Ionic Liquid Modified Polymer Intermediate Layer for Improved Charge Extraction toward Efficient and Stable Perovskite/Silicon Tandem Solar Cells.

Monolithic perovskite/silicon tandem solar cells have been attracted much attention in recent years. Despite their high performances, the stability issue of perovskite-based devices is recognized as one of the key challenges to realize industrial application. When comes to the perovskite top subcell, the interface between perovskite and electron transporting layers (usually C60) significantly affects the device efficiency as well as the stability due to their poor adhesion. Here, different from the conventional interfacial passivation using metal fluorides, a hybrid intermediate layer is proposed-PMMA functionalized with ionic liquid (IL)-is introduced at the perovskite/C60 interface. The application of PMMA essentially improves the interfacial stability due to its strong hydrophobicity, while adding IL relieves the charge accumulation between PMMA and the perovskite. Thus, an optimal wide-bandgap perovskite solar cells achieves power conversion efficiency of 20.62%. These cells are further integrated as top subcells with silicon bottom cells in a monolithic tandem structure, presenting an optimized PCE up to 27.51%. More importantly, such monolithic perovskite/silicon cells exhibit superior stability by maintaining 90% of initial efficiency after 1200 h under continuous illumination.

π-π Stacking at the Perovskite/C60 Interface Enables High-Efficiency Wide-Bandgap Perovskite Solar Cells.

Interface passivation is a key method for improving the efficiency of perovskite solar cells, and 2D/3D perovskite heterojunction is the mainstream passivation strategy. However, the passivation layer also produces a new interface between 2D perovskite and fullerene (C60), and the properties of this interface have received little attention before. Here, the underlying properties of the 2D perovskite/C60 interface by taking the 2D TEA2PbX4 (TEA = C6H10NS; X = I, Br, Cl) passivator as an example are systematically expounded. It is found that the 2D perovskite preferentially exhibits (002) orientation with the outermost surface featuring an oriented arrangement of TEACl, where the thiophene groups face outward. The outward thiophene groups further form a strong π-π stacking system with C60 molecule, strengthening the interaction force with C60 and facilitating the creation of a superior interface. Based on the vacuum-assisted blade coating, wide-bandgap (WBG, 1.77 eV) perovskite solar cells achieved impressive records of 19.28% (0.09 cm2) and 18.08% (1.0 cm2) inefficiency, respectively. This research not only provides a new understanding of interface processing for future perovskite solar cells but also lays a solid foundation for realizing efficient large-area devices.

Organizing Uniform Phase Distribution in Methylammonium-Free 1.77 eV Wide-Bandgap Inverted Perovskite Solar Cells.

Disordered crystallization and poor phase stability of mixed halide perovskite films are still the main factors that compromise the performance of inverted wide bandgap (WBG; 1.77 eV) perovskite solar cells (PSCs). Great difficulties are evidenced due to the very different crystallization rates between I- and Br-based perovskite components through DMSO-alone assisted anti-solvent process. Here, a zwitterionic additive strategy is reported for finely regulating the crystal growth of Cs0.2 FA0.8 Pb(I0.6 Br0.4 )3 , thereby obtaining high-performance PSCs. The aminoethanesulfonic acid (AESA) is introduced to form hydrogen bonds and strong PbO bonds with perovskite precursors, realizing the complete coordination with both the organic (FAI) and inorganic (CsI, PbI2 , PbBr2 ) components, balancing their complexation effects, and realizing AESA-guided fast nucleation and retarded crystallization processes. This treatment substantially promotes homogeneous crystal growth of I- and Br-based perovskite components. Besides, this uniformly distributed AESA passivates the defects and inhibits the photo-induced halide segregation effectively. This strategy generates a record efficiency of 19.66%, with a Voc of 1.25 V and FF of 83.7% for an MA-free WBG p-i-n device at 1.77 eV. The unencapsulated devices display impressive humidity stability at 30 ± 5% RH for 1000 h and much improved continuous operation stability at MPP for 300 h.

Passivation of Sodium Benzenesulfonate at the Buried Interface of a High-Performance Wide-Bandgap Perovskite Solar Cell.

