Robust Tin-Based Perovskite Solar Cells with Hybrid Organic Cations to Attain Efficiency Approaching 10.

Tin-based perovskite solar cells have gained global research attention due to the lead toxicity and health risk associated with its lead-based analog. The promising opto-electrical properties of the Tin-based perovskite have attracted researchers to work on developing Tin-based perovskite solar cells with higher efficiencies comparable to lead-based analogs. Tin-based perovskites outperform lead-based ones in areas such as optimal band gap and carrier mobility. A detailed understanding of the effects of each parameter and working conditions on Tin-based perovskite is crucial in order to improve efficiency. In the present work, we have carried out a numerical simulation of a planar heterojunction Tin-based (CH3NH3SnI3) perovskite solar cell employing a SCAPS 1D simulator. Device parameters, namely, the thickness of the absorber layer, the defect density of the absorber layer, working temperature, series resistance, and metalwork function, were exclusively investigated. ZnO was employed as the ETL (electron transport layer) material in the initial simulation to obtain optimized parameters and attained a maximum efficiency of 19.62% with 1.1089 V open circuit potential (Voc) at 700 nm thickness (absorber layer). Further, different ETL materials were introduced into the optimized device architecture, and the Zn2SnO4-based device delivered an efficiency of 24.3% with a Voc of 1.1857 V. The obtained results indicate a strong possibility to model and construct better-performing perovskite solar cells based on Tin (Sn) with Zn2SnO4 as the ETL layer.

Lead-free tin perovskite solar cells

Tin-based halide perovskite compounds have attracted enormous interest as effective replacements for the conventional lead halide perovskite solar cells (PCSs). However, achieving high efficiency for tin-based perovskite solar cells is still challenging. Herein, we introduced copper sulfide (CuS) as a hole transport material (HTM) in lead free tin-based B-γ-CsSnI3 PSCs to enhance the photovoltaic (PV) performances. The lead free tin-based CsSnI3 perovskite solar cell structure consisting of CuS/CsSnI3/TiO2/ITO was modeled and the output characteristics were investigated by using the one dimensional solar cell capacitance simulator (SCAPS-1D). The CuS hole transport layer (HTL) with proper band arrangement may notably minimize the recombination of the charge carrier at the back side of the perovskite absorber. Density functional theory (DFT)-extracted physical parameters including the band gap and absorption spectrum of CuS were used in the SCAPS-1D program to analyze the characteristics of the proposed PV device. The PV performance parameters of the proposed device were numerically evaluated by varying the absorber thickness and doping concentration. In this work, the variation of the functional temperature on the cell outputs was also studied. Furthermore, different HTMs were employed to investigate the PV characteristics of the proposed CsSnI3 PSC. The power conversion efficiency (PCE) of ~29% was achieved with open circuit voltage (Voc) of 0.99 V, a fill factor of ~87%, and short circuit current density (Jsc) of 33.5 mA/cm2 for the optimized device. This work addressed guidelines and introduced a convenient approach to design and fabricate highly efficient, inexpensive, and stable lead free tin-based perovskite solar cells.

Decoupling the effects of defects on efficiency and stability through phosphonates in stable halide perovskite solar cells

