Investigations aimed at producing 33% efficient perovskite–silicon tandem solar cells through device simulations

Elucidating Charge Carrier Dynamics in Perovskite-Based Tandem Solar Cells

Recently, multijunction tandem solar cells (TSCs) have presented high power conversion efficiency and revealed their immense potential in photovoltaic evolution. It is demonstrated that multiple light absorbers with various bandgap energies overcome the Shockley-Queisser limit of single-junction solar cells by absorbing the wide-range wavelength photons. Here, the main key challenges are reviewed, especially the charge carrier dynamics in perovskite-based 2-terminal (2-T) TSCs in terms of current matching, and how to manage these issues from a vantage point of characterization. To do this, the effect of recombination layers, optical and fabrication hurdles, and the impact of wide bandgap perovskite solar cells are discussed extensively. Afterward, this review focuses on various optoelectronics, spectroscopic, and theoretical (optical simulation) characterizations to figure out those issues, especially current-matching issues faced by the photovoltaic society. This review comprehensively provides deep insights into the relationship between the current-matching problems and the photovoltaic performance of TSCs through a variety of perspectives. Consequently, it is believed that this review is essential to address the main problems of 2-T TSCs, and the suggestions to elucidate the charge carrier dynamics and its characterization may pave the way to overcome such obstacles to further improve the development of 2-T TSCs in relation to the current-matching problems.

Exploring the potential of standalone and tandem solar cells with Sb2S3 and Sb2Se3 absorbers: a simulation study

Thin-film antimony chalcogenide binary compounds are potential candidates for efficient and low-cost photovoltaic absorbers. This study investigates the performance of Sb2S3 and Sb2Se3 as photovoltaic absorbers, aiming to optimize their efficiency. The standalone Sb2S3 and Sb2Se3 sub-cells are analyzed using SCAPS-1D simulations, and then a tandem structure with Sb2S3 as the top-cell absorber and Sb2Se3 as the bottom-cell absorber is designed, using the filtered spectrum and the current matching technique. The optimal configuration for maximum efficiency is achieved by adjusting the thickness of the absorber layer. The results show that antimony chalcogenide binary compounds have great potential as photovoltaic absorbers, enabling the development of efficient and low-cost solar cells. A remarkable conversion efficiency of 22.2% is achieved for the optimized tandem cell structure, with absorber thicknesses of 420 nm and 1020 nm for the top and bottom sub-cells respectively. This study presents a promising approach towards high-performance tandem solar cells.

Effects of the Electrical Properties of SnO2 and C60 on the Carrier Transport Characteristics of p-i-n-Structured Semitransparent Perovskite Solar Cells

Recently, metal halide perovskite-based top cells have shown significant potential for use in inexpensive and high-performance tandem solar cells. In state-of-the-art p-i-n perovskite/Si tandem devices, atomic-layer-deposited SnO2 has been widely used as a buffer layer in the top cells because it enables conformal, pinhole-free, and highly transparent buffer layer formation. In this work, the effects of various electrical properties of SnO2 and C60 layers on the carrier transport characteristics and the performance of the final devices were investigated using a numerical simulation method, which was established based on real experimental data to increase the validity of the model. It was found that the band alignment at the SnO2/C60 interface does, indeed, have a significant impact on the electron transport. In addition, as a general design rule, it was suggested that at first, the conduction band offset (CBO) between C60 and SnO2 should be chosen so as not to be too negative. However, even in a case in which this CBO condition is not met, we would still have the means to improve the electron transport characteristics by increasing the doping density of at least one of the two layers of C60 and/or SnO2, which would enhance the built-in potential across the perovskite layer and the electron extraction at the C60/SnO2 interface.

Dopant engineering for ZnO electron transport layer towards efficient perovskite solar cells

The conventional electron transport layer (ETL) TiO2 has been widely used in perovskite solar cells (PSCs), which have produced exceptional power conversion efficiencies (PCE), allowing the technology to be highly regarded and propitious. Nevertheless, the recent high demand for energy harvesters in wearable electronics, aerospace, and building integration has led to the need for flexible solar cells. However, the conventional TiO2 ETL layer is less preferred, where a crystallization process at a temperature as high as 450 °C is required, which degrades the plastic substrate. Zinc oxide nanorods (ZnO NRs) as a simple and low-cost fabrication material may fulfil the need as an ETL, but they still suffer from low PCE due to atomic defect vacancy. To delve into the issue, several dopants have been reviewed as an additive to passivate or substitute the Zn2+ vacancies, thus enhancing the charge transport mechanism. This work thereby unravels and provides a clear insight into dopant engineering in ZnO NRs ETL for PSC.

Lead-free, formamidinium germanium-antimony halide (FA4GeSbCl12) double perovskite solar cells: the effects of band offsets

Double halide perovskites have received massive attention due to their low toxicity, tunable bandgap, structural flexibility, and stability as compared to conventional 3D lead halide perovskites. Particularly, newly discovered formamidinium germanium-antimony halide (FA4GeSbCl12) double perovskites offer an excellent bandgap (∼1.3 eV) for solar cell (SC) applications. Therefore, in this study, for the first time, we have simulated FTO/TiO2/FA4GeSbCl12/Cu2O/Au planar SCs using SCAPS-1D, showing a maximum power conversion efficiency of 22.5% with Jsc = 34.52 mA cm-2, Voc = 0.76 V, and FF = 85.1%. The results show that the variation in valence and conduction band offsets (-0.4 to +0.2 eV and -0.4 to +0.57 eV) at the ETL/absorber and absorber/HTL interfaces dominate the SC performance. Also, different absorber defect densities (1 × 1014-1 × 1020 cm-3) and thicknesses (200-3000 nm) effectively influence the PCE. Moreover, simulated impedance spectroscopy (IS) data (through SCAPS-1D) were fitted using equivalent electrical circuits to extract relevant parameters, including Rs, RHF, and RLF, allowing us to better discuss the physics of the device. The fitted IS results strongly revealed that enhanced SC performance is associated with higher recombination resistance and a larger recombination lifetime. Likewise, a slight variation in the Rs (0 to 2.5 Ω cm2) highly impacts the PCE (22.5% to 19.7%). Furthermore, a tandem cell is designed by combining the top cell of ethylenediammonium-FASnI3 perovskite with the FA4GeSbCl12 bottom cell using a filtered spectrum strategy, which opens the door for multi-junction SC applications. These findings firmly reveal that the appropriate energy level alignment at interfaces with suitable material properties is the key to boosting SC performance.

Effect of BaTiO3 powder as an additive in perovskite films on solar cells

Perovskite solar cells (PSCs) are considered to be ideal energy devices, where perovskite-type organic metal halides act as light-absorbing materials. In PSCs, the photoexcitons are extracted and separated to afford high photoelectric conversion efficiency under the action of the built-in electric field (E bi). However, the current challenge is that a low E bi cannot provide a sufficient driving force to separate photonic excitons, which causes the captured charges to escape from the deep energy-level defect state. Here, the ferroelectric material barium titanate (BaTiO3) was directly introduced into the perovskite precursor solution to reduce the defection density (to 8.58 × 1017 cm-3) in PSCs and promote the separation of photoexcitons. Furthermore, the addition of BaTiO3 improved the quality of the perovskite film and significantly increased the photoelectric performance after the polarization treatment. This is mainly attributed to the residual polarization electric field generated by ferroelectric polarization, which increased the E bi of the PSCs and the width of the depletion layer and inhibited the non-radiative recombination of carriers. This work provides a possibility to design and develop optoelectronic devices with high-efficiency optoelectronic response behavior.