Absorber For Perovskite Solar Cells Research Articles

Improvement efficiency of perovskite solar cells by hybrid electrospray and vapor-assisted solution technology

Abstract In this paper, we discuss the use of an electrospray method combined with a vapor-assisted solution technology (VAST) to prepare a perovskite solar cell absorber material. First, the PbI2 film was prepared using the electrospray method, and then through the VAST, the CH3NH3PbI3 perovskite absorber layer was formed, for which the device structure was ITO/PEDOT: PSS/CH3NH3PbI3/C60/BCP/Al. In the electrospray process, we changed the precursor solution concentration, voltage, and flow rate to control the thickness and surface morphology of the PbI2 film. In the VAST, we changed the CH3NH3I equivalent number and the heat treatment time, causing the CH3NH3I vapor deposited on the PbI2 film to form a CH3NH3PbI3 perovskite absorber layer. Finally, we completed the perovskite solar cell device. The power conversion efficiency (PCE) of the perovskite solar cell was 10.74%; the open circuit voltage (Voc) was 0.89 V; the short-circuit photocurrent (Jsc) was 21.30 mA/cm2, and the fill factor (FF) was 0.57.

First-principles study of intrinsic defects in formamidinium lead triiodide perovskite solar cell absorbers.

As an alternative to methylammonium lead triiodide (MAPbI3), formamidinium lead triiodide (FAPbI3) perovskites have recently attracted significant attention because of their higher stability and smaller band gaps. Here, based on first-principles calculations, we investigate systematically the intrinsic defects in FAPbI3. While methylammonium (MA)-related defects MAI and IMA in MAPbI3 have high formation energies, we found that formamidinium (FA)-related defects VFA, FAI and IFA in FAPbI3 have much lower formation energies. Antisites FAI and IFA create deep levels in the band gap, and they can act as recombination centers and result in reduced carrier lifetimes and low open circuit voltages in FAPbI3-based photovoltaic devices. We further demonstrate that through cation mixing of MA and FA in perovskites the formation of these defects can be substantially suppressed.

Potassium doped methylammonium lead iodide (MAPbI3) thin films as a potential absorber for perovskite solar cells; structural, morphological, electronic and optoelectric properties

In this article, we have demonstrated the doping of K in the light absorbing CH3NH3PbI3 perovskite i.e. (M = CH3, A = NH3; x = 0–1). One of the major merits of methylammonium lead iodide (CH3NH3PbI3) perovskites is that they act as efficient absorbing material of light in photovoltaic cell imparting long carrier lifetime and optimum band gap. The structural, morphological, electronic and optoelectric properties of potassium (K) doped light absorber methylammonium lead iodide (CH3NH3PbI3) perovskites are reported here i.e. Kx(MA)1−xPbI3 (M = CH3, A =NH3; x = 0–1). The thin films of perovskites (x = 0–1) were deposited by spin coating on cleaned FTO substrates and characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), current-voltage (IV), X-ray photoelectron spectroscopy (XPS) and Diffused reflectance spectroscopy (DRS) analysis. The organic constituents i.e. MA = CH3NH3, in perovskites solar cells induce instability even at the room temperature. To overcome such instabilities we have replaced the organic constituents by K because both of them have electropositive nature. Potassium successfully replaces the CH3NH3. Initially, this compound grows in a tetragonal crystal structure, however, beyond 30% doping of potassium orthorhombic distortions are induced in the parent tetragonal unit cell. Such phase transformation is microscopically visible in the electron micrographs of doped samples; cubic grains for MAPbI3 begin to transform into strip like structures in K-doped samples. The resistance of the samples is decreased for partial K-doping, which we suggested to be arising due to the electropositive nature of K. It is observed that the binding energy difference between Pb4f and I3d core levels are very similar in all the investigated systems and show formal oxidation states. Also, the partially doped samples showed increased absorption and bandgaps around 1.5eV which is an optimum value for solar absorption.

Progress and Prospect on Stability of Perovskite Photovoltaics

Solar energy has the potential to solve world energy problem as it is pollution- free. It could be enhanced using perovskite material as an absorber in perovskite solar cells. The history and what this material is made up of are emphasized. Different methods of fabrication, improving the power conversion efficiency (PCE) and factors influencing degradation of perovskite-based solar are stated. Because of the fact that this material based solar cells are not yet developed, its stability was reviewed to bring different technology employed in tackling the stability aiming for a better understanding of the material and the devices and facilitates the commercialization of perovskite solar cell.