The performance of four distinct materials (organic and inorganic) was simulated and analyzed as hole transport layer (HTL) in the design of germanium (Ge)-based Perovskite Solar Cell (PSC). A 1-dimensional numerical software (SCAPS 1-D) has been applied to simulate the HTL candidates: spiro-OMeTAD, PTAA, nickel oxide (NiO), and copper (I) thiocyanate (CuSCN), with tin (IV) dioxide (SnO2) as the electron transport layer (ETL). The thickness of the methylammonium germanium iodide (CH3NH3GeI3) absorber was varied from 300 nm to 1100 nm, and the highest simulated power conversion efficiency was achieved at a thickness of 800 nm for all HTL candidates. It was observed that the inorganic CuSCN outperformed its counterparts with a power conversion efficiency (PCE) of 25.38%. The effect of the perovskite absorber’s defect density was investigated, and ultimately, it was demonstrated that this value is disproportionately related to the PCE. A reduction of nearly 98% in PCE was recorded when the defect density increased from 1x1014 cm-3 to 1x1020 cm-3. Additionally, for a constant ETL thickness of 80 nm, it was revealed that the PCE would decrease slightly, ranging from 0.1% to 0.3%, with an increase in HTL thickness from 50 nm to 300 nm. Comparing the PCE of our current work with published reports further justifies its competitiveness. Full Text: PDF References W.R. Becquerel, "Becquerel Photovoltaic Effect in Binary Compounds", J. Chem. Phys. 32, 1505 (1960). CrossRef A. Kojima, K. Teshima, Y. Shirai, T. Miyasaka, "Organometal Halide Perovskites as Visible-Light Sensitizers for Photovoltaic Cells", J. Am. Chem. Soc. 131, 6050 (2009). CrossRef M.M. Salah, K.M. Hassan, M. Abouelatta, A. Shaker, "A comparative study of different ETMs in perovskite solar cell with inorganic copper iodide as HTM", Optik 178, 958 (2019). CrossRef S. Rai, B. Pandey, A. Garg, D. Dwivedi, "Hole transporting layer optimization for an efficient lead-free double perovskite solar cell by numerical simulation", Opt. Mater, 121, 111645 (2021). CrossRef H. Liangsheng, Z. Min, S. Yubao, M. Xinxia, W. Jiang, Z. Qunzhi, F, Zaiguo, L. Yihao, H. Guoyu, L. Tong, "Tin-based perovskite solar cells: Further improve the performance of the electron transport layer-free structure by device simulation", Sol. Energy, 230, 345 (2021). CrossRef K. Fatema, M. Arefin, "Enhancing the efficiency of Pb-based and Sn-based perovskite solar cell by applying different ETL and HTL using SCAPS-ID", Opt. Mater. 125, 112036 (2022). CrossRef P. Patel, "Device simulation of highly efficient eco-friendly CH3NH3SnI3 perovskite solar cell", Sci. Rep., 11, 3082 (2021). CrossRef P. Roy, Y. Raoui, A. Khare, "Design and simulation of efficient tin based perovskite solar cells through optimization of selective layers: Theoretical insights", Opt. Mater., 125, 112057 (2022). CrossRef A.I. Azmi, M.Y. Mohd Noor, M.H.I. Ibrahim, F. Ahmad, M.H. Ibrahim, "A Numerical Simulation of Transport Layer Thickness Effect in Tin-Based Perovskite Solar Cell", JJEE, 8, 355 (2022). CrossRef A.A. Kanoun, M.B. Kanoun, A.E. Merad, S. Goumri-Said, "Toward development of high-performance perovskite solar cells based on CH3NH3GeI3 using computational approach", Sol. Energy, 182, 237 (2019). CrossRef A. Hima, N. Lakhdar, "Enhancement of efficiency and stability of CH3NH3GeI3 solar cells with CuSbS2", Opt. Mater., 99, 109607 (2020). CrossRef S.T. Jan, M. Noman, "Influence of layer thickness, defect density, doping concentration, interface defects, work function, working temperature and reflecting coating on lead-free perovskite solar cell", Sol. Energy, 237, 29 (2022). CrossRef

