Synergetic Regulation of Interface Defects and Carriers Dynamics for High-Performance Lead-Free Perovskite Solar Cells

Vacuum-Evaporated Perovskite and Interfacial Modifier for Efficient Perovskite Solar Cells

Surface passivation of the perovskite layer is crucial for enhancing the photovoltaic performance of perovskite solar cells (PSCs). Vacuum evaporation is a scalable solvent-free method for depositing a uniform and homogenous thin layer with better control of film thickness. While the use of the vacuum-deposition method to obtain high-quality perovskite thin films is recently adapted, the evaporation of organic additives for surface passivation of the perovskite layer has not been widely studied. In this work, a vacuum evaporation method is introduced to uniformly deposit a novel multifunctional organic salt, 2-chlorophenethylamine pentafluorobenzene sulfonate (2-ClPEAPf), onto a perovskite surface. It is observed that 2-ClPEAPf not only effectively passivates the interfacial defects but also prevents moisture invasion into the perovskite film. As a result, planar n-i-p PSCs exhibit maximum PCE up to 25.16% with an aperture area of 0.1 cm2 and PCE of 24.00% (certified) on an active area of 1.0 cm2. In addition, the 0.1 cm2 device with vacuum-evaporated 2-ClPEAPf reveals enhanced operational stability maintaining 92.5% of its initial efficiency after 800 hours of continuous light irradiation.

Ameliorating Defects in Wide Bandgap Tin Perovskite Solar Cells Using Fluorinated Solvent and Hydrazide

Surface passivation with multifunctional molecules is an effective strategy to mitigate the defect and improve the performance and stability of perovskite solar cells (PSCs). Here, the fabrication of a wide bandgap-PSC is reported with tin perovskite (WB-Sn-HP; bandgap: 1.68 eV), followed by molecular surface passivation using 4-Fluoro-benzohydrazide (F-BHZ). WB-Sn-PSC has demonstrated a promising device efficiency of 11.14% with improved device stability. The key to enhancing device performance lies in the meticulous engineering of both surface and bulk properties of WB-Sn-HP film with F-BHZ treatment as a consequence of stronger electrostatic potential and molecular interaction with hydrazine and carbonyl functionalities. A compact perovskite film and highly crystalline film growth results in a longer carrier lifetime and surface defect mitigation with the control of Sn2+ oxidation as supported by theoretical calculations. This work underlines the promising potential of chemical engineering to improve the device performance of WB-Sn-PSC and stability using multifunctional passivating molecules.

Implementing Lattice and Energy Level Matching to Optimize Buried Interfaces for High-Performance Perovskite Solar Cells

In n-i-p type perovskite solar cells (PSCs), mismatches in energy level and lattice at the buried interface is highly detrimental to device performance. Here, thin PbS interconnect layer in situ coating on the SnO2 surface is grown. The function of PbS at the interface is different from the commonly used function of crystalline seeds in perovskite bulk. The theoretical calculation show that it helps construct an interconnect structure of SnO2/PbS/Perovskite with matched energy level and lattice. This not only increases conductivity of SnO2, but also upshifts Fermi energy levels (EF) of both SnO2 and buried perovskite due to charge transfer and perovskite's internal defect changes. Such a suitable energy level arrangement ensures a better energy level match at the interface, favoring efficient charge transfer and less open circuit voltage (Voc) loss. Additionally, in situ PL reveals that the template effect of PbS enable perovskite grain to grow bottom-up because of their highly matched lattice parameters. This growth mode optimizes buried interface contact and crystallinity of perovskite. Ultimately, after PbS modification, a remarkable power conversion efficiency (PCE) exceeding 24% and better device stability are obtained. This work demonstrates an effective interconnect layers strategy to realize ideal interface contact toward high-performance PSCs.

