Perovskite Cells Research Articles

Regulating Energy Loss in Perovskite Cells

Regulating Energy Loss in Perovskite Cells

Large organic cations are beneficial for slowing tin-based perovskites crystallization rate and improving efficiency

In the past few years, the efficiency of perovskite cells has been improved rapidly, and the current efficiency can reach 25.8%. Since the lead in perovskite materials will pollute the environment, so people turn their attention to lead-free tin-based perovskites. Tin-based perovskites are becoming a research hotspot recently due to their nontoxic properties. However, due to the fast crystallization rate of tin-based perovskite, the improvement of the efficiency of tin-based perovskite cells is limited. In this work, by introducing ethylammonium iodine (EAI) into FA0.98SnI3 perovskite, it not only slowed down the crystallization rate of tin-based perovskite cells, but also improved the film morphology and slowed down the rate of Sn2+ oxidation, and finally achieved a solar cell conversion efficiency of 7.6%. This work provides a new strategy for the study of lead-free perovskites.

A Comparison of Spectrum-Splitting Configurations for High-Efficiency Photovoltaic Systems With Perovskite Cells

The recent development of inexpensive perovskite photovoltaic (PV) cells at a variety of band gap energies has opened the prospects for commercially viable spectrum-splitting PV systems. A variety of cell configurations exist for implementing spectrum splitting in PV modules. In this article, 3-junction and 4-junction hybrid spectrum-splitting systems are proposed that use volume holographic lens arrays for lateral spectral separation and absorptive filtering in semitransparent perovskite PV cells for vertical spectral separation. A 3-junction hybrid system is shown to have greater conversion efficiency (28.7%) than comparable systems using completely lateral (25.6%) or completely stacked (26.9%) cell arrangements. It is shown that a 4-junction hybrid system has a hypothetical conversion efficiency of 30.0% using perovskite PV cells that have been experimentally demonstrated in the literature with energy band gaps of 1.25 eV, 1.55 eV, 1.72 eV, and 2.30 eV.

Theoretical analysis of all-inorganic solar cells based on numerical simulation of CsGeI3/CsPbI3 with p-p+ built-in electric field

With the development of perovskite solar cells (PSCs) technology, inorganic perovskite led by CsPbI3 gradually shows the photovoltaic performance of organic perovskite cells. However, this is still based on the organic charge transport layer. CsPbI3 with all-inorganic structure still need to be further studied. Therefore, in this study, an all inorganic CsGeI3/CsPbI3 laminated structure with CsGeI3 instead of organic HTL is introduced, and numerical simulation is carried out through SCAPS-1D (Solar Cells Capability Simulator). It is found that the two perovskite layers, which are both p-type materials, have shown excellent efficiency in the p-p+ built-in electric field. In this paper, PSCs are optimized with absorbing layer thickness, doping concentration, defect density, metal electrode work function and so on. The best thickness is determined according to the different light absorption properties of Pb2+ and Ge2+, and the toxicity of the original single-layer lead based perovskite is reduced. Through the comprehensive analysis of band bending, built-in electric field and recombination rate, we explained the reason why the parameters increase with the growth of doping concentration (NA). In terms of NA regulation, it is found through simulation that when NA of the two absorption layers is at 1015 to 1018 cm−3, the photogenerated carriers are driven by the strong p-p+ built-in electric field to migrate well in the flat energy band, which significantly improves the photovoltaic performance of PSCs. For the defect density the charge transport layer, the PSC absorption characteristics, and the metal electrodes, we made a choice based on the photovoltaic performance and process level. Finally, the power conversion efficiency of the optimized PSCs reached 24.06 % and the fill factor is 86.19 %. This study proved that p-p+ structure constructed by lead germanium mixed metal has great potential for inorganic perovskite solar cells with Cs as a cation in the future.