High-performance methylammonium-free ideal-band-gap perovskite solar cells

ABX<sub>3</sub> crystalline perovskite material has many advantages: good photoelectric absorption property, high charge carrier mobility, good film formation, long charge carrier lifetime, and easy bandgap adjustment for absorption layer of perovskite solar cells. As a result, the power conversion efficiency (PCE) of the organic-inorganic halide perovskite solar cells (PSCs) has taken a tremendous step forward, from 3.9% in 2009 to a recently reported value over 25.5%. Thus, it shows great potential to compete with traditional silicon solar cells. However, PSCs preparing conditions are harsh and susceptible to environmental influences, thus leading to instability. Therefore, it is essential to prepare high-performance and stable PSCs in an air environment. This study aims to use the ion doping method to improve the performance and stability of PSCs and analyze the mechanism. This work focuses on enhancing PSCs efficiency and stability by performing FA<sup>+</sup> and Cl<sup>–</sup> doping experiments on MAPbI<sub>3</sub> films in air. The results show that a single Cl<sup>–</sup>-doping increases the carrier diffusion length, reducing the recombination of electrons and holes, and inducing the perovskite intermediate hydrate (CH<sub>3</sub>NH<sub>3</sub>)<sub>4</sub>PbI<sub>6</sub>·2H<sub>2</sub>O to form, promoting the crystallization of the thin film, and improving the device performance. On the other hand, a single FA<sup>+</sup>-doping will reduce the bandgap of perovskite and increase the short-circuit current density (<i>J</i><sub>SC</sub>) of the device, and FA<sup>+</sup> is susceptible to the influence of water vapor to induce a yellow <i>δ</i>-FAPbI<sub>3</sub> perovskite film to form, which leads the device performance to degrade. However, the prepared co-doping Cl<sup>–</sup>, FA<sup>+</sup> significantly improves overall PSCs device performance, yielding the highest PCE of 17.29%, and showing excellent stability by maintaining over 80% of the original PCE without any encapsulation after 1000-hour storage in ambient air.

Revealing phase evolution mechanism for stabilizing formamidinium-based lead halide perovskites by a key intermediate phase

This report computationally investigates the relative influence of absorber layer crystallinity and the nature of interfaces in lead-based (toxic) and tin-based (non-toxic) perovskite solar cells using SCAPS-1D. The absorber layer crystallinity was modelled in terms of varying charge carrier mobility and defect density while the interfacial behaviour was modelled through varying defect density at the electron transport material (ETM)/perovskite and perovskite/hole transport material (HTM) interfaces. The results suggest that tuning of the aforementioned parameters plays a critical role in improving the efficiency of perovskite solar cells. In-depth analysis of the results elucidates that the performance of both types of simulated structure is critically dependent on the crystallinity of the perovskite absorber layer. Furthermore, the performance of the lead-based structure is more dependent on the nature of the ETM/perovskite interface than that of the perovskite/HTM interface while the tin-based structure is dependent on the nature of both the interfaces. Moreover, the tin-based structure reveals a possibility of achieving performance comparable/superior to that of its lead-based counterpart by reducing the defect density inside the absorber layer. The findings are key towards the performance enhancement in perovskite solar cells and especially tin-based perovskite solar cells, which are deemed to be a potential replacement for lead-based perovskite solar cells.

Lead-based perovskite solar cells had reached a bottleneck and demonstrated significant power conversion efficiency (PCE) growth matching the performance of traditional polycrystalline silicon solar cells. Lead-containing perovskite solar cell technology is on the verge of commercialization and has huge potential to replace silicon solar cells, but despite the very promising future of these perovskite solar cells, the presence of water-soluble toxic lead content is a growing concern in the scientific community and a major bottleneck for their commercialization. The less toxic, tin-based perovskite solar cells are promising alternatives for lead-free perovskite solar cells. Like lead-based perovskite, the general chemical formula composition of tin-based perovskite is ASnX3, where A is a cation and X is an anion (halogen). It is evident that tin-based perovskites, being less-toxic with excellent photoelectric properties, show respectable performance. Recently, numerous studies reported on the fabrication of Sn-based perovskite solar cells. However, the stability of this novel lead-free alternative material remains a big concern. One of the many ways to stabilize these solar cells includes addition of dopants. In this context, this article summarizes the most important fabrication routes employing dopants that have shown excellent stability for tin-based perovskite photovoltaics and elaborates the prospects of lead-free, tin based stable perovskite photovoltaics.

