Sn-based Perovskite Solar Cells Research Articles

Sn Perovskite Solar Cells via 2D/3D Bilayer Formation through a Sequential Vapor Process

Sn-based perovskite solar cells are attracting great attention because of their potential for efficiency enhancement and their relative eco-friendliness compared with Pb-based perovskite solar cell...

An optimized lead-free formamidinium Sn-based perovskite solar cell design for high power conversion efficiency by SCAPS simulation

Abstract An organic-inorganic perovskite formamidinium tin iodide (HC(NH2)2SnI3– FASnI3) is used as light absorbing layer in photovoltaics due to its lead-free nature, wider bandgap of 1.41 eV and better temperature stability than CH3NH3SnI3. In the present investigations, SCAPS simulation with comparison to the experimental as well as simulation data for FASnI3-based solar cell device is accomplished for high power conversion efficiency with proper optimization. The variation in the device design key parameters such as absorber, hole transport layer and electron transport layer thickness including defect density, doping concentration in absorber, carriers capture cross sections and interfacial defects are examined with their impact on device performance. The preliminary structure of device is based on the reported experimental and simulation work with the efficiency of 1.75% and 1.66%, respectively. After the SCAPS simulation with the optimization of basic parameters in this work, the final optimized performance parameters of the solar cell device are found to be enhanced with short-circuit current density (Jsc) of 31.20 mA/cm2, open-circuit voltage (Voc) of 1.81 V, fill factor (%FF) of 33.72% and power conversion efficiency (%PCE) of 19.08%.

Enhanced efficiency and stability in Sn-based perovskite solar cells with secondary crystallization growth

The conversion efficiencies reported for Tin (Sn) halide-based perovskite solar cells (PSCs) fall a large gap behind those of lead halide-based PSCs, mainly because of poor film quality of the former. Here we report an efficient strategy based on a simple secondary crystallization growth (SCG) technique to improve film quality for tin halide-based PSCs by applying a series of functional amine chlorides on the perovskite surface. They were discovered to enhance the film crystallinity and suppress the oxidation of Sn2+ remarkably, hence reduce trap state density and non-irradiative recombination in the absorber films. Furthermore, the SCG film holds the band levels matching better with carrier transport layers and herein favoring charge extraction at the device interfaces. Consequently, a champion device efficiency of 8.07% was achieved along with significant enhancements in Voc and Jsc, in contrast to 5.35% of the control device value. Moreover, the SCG film-based devices also exhibit superior stability comparing with the control one. This work explicitly paves a novel and general strategy for developing high performance lead-free PSCs.

Improving the Open-Circuit Voltage of Sn-Based Perovskite Solar Cells by Band Alignment at the Electron Transport Layer/Perovskite Layer Interface.

Organic-inorganic lead halide perovskites are promising materials for realization of low-cost and high-efficiency solar cells. Because of the toxicity of lead, Sn-based perovskite materials have been developed as alternatives to enable fabrication of Pb-free perovskite solar cells. However, the solar cell performance of Sn-based perovskite solar cells (Sn-PSCs) remains poor because of their large open-circuit voltage (VOC) loss. Sn-based perovskite materials have lower electron affinities than Pb-based perovskite materials, which result in larger conduction band offset (CBO) values at the interface between the Sn-based perovskite and a conventional electron transport layer (ETL) material such as TiO2. Herein, the relationship between the VOC and the CBO in these devices was studied to improve the solar cell performances of Sn-PSCs. It was found that the band offset at the ETL/perovskite layer interface affects the VOC of the Sn-PSCs significantly but does not affect that of the Pb-PSCs because the Sn-based perovskite material is a p-type semiconductor, unlike the Pb-based perovskite. It was also found that Nb2O5 has the CBO that is closest to zero for Sn-based perovskite materials, and the VOC values of Sn-PSCs that use Nb2O5 as their ETL are higher than those of Sn-PSCs using TiO2 or SnO2 ETLs. This study indicates that control of the energy alignment at the ETL/perovskite layer interface is an important factor in improving the VOC values of Sn-PSCs.

Enhanced Performance of Sn-Based Perovskite Solar Cells by Two-Dimensional Perovskite Doping

The poor performance of tin (Sn)-based perovskite solar cells (PSCs) is mainly due to the easy oxidation of Sn2+ to Sn4+, the low formation energy of Sn vacancies, and the unbalanced rates between ...