Impact of mixed perovskite composition based silicon tandem PV devices on efficiency limits and global performance

Optical and electrical features of halide perovskites make them commercially attractive high-efficiency solar cell absorbers. As a result, perovskite/silicon tandem solar cells have recently garnered the scientific community’s attention due to their better efficiency than single-junction solar cells. The most researched perovskite solar cell (PSC) is based on methylammonium lead iodide perovskite type; nevertheless, mixed cation/anion perovskites show better performances. Compositional engineering of perovskite allows us to screen for more efficient and stable materials. To better understand perovskite/silicon tandem performance, we systematically analyse the impact of compositions on device output under standard testing conditions and real-world climate using an opto-thermal model. Regional cell temperature and energy yield potential for variable perovskite compositions and bandgaps, FAxMA(1−x)Pb(BryI(1−y))3, are investigated. The optimal band gaps for bottom cells using Si (1.12 eV) and perovskite top cells (around 1.5–2.1 eV) are studied for realistic climate conditions. With a bandgap of 1.7 eV, the compound MAPbBrI 2 exhibited the best opto-electronic performance in tandem cells. Globally, Perovskite/silicon tandem cells (except 2.1 eV top cell perovskite) performed thermally better than Silicon solar cells due to the increased efficiency of tandem devices. The world-wide average perovskite cell temperature reduction was −3.9 °C, whereas the average energy generated was 26.7% higher relative to silicon solar cells. The current study will be extended by analysing the temperature coefficient’s sensitivity and employing realistic solar cell architectures.

Photovoltaic Materials and Their Path toward Cleaner Energy.

Photovoltaic silicon converts sunlight in 95% of the operational commercial solar cells and has the potential to become a leading material in harvesting energy from renewable sources, but silicon can hardly convert clean energy due to technologies required for its reduction from sand and further purification. The implementation of the novel materials into photovoltaic systems depends on their conversion efficiency limited by the material's inherent properties, longevity dependent on internal stability, and ease of manufacturing process. A major challenge is discovering a multilayered set of different photovoltaic materials capable of converting clean energy from a wider spectra range since emerging materials and technologies such as dye-sensitized and quantum dots suffer from low conversion efficiencies while perovskite and organic cells have short longevity in atmospheric conditions. Presently, improving technologies for commercialized materials and creating multijunction solar cells enhanced by new photovoltaic materials is a path toward cleaner energies. With the rapid development of the integrative technologies and challenges that photovoltaics for clean energy conversion are facing, the entire clean photovoltaic industry could arise by bottom-up course as a part of integrative technologies rather than erecting large power plants.

Chelate Coordination Strengthens Surface Termination to Attain High-Efficiency Perovskite Solar Cells.

Solar cell efficiency and stability are two key metrics to determine whether a photovoltaic device is viable for commercial applications. The surface termination of the perovskite layer plays a pivotal role in not only the photoelectric conversion efficiency (PCE) but also the stability of assembled perovskite solar cells (PSCs). Herein, a strong chelate coordination bond is designed to terminate the surface of the perovskite absorber layer. On the one hand, the ligand anions bind with Pb cations via a bidentate chelating bond to restrict the ion migration, and the chelate surface termination changes the surface from hydrophilic to hydrophobic. Both are beneficial to improving the long-term stability. On the other hand, the formation of the chelating bonding effectively eliminates the deep-level defects including PbI and Pb clusters on the Pb-I and FA-I terminations, respectively, as confirmed by theoretical simulation and experimental results. Consequently, the PCE is increased to 24.52%, open circuit voltage to 1.19V, and fill factor to 81.53%; all three are among the highest for hybrid perovskite cells. The present strategy provides a straightforward means to enhance both the PCE and long-term stability of PSCs.

Cooperative Adsorption of Metal-organic Complexes on CsPbI2 Br Perovskite Surface for Photovoltaic Efficiency Exceeding 17 .

Inorganic perovskite solar cells have attracted wide attention due to their excellent thermodynamic stability and suitable bandgap as the top absorber materials for tandem solar cells. However, the power conversion efficiencies (PCEs) of the perovskite cells can be considerably limited by the non-radiative energy loss caused by grain boundaries and surfaces. Here, the synergistic functionalization of CsPbI2 Br perovskites was demonstrated by using a metal-organic complex. Experimental and theoretical studies revealed that the adsorption energy of the passivator could be a good descriptor to evaluate the surface passivation effect. The cooperative adsorption could eliminate the unsaturated surface sites, reduce the surface energy, and thus benefit device performance. The CsPbI2 Br solar cells passivated by zinc diethyldithiocarbamate showed a champion power conversion efficiency of 17.15 % and retained 94 % of their initial efficiency after working under 1 sun illumination for 720 h in N2 atmosphere.