Tin-based perovskite solar cells (PVSCs) have emerged as the most promising lead-free perovskite materials owing to their superior optoelectronic properties. However, the deficiency of accurate control of the tin-based perovskite crystallization process increases the possibility of unexpected perovskite film morphology and defects, resulting in inferior power conversion efficiency (PCE). Meanwhile, the poor environmental stability of tin-based perovskite films hinders its further development. In this work, a unique polymer [poly(ethylene-co-vinyl acetate) (EVA)] is introduced into anti-solvent during spin coating of formamidinium tin tri-iodide (FASnI3) precursor solution. The C═O groups contained in EVA have a powerful Lewis acid-base complexation with uncoordinated tin atoms in perovskite grains, which can greatly improve the grain size, optimize the grain orientation, and decrease the surface defects of FASnI3 films. This strategy offers an impressive PCE of 7.72% with favorable reproducibility. More importantly, the PVSC devices based on FASnI3-EVA absorbers have a self-encapsulation effect, which exhibits distinguished moisture and oxygen barrier property, thereby retaining 62.4% of the original efficiency value after aging for 48 h in the air with a humidity of 60%. Such a convenient strategy provides a new inspiration for the establishment of stable and high-performance tin-based PVSCs.

<p indent=0mm>Organic–inorganic hybrid perovskites have been a focus in the photovoltaic research field due to their remarkable advantages such as tunable direct bandgap, low exciton binding energy, high light harvesting, and so on. The power conversion efficiency (PCE) of lead (Pb)-based perovskite solar cells (PSCs) has been rapidly raised from 3.8% to 25.5% over the decades. With the advantages of a simple preparation process and low production cost, PSCs have great potential in commercialization. However, the toxicity of lead in traditional PSCs limits their large-scale production. Among all lead-free perovskites, the tin-based one inherits the majority of the excellent photoelectric properties of lead-based perovskites. However, the maximum PCE of tin-based PSCs has only exceeded 13%. Although the electronic structure of Sn²⁺ is similar to that of Pb²⁺, it is easy to be oxidized to Sn⁴⁺, and the formation energy of Sn vacancy defects is low, resulting in heavy p-doping in tin-based perovskite films. The background carrier concentrations of tin-based perovskites are as high as <sc>10¹⁸–10²⁰ cm^–3,</sc> which makes photo-generated carriers easy to be recombined. Tin-based perovskites usually experience single-molecule recombination, accompanied by a small amount of bi-molecular recombination, and Auger recombination is negligible. Therefore, reducing recombination in tin-based perovskites is to suppress the single-molecule recombination. At present, additive engineering and component modification strategies are mainly adopted to inhibit carrier recombination in tin-based PSCs. Additive engineering includes tin compensating additives, reducing additives and some other additives which interact with perovskites. Theories and experiments show that adding tin compensating additives in precursor solution can effectively improve the chemical potential of Sn and increase the formation energy of tin vacancies. Although the work mechanism of stannous halide as an additive is not fully understood, it has become an indispensable part to prepare high performance tin-based PSCs. The introduction of reducing additives in the precursor can effectively reduce Sn⁴⁺ and inhibit the oxidation of Sn²⁺, thereby inhibiting the generation of tin vacancies, optimizing the morphology of the film, and improving the efficiency and stability of the device. In addition, some additives which interact with perovskite through coordination bonds, ionic bonds and hydrogen bonds can optimize the nucleation rate of tin-based perovskites and passivate the unsaturated coordination of Sn²⁺ at the grain boundaries. The composition modification of tin-based perovskites mainly includes A-site and X-site substitutions. Since the band structure of tin-based perovskites is mainly determined by Sn and X ions, A-site cation substitution only fine-tunes the bandgap of the perovskite. However, A-site cation substitution can tune the tolerance factor of perovskite, thereby improving the efficiency and stability of perovskite. As the alkyl chain of the A-site cation gradually increases, low-dimensional perovskites will be formed. The low-dimensional perovskite can inhibit the self-doping and ion migration, improve the efficiency and stability of the PSCs. It is worth noting that the current efficient tin-based PSCs are mainly focused on low-dimensional perovskites. In addition, since the np² electrons of halogens directly participate in the construction of the electronic structure, the bandgap of tin-based perovskites can be directly changed by adjusting the X-site anions. Compared with lead-based perovskites, tin-based ones have more suitable bandgap and higher theoretical efficiency. At the same time, the low toxicity of tin-based perovskites is also conducive to their large-scale industrial production. It is believed that with the in-depth research, tin-based perovskite will surely exert its full potential in the photovoltaic field.