Bulky Cations Improve Band Alignment and Efficiency in Sn-Based Perovskite Solar Cells

The commercial feasibility of perovskite solar cells (PSCs) is not guaranteed as long as lead (Pb) is present in the active material, halide perovskites. Mixed halide Tin (Sn)-based alloyed perovskites with optimal band gaps ranging from 1.15 to 3.55 eV are excellent alternatives to Pb-based perovskites. In this work, we find that the addition of bulky phenylethyl ammonium (PEA) cation in the precursor solution leads to improved solar cell performance and optoelectronic properties. A prolonged laser exposure is found to induce a redshift the sample absorption for the control and no shift for the PEA-added sample, as shown by transient absorption spectroscopy. Further, we show that the addition of PEA improves band alignment of the perovskite with phenyl-C61-butyric acid methyl ester (PCBM), which aids in electron injection and therefore increases photocurrents in solar cells. These results show that PEA addition suppresses halide segregation improving material stability, charge collection at perovskite/electron transport layer, and recombination dynamics in perovskite material. As a result, the PEA-containing Sn-rich PSCs exhibited a champion efficiency of 13% with a high open-circuit voltage of 0.77 V and improved current-voltage hysteretic behavior. These results shed light on the importance of halide segregation and band alignment when designing lead-free PSCs.

4-Tert-butylpyridine-assisted low-cost and soluble copper phthalocyanine as dopant-free hole transport layer for efficient Pb- and Sn-based perovskite solar cells

The preparation of suitable hole transport material (HTM) is critical to the performance and stability of perovskite solar cells (PSCs) with low-cost. Herein, a mass producible and soluble copper phthalocyanine decorated with butoxy donor groups (CuPc-OBu) was designed as HTM and prepared by a facile two-step synthetic route. To generate high quality HTM film, 4-tert-butylpyridine (tBP) was doped into CuPc-OBu to prepare the film and then removed by annealing. Such a tBP-assisted strategy resulted in the best efficiency of the PSCs with lead trihalide perovskite up to 19.0% (small-area of 0.1 cm2) and 10.1% (the active area of 8.0 cm2 for the module device). And the best efficiency of the tin-based PSCs with CuPc-OBu reached to 6.9%. More importantly, the device with CuPc-OBu as HTM revealed the remarkably enhanced stability. This work provides a new strategy to improve the film-quality of free-doping HTMs and enhance the efficiency and stability of Pb- and Sn-based PSCs with low-cost.

Attenuating the defect activities with a rubidium additive for efficient and stable Sn-based halide perovskite solar cells

Rb incorporation in FASnI3 improved the device performance and stability as a consequence of the suppression of the extent of Sn2+ oxidation and mitigating defect activities.

Tuning cesium–guanidinium in formamidinium tin triiodide perovskites with an ethylenediammonium additive for efficient and stable lead-free perovskite solar cells

Utilizing cation tuning and implementing divalent cation hollowing and passivation to achieve efficient and stable pure Sn-based perovskite solar cells.

Efficient Anti-solvent-free Spin-Coated and Printed Sn-Perovskite Solar Cells with Crystal-Based Precursor Solutions

Summary Tin-based perovskite solar cells (PSCs), with more consummate optical band gaps, lower exciton-binding energies, and higher charge-carrier mobility, have not attracted tremendous research efforts compared with the lead-based ones that have a record power conversion efficiency (PCE) of 24.2%. The major challenges for Sn-based research are significantly low open-circuit voltage, poor reproducibility, and environmental instability. It has been identified that the oxidation processes take place during the preparation of precursor solutions and fabrication of films, due to the low redox potential of the stannous absorption layer. Herein, we propose two strategies of crystal-resolving and recrystallization technology to reduce the oxidation process. As a result, PCEs of 8.9% (active area of 0.04 cm2) and 5.5% (active area = 1.01 cm2) are attained using the inverted p-i-n structure, which will lead to a revival of lead-free PSC research.

Surface optimization by poly(α-methylstyrene) as additive in the antisolution to enhance lead-free Sn-based perovskite solar cells

Surface quality of the perovskite layer plays an important role in the determination of the device performance. This study presents an effective method to optimize the surface morphology for the lead-free formamidinium tin iodide (FASnI3) perovskite solar cells. Poly(α-methylstyrene) (PAMS) was applied as polymer additive into the diethyl ether at different blend concentration. The addition of PAMS can apparently reduce the pinholes at the surface of the FASnI3 film without ruining the interior crystallinity of the bulk FASnI3 layer. Therefore the non-radiative carrier traps can be effectively suppressed. The surface of the FAsnI3 film becomes more hydrophobic which facilitates the consequent spin-coating of the acceptor material solution. The modification of FASnI3 film’s wettability is favorable of the photo-induced carriers’ extraction and transportation. As a result, the power conversion efficiency of the PAMS-modified devices is greatly improved.