Plated copper electrodes for two-terminal perovskite/silicon tandem solar cells

Electroplated copper electrodes are manufactured for the first time on 22.5 cm2 two-terminal perovskite/silicon tandem solar cells. This study demonstrates that a 10 nm thin atomic layer deposited (ALD) Al2O3 masking layer on ITO enables the tandem cells to withstand the chemistry of the wet chemical metallization process. Our approach uses a screen-printed Ag seed-layer on ITO for homogeneous electroplating current distribution and a photoconversion efficiency up to ≈ 15% is reached. To avoid the use of any metal seed-layer on ITO, we also demonstrate a light-induced Cu plating (LIP) process. This further validates the presence of an electrical contact between the Cu electrode and both perovskite and Si cells. Finally, progress with the transfer of the native oxide barrier layer for selective electroplating (NOBLE) metallization to bifacial perovskite/silicon tandem solar cells is presented.

Inhibiting the Growth of 1D Intermediates in Quasi‐2D Ruddlesden−Popper Perovskites

AbstractQuasi‐2D perovskite solar cells have recently emerged as a highly prospective and inexpensive solution for sustainable energy due to their intrinsic optoelectronic properties and stability. The qualities of these promising quasi‐2D perovskite cells are generally affected by different intermediates derived from the precursor solution during film fabrication processing. However, efficient solutions to inhibit intermediates remain insufficient to date. Here, an effective strategy is prsented to inhibit the growth of 1D solvate intermediate during the fabricating process of quasi‐2D perovskite films by introducing a guanidinium thiocyanate (GUASCN) inhibitor. Theoretical calculations reveal that the SCN− anions spontaneously replace the iodide ions in the inorganic framework [PbI6]3− and induce the decomposition of the solvate intermediate. The resulted perovskite solar cells exhibit a significant improvement in power conversion efficiency (PCE), benefiting from the reduced trap‐state density and enhanced carrier mobilities. The unencapsulated devices retain 91% and 95% of the original PCEs under 45 ± 10% humidity in air or under continuous light irradiation at 100 mW cm−2 and 45 °C in a nitrogen atmosphere for 1000 h. Particularly, devices without electron‐transporting layers maintain 85% of the peak PCE under maximum power point tracking at 45 °C for 1000 h.

Theoretical Modeling of Perovskite–Kesterite Tandem Solar Cells for Optimal Photovoltaic Performance

Herein, a solar cell device simulation study is performed using the solar cell capacitance simulator 1D tool to assess the performance parameters of a monolithic two‐terminal (2‐T) and a mechanically stacked four‐terminal (4‐T) tandem solar cell with a top perovskite subcell and a bottom subcell consisting of a perovskite material FA0.83Cs0.17PbI1.5Br1.5 and a kesterite photovoltaic material Cu2ZnSnSe4 as the light‐harvesting material, respectively. The 2‐T tandem device design furnishes a open‐circuit voltage, short‐circuit current density, fill factor, and power conversion efficiency (PCE) of 1.81 V, 18.18 mA cm−2, 66.18%, and 31.15%, respectively, while establishing the condition of matching the short‐circuit current density between the top perovskite and bottom kesterite cells. The 4‐T device furnishes a high PCE of 37.49% when the filtered spectrum is used for modeling the bottom subcell. Further, the optimization of the input parameters of the light active layers of the top and bottom cells leads to an increase in PCE of the 4‐T tandem device to 37.84%.

A Geometrically Well-Defined and Systematically Tunable Experimental Model to Transition from Planar to Mesoporous Perovskite Solar Cells.