Internal Capsulation Via Self-Cross-linking and π-Effects Achieves Highly Stable Perovskite Solar Cells

Pursuing high stability becomes the core challenge in realizing the widespread application of perovskite solar cells (PerSCs). Here, a practical internal-capsulation strategy is proposed by introducing cross-linkable methacrylate analogs upon the perovskite layer, hindering ion migration and preventing lead leakage to achieve stable PerSCs. Butyl methacrylate (UMA) and benzyl methacrylate (BMA) can chemically interact with the perovskite layer, especially for the BMA dimer with significant π-interactions among the hanging benzene rings. Such configuration facilitated more compact coordination, thereby restoring the Fermi level of perovskite to a defect-free state and reducing carrier recombination losses. Moreover, by integrating the self-cross-linking and intermolecular π-effect, the application of BMA upgraded the internal capsulation from linear protection to a compact mesh-like scale. Consequently, the application of BMA not only boosted the efficiency to 25.31% but also greatly enhanced the stability of the perovskite layer, especially for water resistance and preventing lead linkage. The internal capsulation strategy upgrading from linear to mesh-like marked an innovative direction in protecting the perovskite layer, paving the way for more sustainable PerSCs in further application.

Synergistic Passivation on Buried Interface for Highly Efficient and Stable p-i-n Perovskite Solar Cells

The properties of an interface at the hole transport layer (HTL)/perovskite layer are crucial for the performance and stability of perovskite solar cells (PVSCs), especially the buried interface between HTL and perovskite layer. Here, a molecular named potassium 1-trifluoroboratomethylpiperidine (3FPIP) assistant-modified perovskite bottom interface strategy is proposed to improve the charge transfer capability and balances energy level between HTL and perovskite. BF3 - in the 3FPIP molecule interacts with undercoordinated Pb2+ to passivate iodine vacancies and enhance PVSCs performance. Furthermore, the infiltration of K+ ions into perovskite molecules enhances the crystallinity and stability of perovskite. Therefore, the PVSCs with the buried interface treatment exhibit a champion performance of 24.6%. More importantly, the corresponding devices represent outstanding ambient stability, remaining at 92% of the initial efficiency after 1200 h. This work provides a new method of buried interface engineering with functional group synergy.

Improving Hybrid Tin Halide Films of Lead-Free Perovskite Solar Cells with a Volatile Additive of Dipropyl Sulfide

Lead-free perovskite solar cells with hybrid tin halides (Sn-PVKs) as harvesters have attracted attention with respect to eliminating the contamination of conventional hybrid lead halides. However, Sn-PVK films usually have inferior performance due to rapid crystallization and uncontrollable morphology. Moreover, Sn2+ ions suffer from irreversible oxidation that results in self-doping and device instability. Additive engineering is a key strategy for improving the quality of Sn-PVK films, but solid residues of additives could degrade the transport-recombination process. In this work, dipropyl sulfide (DPS) was introduced as a volatile additive into the precursor solution, and no residue exists in the Sn-PVK films after thermal annealing. The coordinating ability of DPS molecules stabilized Sn2+ ions to form the intermediate complex, which retards the crystallization and oxidation of Sn-PVK films. Consequently, the power conversion efficiencies of devices increase from 11.0% to 12.9% with less recombination and a lower leakage current, and the stability of the devices is improved simultaneously.

Biomaterial Improves the Stability of Perovskite Solar Cells by Passivating Defects and Inhibiting Ion Migration

With the rapid improvement of power conversion efficiency (PCE), perovskite solar cells (PSCs) have broad application prospects and their industrialization will be the next step. Nevertheless, the performance and long-term stability of the devices are limited by the defect-induced nonradiative recombination centers and ions' migration inside the perovskite films. Here, usnic acid (UA), an easy-to-obtain and efficient natural biomaterial with a hydroxyl functional group (-OH) and four carbonyl groups (-C═O) was added to MAPbI3 perovskite precursor to regulate the crystallization process by slowing the crystallization rate, thereby expanding the crystal size and preparing perovskite films with low defect density. In addition, UA anchors the uncoordinated Pb2+ and suppresses the migration of I-ions, which enhances the stability of the perovskite film. Consequently, an impressive PCE exceeding 20% was achieved for inverted structure MAPbI3-based PSCs. More impressively, the optimized PSCs maintained 78% of the initial PCE under air with high humidity (RH ≈ 65%, 25-30 °C) for 1000 h. UA can be extracted from the plant, usnea, making it inexpensive and easy to obtain. Our work demonstrates the application of the plant material in PSCs and their industrialization, which is significant nowadays.