Defect-Induced Band-Edge Reconstruction of a Bismuth-Halide Double Perovskite for Visible-Light Absorption.

Halide double perovskites have recently been developed as less toxic analogs of the lead perovskite solar-cell absorbers APbX3 (A = monovalent cation; X = Br or I). However, all known halide double perovskites have large bandgaps that afford weak visible-light absorption. The first halide double perovskite evaluated as an absorber, Cs2AgBiBr6 (1), has a bandgap of 1.95 eV. Here, we show that dilute alloying decreases 1's bandgap by ca. 0.5 eV. Importantly, time-resolved photoconductivity measurements reveal long-lived carriers with microsecond lifetimes in the alloyed material, which is very promising for photovoltaic applications. The alloyed perovskite described herein is the first double perovskite to show comparable bandgap energy and carrier lifetime to those of (CH3NH3)PbI3. By describing how energy- and symmetry-matched impurity orbitals, at low concentrations, dramatically alter 1's band edges, we open a potential pathway for the large and diverse family of halide double perovskites to compete with APbX3 absorbers.

Charge Carrier Trapping at Surface Defects of Perovskite Solar Cell Absorbers: A First-Principles Study.

The trapping of charge carriers at defects on surfaces or grain boundaries is detrimental for the performance of perovskite solar cells (PSCs). For example, it is the main limiting factor for carrier lifetime. Moreover, it causes hysteresis in the current-voltage curves, which is considered to be a serious issue for PSCs' operation. In this work, types of surface defects responsible for carrier trapping are clarified by a comprehensive first-principles investigation into surface defects of tetragonal CH3NH3PbI3 (MAPbI3). Considering defect formation energetics, it is proposed that a Pb-rich condition is preferred to an I-rich one; however, a moderate condition might possibly be the best choice. Our result paves the way for improving the performance of PSCs through a rational strategy of suppressing carrier trapping at surface defects.

Cesium lead iodide solar cells controlled by annealing temperature.

An inorganic lead halide perovskite film, CsPbI3, used as an absorber in perovskite solar cells (PSCs) was optimized by controlling the annealing temperature and the layer thickness. The CsPbI3 layer was synthesized by one-step coating of CsI mixed with PbI2 and a HI additive in N,N-dimethylformamide. The annealing temperature of the CsPbI3 film was varied from 80 to 120 °C for different durations and the thickness was controlled by changing the spin-coating rpm. After annealing the CsPbI3 layer at 100 °C under dark conditions for 10 min, a black phase of CsPbI3 was formed and the band gap was 1.69 eV. Most of the yellow spots disappeared, the surface coverage was almost 100%, and the rms roughness was minimized to 3.03 nm after annealing at 100 °C. The power conversion efficiency (PCE) of the CsPbI3 based PSC annealed at 100 °C was 4.88%. This high PCE value is attributed to the low yellow phase ratio, high surface coverage, low rms roughness, lower charge transport resistance, and lower charge accumulation. The loss ratio of the PCE of the CH3NH3PbIxCl3-x and CsPbI3 based PSCs after keeping in air was 47 and 26%, respectively, indicating that the stability of the CsPbI3 based PSC is better than that of the CH3NH3PbIxCl3-x based PSC. From these results, it is evident that CsPbI3 is a potential candidate for solar cell applications.

Circular Photogalvanic Effect in Organometal Halide Perovskite CH3NH3PbI3.

We study the circular photogalvanic effect in the organometal halide perovskite solar cell absorber CH3NH3PbI3. The calculated photocurrent density for a system with broken inversion symmetry is about 10-9 A/W, comparable to the previously studied quantum well and bulk Rashba systems. The circular photogalvanic effect relies on inversion symmetry breaking, so that by tuning the optical penetration depth, the degree of inversion symmetry breaking can be probed at different depths from the sample surface. We propose that measurements of this effect may clarify the presence or absence of inversion symmetry, which remains a controversial issue and has been argued to play an important role in the high conversion efficiency of this material.