A series of perovskite solar cells with systematically varying surface area of the interface between n-type electron conducting layer (TiO2) and perovskite are prepared by using an ordered array of straight, cylindrical nanopores generated by anodizing an aluminum layer evaporated onto a transparent conducting electrode. A series of samples with pore length varied from 100 to 500 nm are compared to each other and complemented by a classical planar cell and a mesoporous counterpart. All samples are characterized in terms of morphology, chemistry, optical properties, and performance. All samples absorb light to the same degree, and the increased interface area does not generate enhanced recombination. However, the short circuit current density increases monotonically with the specific surface area, indicating improved charge extraction efficiency. The importance of the slow interfacial rearrangement of ions associated with planar perovskite cells is shown to decrease in a systematic manner as the interfacial surface area increases. The results demonstrate that planar and mesoporous cells obey to the same physical principles and differ from each other quantitatively, not qualitatively. Additionally, the study shows that a significantly lower TiO2 surface area compared to mesoporous TiO2 is needed for an equal charge extraction.

Performance of planar perovskite solar cells based on formamidinium cations: Simulation and fabrication

The best efficiency ever recorded for state-of-the-art perovskite solar cells (PSCs) is about 25% where the formamidinium (FA)-dominated perovskites were adopted. But the optimum content of FA perovskite solar cells based on Cs0.05(FAxMA[1−x])0.95Pb(I0.83Br0.17)3 films has yet to materialize the high-power conversion efficiency. Herein, high quality and uniform perovskite films constituting Cs-MA-FA (Cesium; Methylammonium) mixed cation in the A-site of the ABX3 structure with different FA content are synthesized by a typical spin coating based antisolvent technique. Because of the limitations of perovskite and solar cell materials, the influences of various FAs on the device performance are analyzed through device simulation. From the synthesized films, the band gap equation of Cs0.05(FAxMA[1−x])0.95Pb(I0.83Br0.17)3 has been estimated, ranging from 2.175 eV to 1.5 eV for various FA/(FA + MA) ratios respectively. Ultimately, the highest conversion efficiency of the planar solar cell based on graded perovskite with various FA content was obtained for the case where the positive Eg grading consists of the Eg of 2.175 eV at the front (FA/[FA + MA] of 0) and the Eg of 1.5 eV at the back (FA/[FA + MA] of 1). The Cs0.05(FA0.87MA0.13)0.95Pb(I0.83Br0.17)3 cell achieved an AM1.5G conversion efficiency of around 20.98%, showing improved VOC, JSC, and FF among the planar perovskite solar cells with different x.

Reducing electrical losses of textured monolithic perovskite/silicon tandem solar cells by tailoring nanocrystalline silicon tunneling recombination junction

Compatible with crystalline silicon industry standards, thermal evaporation of perovskite cells on fully textured wafers with noticeable light trapping has been established. Then perovskite/silicon tandem solar cells prepared by this method presented potentially high photocurrent, but their open-circuit voltage ( V oc ) and fill factor (FF) were moderate. Here, electrical losses of perovskite/silicon tandem solar cells were reduced through combining the theoretical model of tunneling recombination junction (TRJ) with the growth mechanism of nanocrystalline silicon films. Their V oc loss was compensated 38 mV (from 1.767 V to 1.805 V), and FF was increased from 64.29% to 74.15% via adjusting the transport and recombination of carriers in TRJ. The fully textured tandem solar cell exhibited an efficiency of 26.91%, which provided an approach towards tandem devices with more than 30% efficiency. • The theoretical model of TRJ and the growth mechanism of nanocrystalline silicon films were both combined to reduce electrical losses. • The V oc gain reached 38 mV (from 1.767V to 1.805V), and the FF was increased from 64.29% to 74.15% for tandem device. • The PCE of champion tandem solar cell reached 26.91%.

Progress on strategies to control the built-in electric field of perovskite solar cells

