of all cells is analyzed by calculating the relative standard deviation for each parameter. The uniformity of cell performance can be improved dramatically by dip-coating annealing instead of vapor annealing. Most notably, an appropriate concentration of CdCl2 (12%) acts as a protective layer that is conducive to realizing uniform high-performance CdS/CdTe solar cells. According to the location of depletion regions, the CdTe films treated by dip-coating annealing show a relatively low doping concentration, except for the sample treated with a CdCl2 concentration of 6%, which is consistent with the changes of short-circuit current density of the cells. It is believed that these results can be applied to the large-scale production of CdTe polycrystalline thin-film solar cells.

The objective of the thin film polycrystalline solar cell work in the U.S.A. is to develop thin film materials which have potential for achieving thin film array efficiencies of greater than 10% at a price of $100-300/kW <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e</inf> . A variety of thin film materials and technologies are presently being researched to determine their potential for solar cell conversion and low cost fabrication. The materials being investigated include CdS, GaAs, Si, amorphous Si, InP, CdTe, Zn <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> P <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> , ZnSiAs, and Cu <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> O. Homojunction, heterojunction, Schottky barrier and conductive oxides are being studied as collection barriers for efficient solar cell conversion. The variety of solar cell research areas will be reviewed describing the technologies being pursued, the results obtained, and the important problems or issues to be resolved.

ABX3 Perovskites for Tandem Solar Cells

In this work, compact titanitum dioxide (c-TiO2), amorphous titanitum dioxide (mp-TiO2) and methylammonium lead iodide (CH3NH3PbI3) films were prepared by spin coating method under different different rotational speed of the CH3NH3PbI3 films. Many characterization measurements were achieved on the deposited CH3NH3PbI3 films in order to study the change that resulted from different parameters. The X-ray diffraction (XRD) measurements revealed that the lattice constants of the fabricated CH3NH3PbI3 films were close to the slandered values. The atomic force microscopy (AFM) measurements were conducted in order to study the morphology of the fabricated CH3NH3PbI3 films at different scale, these results displayed that the grain size of the CH3NH3PbI3 films in the range between about 160nm to 210 nm. The field emiision scanning electron microscopy (FE-SEM) results of the fabricated CH3NH3PbI3 films were well agreed to the AFM result especially in the grains shape and distribution. Transmittance measurements have been done to determine the variation of the energy gap and absorption coefficient the CH3NH3PbI3 films. The structure form of the perovskite solar cells were FTO/c-TiO2/mp- TiO2/CH3NH3PbI3/Au, the C-V measurements were achieved to determine the built-in potential, which found to have the highest value when using 4000 rpm during the synthesis of the perovskite layer. In addition, the I-V measurements in dark conditions have been conducted to compute the ideality factor and the saturation current, which are considered important parameters that influences the characteristics of the solar cells. The best solar cell efficiency was obtained at spinning speed of 4000 rpm.

Controlled phase separation for efficient energy conversion in dye/polymer blend bulk heterojunction photovoltaic cells