In this work, the effect of some parameters on tin-based perovskite (CH3NH3SnI3) solar cell were studied through device simulation with respect to adjusting the doping concentration of the perovskite absorption layer, its thickness and the electron affinities of the electron transport medium and hole transport medium, as well as the defect density of the perovskite absorption layer and hole mobility of hole transport material (HTM). A device simulator; the one-dimensional Solar Cells Capacitance Simulator (SCAPS‑1D) program was used for simulating the tin-based perovskite solar cells. The current-voltage (J-V) characteristic curve obtained by simulating the device without optimization shows output cell parameters which include; open circuit voltage (Voc) = 0.64V, short circuit current density (Isc) = 28.50mA/, fill factor (FF) = 61.10%, and power conversion efficiency (PCE) = 11.30% under AM1.5 simulated sunlight of 100mW/cm2 at 300K. After optimization, values of the doping concentration, defect density, electron affinity of electron transport material and hole transport material were determined to be: 1.0x1016cm-3, 1.0x1015cm-3, 3.7 eV and 2.3 eV respectively. Appreciable values of solar cell parameters were obtained with Jsc of 31.38 mA/cm2, Voc of 0.84 V, FF of 76.94% and PCE of 20.35%. when compared with the initial device without optimization, it shows improvement of ~1.10 times in Jsc, ~1.80 times in PCE, ~1.31 times in Voc and ~1.26 time in FF. The results show that the lead-free CH3NH3SnI3 perovskite solar cell which is environmentally friendly is a potential solar cell with high theoretical efficiency of 20.35%.

The Tin-based perovskite is an encouraging material in the development of non-toxic solar cell application, but its performance is limited by the poor chemical stability against oxygen and moisture. Therefore, tin-based perovskite solar cells are mostly fabricated in inverted planar device structures and the selection of underlying hole transport material plays a significant role in device stability. In this work, we report the comparison study between a metal oxide, nickel oxide, and polymeric poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT: PSS) as a hole transport layer on device efficiency and stability of tin-based PSC. We obtained comparatively higher power conversion efficiency (PCE) with NiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</inf> than others, however, the solar cell with PEDOT: PSS is more stable rather than NiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</inf> for the duration of 900 hrs in a nitrogen ambient, without encapsulation.

The power conversion efficiency of modern perovskite solar cells has surpassed that of commercial photovoltaic technology, showing great potential for commercial applications. However, the current high-performance perovskite solar cells all contain toxic lead elements, blocking their progress toward industrialization. Lead-free tin-based perovskite solar cells have attracted tremendous research interest, and more than 14% power conversion efficiency has been achieved. In tin-based perovskite, Sn2+ is easily oxidized to Sn4+ in air. During this process, two additional electrons are introduced to form a heavy p-type doping perovskite layer, necessitating the production of hole transport materials different from that of lead-based perovskite devices or organic solar cells. In this review, for the first time, we summarize the hole transport materials used in the development of tin-based perovskite solar cells, describe the impact of different hole transport materials on the performance of tin-based perovskite solar cell devices, and summarize the recent progress of hole transport materials. Lastly, the development direction of lead-free tin-based perovskite devices in terms of hole transport materials is discussed based on their current development status. This comprehensive review contributes to the development of efficient, stable, and environmentally friendly tin-based perovskite devices and provides guidance for the hole transport layer material design.