<p indent="0mm">Perovskite solar cells (PSCs) are high-efficiency and low-cost photovoltaic devices that have been extensively studied by researchers around the world. The carrier separation and transport inside the solar cell is the key process of the device operation, which is directly related to the photoelectric conversion efficiency (PCE) of the device. The built-in electric field formed by the heterojunction dominates the behavior of carriers, and its strength determines the separation efficiency of electrons and holes in the device. Therefore, regulating and optimizing the built-in electric field can fundamentally improve the performance of the solar cells. Much work is focusing on the built-in electric field for the fabrication of high-efficiency devices. According to previous results, this paper firstly introduces some fundamental experiments on the heterojunctions and the mechanism of carrier separation and transport of PSCs. Secondly, the regulation strategies of the built-in electric field commonly used in perovskite solar cells and their effects on device performance are summarized. The following are the most common built-in electric field control strategies: (1) Tuning the built-in electric field of perovskite solar cells by doping. The method of doping to control the built-in electric field is to add appropriate impurities according to different conductive properties of the materials. According to the structure of planar perovskite solar cells, doping the electron transport layer, hole transport layer, and perovskite layer of PSCs with different doping materials can change the position of the Fermi level and further enlarge the splitting of the Fermi level which can assist in the separation and transport of carriers. (2) Tuning the built-in electric field of perovskite cells by constructing 3D/2D perovskite heterojunctions. Fabrication of 3D/2D heterojunctions can not only improve the PCE of perovskite solar cells, but also improve its stability, so this method is more popular among researchers. The construction of 3D/2D perovskite heterojunctions can expand the splitting of the Fermi level to form a more powerful built-in electric field. This method can increase the separation and transport efficiency of carriers, and improve the PCE and open the circuit voltage of the device. (3) Tuning the built-in electric field of perovskite cells by constructing a dipole layer. Electric dipoles have the property of changing the work function of materials. Using them can effectively adjust the energy level structure of perovskite solar cells, expand the work function difference, and increase the built-in electric field strength to achieve the effect of enhancing carrier separation and transport efficiency. The above three methods are relatively popular control strategies for the built-in electric field of perovskite solar cells and this paper systematically analyzes and summarizes them. In the end, we evaluate the built-in electric field regulation technologies of perovskite solar cells, and look forward to the future development of this field. Enhancing the built-in electric field of perovskite solar cells is the key to improving the PCE of the device. In the future, more research should be devoted to the study of the built-in electric field of perovskite solar cells.

Performance and stability enhancement of mixed dimensional bilayer inverted perovskite (BA2PbI4/MAPbI3) solar cell using drift-diffusion model

A variety of classic photovoltaic technologies, such as multi-crystal silicon and copper indium gallium selenide, have been exceeded by organometal halide perovskite solar cells, which have made significant advancements in the cost-effective manufacturing method as well as the high power conversion efficiency. Meanwhile, the unfavourable operational stability of perovskite solar cells is impeding the commercialization of the technology. When exposed to critical environmental factors such as rising moisture and intense sunlight, perovskite solar cells suffer lattice degradation and lose their ability to harvest energy. As a result, enhancing the stability of perovskite cells is one of the most important variables in determining the next wave of progress for the technology. While there have been numerous techniques reported to improve the stability of perovskite-based photovoltaic cell, the construction of a more than one dimension (2D/3D) perovskite as the light absorbing layer has recently emerged as one of the most reliable strategies to stabilise the perovskite-based device without compromising photo physical performance. Herein, we have computationally simulated p-i-n device configuration composed of ITO/NiO/2D perovskite/3D perovskite/PCBM/Au. The Ruddlesden-Popper (RP) phases of two-dimensional perovskite act as a cover layer, which inhibits the deterioration of 3D perovskite in an open-air environment. Both optical and electrical simulation is performed using solar cell capacitance simulator (SCAPS). Simulation findings showed that the enhancements in overall performance are due to the decrease in the trap state's density and better coordination of the band between the 2D/3D perovskite and the hole-transporting materials. Effects of the interfacial defects (2D perovskite/HTL and 3D perovskite/ETL) on solar cell parameters are also performed. Simulation results reveal that the defects at 3D perovskite/ETL interfacial are more dominating in overall performance degradation. Parametric differences, such as thickness of various layers, standard solar spectra, further refine the proposed architecture. The multidimensional-based architecture proposed in this work resulted in a power conversion efficiency (PCE) of 19.6%.

Intensity Modulated Photocurrent Microspectrosopy for Next Generation Photovoltaics.

In this report, a large-area laser beam induced current microscope that has been adapted to perform intensity modulated photocurrent spectroscopy (IMPS) in an imaging mode is described. Microscopy-based IMPS method provides a spatial resolution of the frequency domain response of the solar cell, allowing correlation of the optoelectronic response with a particular interface, bulk material, specific transport layer, or transport parameter. The system is applied to study degradation effects in back-contact perovskite cells where it is found to readily differentiate areas based on their markedly different frequency response. Using the diffusion-recombination model, the IMPS response is modeled for a sandwich structure and extended for the special case of lateral diffusion in a back-contact cell. In the low-frequency limit, the model is used to calculate spatial maps of the carrier ambipolar diffusion length. The observed frequency response of IMPS images is then discussed.