Simulation studies of non-toxic tin-based perovskites: Critical insights into solar performance kinetics through comparison with standard lead-based devices

Abstract We have simulated the operation and functionality of a working Sn-based perovskite solar cell device using GPVDM and compared it against a Pb-based device. The results are extremely promising in that they showcase comparable cell efficiencies, with the Sn-based device showing a highest 21.3% efficiency (Jsc of 332.8 A/m2, Voc of 0.839 V, FF of 0.764) compared to 23.4% of its Pb counterpart (Jsc of 349.3 A/m2, Voc of 0.811 V, FF of 0.828), at similar active layer thicknesses. A deeper study of each of the Jsc, Voc and FF trends provide keen insight into charge transfer kinetics within the device, paving the way to optimal experimental setups for fabricating the most efficient non-toxic perovskite devices.

Enhancing the crystallinity and perfecting the orientation of formamidinium tin iodide for highly efficient Sn-based perovskite solar cells

Low power conversion efficiency (PCE) and poor reproducibility are among the main challenges for tin-based perovskite solar cells (HPSCs). The facile formation of tin vacancies and oxidation of the divalent tin cation during the thin film fabrication process are among the causes of these problems, because the tin perovskite layer then becomes p-doped, resulting in significant trap-assisted recombination losses in devices. In this paper, we demonstrate that increasing the crystallinity of the tin perovskite film is an effective way to address the open issues with Sn-based perovskites. We succeed in improving the crystallinity of the 3D formamidinium tin iodide (FASnI3) grains, increasing their size, and perfecting their orientation in the out-of-plane direction by incorporating ethylammonium iodide (EAI) into a 2D/3D tin perovskite film (where 2D is PEA2FASn2I7, PEA = phenylethylammonium). This leads to a decrease of traps and background charge carrier density, and therefore to decreased charge recombination losses in EAx2D/3D based devices, as compared not only to devices based on FASnI3 but also to those based on 2D/3D mixtures. As a consequence, devices using a perovskite layer with composition EA0.082D/3D exhibit much higher PCE (8.4%) and better reproducibility compared to devices based on mixed 2D/3D perovskites (7.7%) and 3D perovskite (4.7%).

Tin(iv) dopant removal through anti-solvent engineering enabling tin based perovskite solar cells with high charge carrier mobilities

We report the need for careful selection of anti-solvents for Sn-based perovskite solar cells fabricated through the commonly used anti-solvent method, compared to their Pb-based counterparts.

Green Solution-Processed Tin-Based Perovskite Films for Lead-Free Planar Photovoltaic Devices.

The eco-friendly Sn-based perovskites have attracted more and more attention in lead-free perovskite photovoltaic field. However, the device performance and reproducibility are greatly challenged in preparing high-quality perovskite films. Here, we fabricated uniform and dense Sn-based perovskite films via a green gas pump treatment technology. Remarkably, we successfully fabricated a large-area (>20 cm2) Sn-based perovskite film with a mirror-like surface, which is the largest Sn-based perovskite film ever reported. Besides, we found that the phase separation phenomenon induced by excess SnF2 was eliminated when the pressure is 1500 Pa. Finally, we fabricated highly reproducible Sn-based solar cells and obtained an inspiring efficiency of 1.85%, which is the highest reported efficiency for Sn-based devices with a configuration of fluorine-doped tin oxide/compact TiO2/perovskite/hole transport material/electrode. Our results demonstrate the feasibility of using gas pump treatment technique to prepare high-quality Sn-based perovskite films, which paves a way for large-scale green manufacturing of Sn-based perovskite solar cells in the future.

Coadditive Engineering with 5-Ammonium Valeric Acid Iodide for Efficient and Stable Sn Perovskite Solar Cells

Sn-based perovskite solar cells (PSCs) featuring high performance and long-term stability are very challenging because Sn2+ is relatively prone to oxidation. Here, we have performed coadditive engineering with 5-ammonium valeric acid iodide (5-AVAI) for FASnI3-based perovskite films. From the morphological, structural, and elemental analyses, we observed that 5-AVAI affects the crystal growth of perovskites through its hydrogen bond with I– of the SnI64– octahedral. As a result, pinhole-free homogeneous and stable Sn-based perovskite films form over a large area with lower Sn4+ content. This made us able to enhance the power conversion efficiency (PCE) for Sn-based PSCs up to 7% in a 0.25 cm2 aperture area. Most importantly, the 5-AVAI added PSCs showed a record stability and maintained their initial PCE under 1 sun continuous illumination at maximum power point tracking for 100 h.