The impact of CBz-PAI interlayer in various HTL-based flexible perovskite solar cells: A drift-diffusion numerical study

In perovskite solar cells (PSCs), the charge carrier recombination obstacles mainly occur at the ETL/perovskite and HTL/perovskite interfaces, which play a decisive role in the solar cell performance. Therefore, this study aims to enhance the flexible PSC (FPSC) efficiency by adding the newly designed CBz-PAI-interlayer (simply CBz-PAI-IL) at the perovskite/HTL interface. In addition, substantial work has been carried out on five different HTLs (Se/Te-Cu2O, CuGaO2, V2O5, and CuSCN, including conventional Spiro-OMeTAD as a reference HTL with and without CBz-PAI-IL), using drift-diffusion simulation to find suitable FPSC design to attain the maximum PCE. Interestingly, PET/ITO/AZO/ZnO NWs/FACsPbBrI3/CBz-PAI/Se/Te-Cu2O/Au device architecture demonstrates the highest achievable power conversion efficiency (PCE) of 27.9 %. The findings of this study confirmed that the reference device (without IL) displays a large valence band edge (VBE)/highest occupied molecular orbital (HOMO) energy level misalignment compared to the modified interface device (with CBz-PAI-IL that reduces VBE/HOMO level mismatch) that eases the hole transport, simultaneously, it reduces the charge carrier recombinations at the interface, resulting in diminished Voc losses in the device. Furthermore, the influence of perovskite absorber thickness and defect density, parasitic resistances, and working temperature are systematically examined to govern the superior FPSC efficiency and concurrently understand the device physics.

Performance Enhancement of Tin-Based Perovskite Photodetectors through Bifunctional Cesium Fluoride Engineering

Tin halide perovskites are rising as promising candidates for next-generation optoelectronic materials due to their good optoelectronic properties and relatively low toxicity. However, the high defect density and the easy oxidation of Sn2+ have limited their optoelectronic performance. Herein, we report the treatment of the FASnI3 (formamidinium tin, FA) perovskite film by a bifunctional cesium fluoride (CsF) additive, which improves the film quality and significantly enhances the photoelectric performance. The responsivity of the perovskite-based photodetector (PD) with an optimal CsF concentration of 15% is over 60 times larger than that of the PD without CsF. It indicates that both the Cs substitution and the fluoride anion additive from CsF inhibit the oxidation of Sn2+, optimize the crystal growth, and passivate the defects, demonstrating the dual roles of the CsF additive in improving the photoelectric performance. This work offers valuable insights into the additive selection for developing high-quality tin-based perovskite films and devices.

Improved Air Stability for High-Performance FACsPbI3 Perovskite Solar Cells via Bonding Engineering

Despite the fact that perovskite solar cells (PSCs) are widely popular due to their superb power conversion efficiency (PCE), their further applications are still restricted by low stability and high-density defects. Especially, the weak binding and ion-electron properties of perovskite crystals make them susceptible to moisture attack under environmental stress. Herein, we report an overall sulfidation strategy via introduction of 1-pentanethiol (PT) into the perovskite film to inhibit bulk defects and stabilize Pb ions. It has been confirmed that the thiol groups in PT can stabilize uncoordinated Pb ions and passivate iodine vacancy defects by forming strong Pb-S bonds, thus reducing nonradiative recombination. Moreover, the favorable passivation process also optimizes the energy-level arrangement, induces better perovskite crystallization, and enhances the charge extraction in the full solar cells. Consequently, the PT-modified inverted device delivers a champion PCE of 22.46%, which is superior to that of the control device (20.21%). More importantly, the PT-modified device retains 91.5% of its initial PCE after storage in air for 1600 h and over 85% of its initial PCE after heating at 85 °C for 800 h. This work provides a new perspective to simultaneously improve the performance and stability of PSCs to satisfy their commercial applications.