Modelling tandem/multi-junction hybrid perovskite–organic solar cells: A combined drift–diffusion and kinetic Monte Carlo study

Hybrid Organic–inorganic semiconductors are an excellent option for developing photovoltaic devices because of their broad range of bandgaps, inexpensive deposition techniques, and broad solar spectrum absorption. Perovskite–organic tandem solar cells with two terminals (2T) have emerged as the potential architectures to reach high efficiency. Several device characteristics like thickness and bandgaps of the sub-cells must be optimized to maximize solar spectrum utilization in a 2T tandem cell. This study proposes a multiscale simulation model for tandem/multi-junction architecture using hybrid perovskite–organic solar cells. Initially, tandem architecture using perovskite absorbers and organic blend is modelled to explore the series-connected tandem solar cell structure and analyse the effect on the device performance. We observe that the implemented perovskite–organic tandem architecture can achieve high efficiency of 19.8%. This work further explores different perovskite cells combined with the organic blend in a multi-junction configuration to cover the broad solar spectrum with as high as 25.2% power conversion efficiency. In turn, this gives a concrete model representation that can help optimize the device architecture leading to high-efficiency hybrid perovskite–organic devices.

Cation‐Diffusion‐Based Simultaneous Bulk and Surface Passivations for High Bandgap Inverted Perovskite Solar Cell Producing Record Fill Factor and Efficiency

AbstractHigh bandgap perovskite solar cells are integral to perovskite‐based multi‐junction tandem solar cells with efficiency potentials over 40%. However, at present, high bandgap perovskite devices underperform compared to their mid bandgap counterparts in terms of voltage outputs and fill factors resulting in lower than ideal efficiencies. Here, the low fill factor aspect of high bandgap perovskite is addressed by developing a cation‐diffusion‐based double‐sided interface passivation scheme that simultaneously provides bulk passivation for a 1.75 eV perovskite cell that is also compatible with a p‐i‐n cell architecture. The champion cell achieves a record fill factor of 86.5% and a power conversion efficiency of 20.2%. Results of ionic distribution profiling, Fourier transform infrared spectroscopy, and X‐ray diffraction crystallography reveal evidence of cation diffusion from the surface perovskite passivation layer into bulk. The diffused cations reduce Shockley–Read–Hall recombination in the perovskite bulk and at the surfaces with the latter being more dominant as confirmed by light‐intensity dependent and temperature‐dependent open‐circuit voltage measurements as well as thermal admittance spectroscopy. This concurrent bulk and surface passivation scheme renders record fill factor and efficiency in the double‐side passivated cells. This provides new insights for future passivation strategies based on ionic diffusion of functionalized materials.

Optoelectronic modeling of all-perovskite tandem solar cells with design rules to achieve &gt;30% efficiency

All-perovskite tandem solar cells pave the way for increasing the efficiency of solar cells beyond the Shockley-Queisser limit imposed on single junction perovskite cells. While all-perovskite tandem solar cells with high power conversion efficiency (PCE) of 24.8% have been fabricated, the understanding of the underlying device physics during their operation still remains unclear. In this work we present an optoelectronic model for monolithic all-perovskite tandem solar cell. This coupled model incorporating transfer matrix model for optical effects, and drift diffusion model for electrical effects accurately describes the photophysical and optoelectronic processes occurring in the all-perovskite tandem cell. The results of this model have been verified with results from a recent published experimental work on all-perovskite tandem cell with 24% PCE and show good agreement. The key parameters governing the PCE of tandem solar cells, such as trap density in active layer, recombination layer resistance, carrier mobility and absorber layer thicknesses are evaluated to establish design rules to attain greater than 30% PCE for all-perovskite tandem solar cells. Even though this model has been developed for an all-perovskite tandem solar cell, the principle guiding the model is general and can be applied to any type of tandem photovoltaic technology.