Stable Sn/Pb-Based Perovskite Solar Cells with a Coherent 2D/3D Interface

SummaryLow-band-gap metal halide perovskite semiconductor based on mixed Sn/Pb is a key component to realize high-efficiency tandem perovskite solar cells. However, the mixed perovskites are unstable in air due to the oxidation of Sn2+. To overcome the stability problem, we introduced N-(3-aminopropyl)-2-pyrrolidinone into the CH3NH3Sn0.5Pb0.5IxCl3-x thin film. The carbonyl group on the molecule interacts with Sn2+/Pb2+ by Lewis acid coordination, forming vertically oriented 2D layered perovskite. The 2D phase is seamlessly connected to the bulk perovskite crystal, with a lattice coherently extending across the two phases. Based on this 2D/3D hybrid structure, we assembled low-band-gap Sn-based perovskite solar cells with power conversion efficiency greater than 12%. The best device was among the most stable Sn-based organic-inorganic hybrid perovskite solar cells to date, keeping 90% of its initial performance at ambient condition without encapsulation, and more than 70% under continuous illumination in an N2-filled glovebox for over 1 month.

Solvent Engineering Improves Efficiency of Lead-Free Tin-Based Hybrid Perovskite Solar Cells beyond 9%

Here, we report on the effect of different antisolvent dripping on film morphology and charge recombination of mixed formamidinium–methylammonium tin iodide (FA0.75MA0.25SnI3) as a light absorber in perovskite solar cells. N,N-dimethyl methanamide (DMF) and dimethyl sulfoxide (DMSO) were used as the mixed solvent in the perovskite precursors together with tin fluoride (SnF2) as an additive. Diethyl ether (DE), toluene (TL), and chlorobenzene (CB) were employed as antisolvents for comparison. Our results show that CB as an antisolvent leads to a dense and uniform Sn-based perovskite film. The maximum power conversion efficiency of our Sn-based perovskite solar cell achieves 9.06% (9.02%) under forward (reverse) voltage scan under AM 1.5G 100 mW/cm2 illumination. The encapsulated cells show good long-term stability with ∼75% of their initial efficiency retained over a period of 30 days of storage. Our work suggests the promising potential to further improve the performance of Pb-free Sn-based perovskite sol...

"Unleaded" Perovskites: Status Quo and Future Prospects of Tin-Based Perovskite Solar Cells.

The tremendous interest focused on organic-inorganic halide perovskites since 2012 derives from their unique optical and electrical properties, which make them excellent photovoltaic materials. Pb-based halide perovskite solar cells, in particular, currently stand at a record efficiency of ≈23%, fulfilling their potential toward commercialization. However, because of the toxicity concerns of Pb-based perovskite solar cells, their market prospects are hindered. In principle, Pb can be replaced with other less-toxic, environmentally benign metals. Sn-based perovskites are thus the far most promising alternative due to their very similar and perhaps even superior semiconductor characteristics. After years of effort invested in Sn-based halide perovskites, sufficient breakthroughs have finally been achieved that make them the next runners up to the Pb halide perovskites. To help the reader better understand the nature of Sn-based halide perovskites, their optical and electrical properties are systematically discussed. Recent progress in Sn-based perovskite solar cells, focusing mainly on film fabrication methods and different device architectures, and highlighting roadblocks to progress and opportunities for future work are reviewed. Finally, a brief overview of mixed Sn/Pb-based systems with their anomalous yet beneficial optical trends are discussed. The current challenges and a future outlook for Sn-based perovskites are discussed.

Enhanced Photovoltaic Performance of FASnI3-Based Perovskite Solar Cells with Hydrazinium Chloride Coadditive

For the fabrication of efficient Sn-based perovskite solar cells (PSCs), deposition of uniform and pinhole-free perovskite films with low Sn4+ content remains a crucial factor. In this work, we present a coadditive engineering process by introduction of hydrazinium chloride (N2H5Cl) in a single precursor solvent system to fabricate FASnI3 perovskite films. The successful integration of N2H5Cl results in reduced concentration of Sn4+ content by 20% in the FASnI3 film leading to suppressed carrier recombination and pinhole-free uniform coverage. These remarkable improvements in the FASnI3 film results in power conversion efficiency (PCE) of Sn-based PSC up to 5.4% due to a significant increase in open-circuit voltage. Moreover, the best PSC without encapsulation showed stable shelf life up to 1000 h while retaining 65% of its initial PCE.