Fabrication and Characterization of High Stability (EDA)(FA)$lt;inf$gt;2$lt;/inf$gt;[Pb$lt;inf$gt;3$lt;/inf$gt;I$lt;inf$gt;10$lt;/inf$gt;] Layered Perovskite Film

A new two-dimensional layered hybrid perovskite solar-cell absorber was synthesized by one-step method, using (EDA)I-2, (FA)I, and PbI2 with a 1 : 2 : 3 stoichiometric ratio in a solvent mixture of N, N-dimethylformamide(DMF). Ethylenediamine(EDA) cation was introduced into the perovskite lattice to synthesize a layered structure with improved resistance to the degradation by humidity in air. The effects of humidity and time on crystal structure, composition, morphology, and absorption spectra of (EDA)(FA)(2)[Pb3I10] and CH3NH3PbI3 were analyzed by in situ grazing incidence X-ray diffraction(GIXRD), X-ray diffraction (XRD), scanning electron microscope (SEM), atomic force microscope(AFM), and UV-Vis spectroscope. The results reveal that the prepared (EDA)(FA)(2)[Pb3I10] film is more moisture resistant than the CH3NH3PbI3 film which is widely used in the perovskite solar cell. SEM analysis reveals that the (EDA)(FA)(2)[Pb3I10] film has a layered structure, which can reduce the degradation caused by moisture. What's more, UV-Vis light absorption spectroscopy and atomic force microscopy(AFM) results show that the layered structure film is also a suitable absorber for perovskite solar cells. Photoluminescence spectrum(PL) reveals that bandgap of the (EDA)(FA)(2)[Pb3I10] film is 1.67 eV, which is close to the optimum value for solar photoelectric conversion. As compared to CH3NH3PbI3 film, the low-cost perovskite structure offers greater tunability on a molecular level for further material optimization and possibility for widely used in the future.

Electrodeposition of PbO and its in situ conversion to CH3NH3PbI3 for mesoscopic perovskite solar cells.

The perovskite CH3NH3PbI3 was prepared on a mesoscopic TiO2 film, starting from electrodepositing PbO, to iodination to PbI2, and then interdiffusion reaction with CH3NH3I. The as-prepared film was used as a light absorber for the perovskite solar cells, exhibiting a high PCE of 12.5% under standard AM 1.5 conditions.

A layered hybrid perovskite solar-cell absorber with enhanced moisture stability.

Two-dimensional hybrid perovskites are used as absorbers in solar cells. Our first-generation devices containing (PEA)2(MA)2[Pb3I10] (1; PEA=C6H5(CH2)2NH3(+), MA=CH3NH3(+)) show an open-circuit voltage of 1.18 V and a power conversion efficiency of 4.73%. The layered structure allows for high-quality films to be deposited through spin coating and high-temperature annealing is not required for device fabrication. The 3D perovskite (MA)[PbI3] (2) has recently been identified as a promising absorber for solar cells. However, its instability to moisture requires anhydrous processing and operating conditions. Films of 1 are more moisture resistant than films of 2 and devices containing 1 can be fabricated under ambient humidity levels. The larger bandgap of the 2D structure is also suitable as the higher bandgap absorber in a dual-absorber tandem device. Compared to 2, the layered perovskite structure may offer greater tunability at the molecular level for material optimization.

Efficient Planar Heterojunction Perovskite Solar Cells Based on Formamidinium Lead Bromide.

The development of medium-bandgap solar cell absorber materials is of interest for the design of devices such as tandem solar cells and building-integrated photovoltaics. The recently developed perovskite solar cells can be suitable candidates for these applications. At present, wide bandgap alkylammonium lead bromide perovskite absorbers require a high-temperature sintered mesoporous TiO2 photoanode in order to function efficiently, which makes them unsuitable for some of the above applications. Here, we present for the first time highly efficient wide bandgap planar heterojunction solar cells based on the structurally related formamidinium lead bromide. We show that this material exhibits much longer diffusion lengths of the photoexcited species than its methylammonium counterpart. This results in planar heterojunction solar cells exhibiting power conversion efficiencies approaching 7%. Hence, formamidinium lead bromide is a strong candidate as a wide bandgap absorber in perovskite solar cells.