The phase segregation of wide-bandgap perovskite is detrimental to a device's performance. We find that Sodium Benzenesulfonate (SBS) can improve the interface passivation of PTAA, thus addressing the poor wettability issue of poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine](PTAA). This improvement helps mitigate interface defects caused by poor contact between the perovskite and PTAA, reducing non-radiative recombination. Additionally, enhanced interface contact improves the crystallinity of the perovskite, leading to higher-quality perovskite films. By synergistically controlling the crystallization and trap passivation to reduce the phase segregation, SBS-modified perovskite solar cells (PSCs) achieved a power conversion efficiency (PCE) of 20.27%, with an open-circuit voltage (Voc) of 1.18 V, short-circuit current density (Jsc) of 20.93 mA cm-2, and fill factor (FF) of 82.31%.

Reducing Perovskite/C60 Interface Losses via Sequential Interface Engineering for Efficient Perovskite/Silicon Tandem Solar Cell.

Wide-bandgap (WBG) perovskite solar cells hold tremendous potential for realizing efficient tandem solar cells. However, nonradiative recombination and carrier transport losses occurring at the perovskite/electron-selective contact (e.g. C60 ) interface present significant obstacles in approaching their theoretical efficiency limit. To address this, a sequential interface engineering (SIE) strategy that involves the deposition of ethylenediamine diiodide (EDAI2 ) followed by sequential deposition of 4-Fluoro-Phenethylammonium chloride (4F-PEACl) is implemented. The SIE technique synergistically narrows the conduction band offset and reduces recombination velocity at the perovskite/C60 interface. The best-performing WBG perovskite solar cell (1.67 eV) delivers a power conversion efficiency (PCE) of 21.8% and an impressive open-circuit voltage of 1.262 V. Moreover, through integration with double-textured silicon featuring submicrometer pyramid structures, a stabilized PCE of 29.6% is attained for a 1 cm2 monolithic perovskite/silicon tandem cell (certified PCE of 29.0%).

Efficient Semi-Transparent Wide-Bandgap Perovskite Solar Cells Enabled by Pure-Chloride 2D-Perovskite Passivation.

Wide-bandgap (WBG) perovskite solar cells suffer from severe non-radiative recombination and exhibit relatively large open-circuit voltage (VOC) deficits, limiting their photovoltaic performance. Here, we address these issues by in-situ forming a well-defined 2D perovskite (PMA)2PbCl4 (phenmethylammonium is referred to as PMA) passivation layer on top of the WBG active layer. The 2D layer with highly pure dimensionality and halide components is realized by intentionally tailoring the side-chain substituent at the aryl ring of the post-treatment reagent. First-principle calculation and single-crystal X-ray diffraction results reveal that weak intermolecular interactions between bulky PMA cations and relatively low cation-halide hydrogen bonding strength are crucial in forming the well-defined 2D phase. The (PMA)2PbCl4 forms improved type-I energy level alignment with the WBG perovskite, reducing the electron recombination at the perovskite/hole-transport-layer interface. Applying this strategy in fabricating semi-transparent WBG perovskite solar cells (indium tin oxide as the back electrode), the VOC deficits can be reduced to 0.49 V, comparable with the reported state-of-the-art WBG perovskite solar cells using metal electrodes. Consequently, we obtain hysteresis-free 18.60%-efficient WBG perovskite solar cells with a high VOC of 1.23 V.

Efficiency Enhancement of Wide Bandgap Lead Perovskite Solar Cells with PTAA Surface-Passivated with Monomolecular Layer from the Viewpoint of PTAA Band Bending.

This report is on the efficiency enhancement of wide bandgap lead halide perovskite solar cells (WBG Pb-PVK PSCs) consisting of FA0.8Cs0.2PbI1.8Br1.2 as the light-harvesting layer. WGB Pb-PVK PSCs have attracted attention as the top layer of all perovskite-tandem solar cells. Poly[bis(4-phenyl) (2,4,6-trimethylphenyl) amine] (PTAA), a conductive polymer, is always used as the hole transporting layer (HTL) for Pb-PVK PSCs. Nevertheless, the hydrophobic surface of the PTAA sometimes destroys the growth of the FA0.8Cs0.2PbI1.8Br1.2 film. On the other hand, the Fermi level of PTAA is not well matched with that of perovskite film. Thus, the PCE of the WBG Pb-based PSCs with PTAA as the HTL was not very high. In this report, the efficiency of the FA0.8Cs0.2PbI1.8Br1.2 is improved by passivating the surface of the PTAA with a monomolecular layer, where the surface becomes hydrophilic, and the band bending of the PTAA layer is improved to cause swift hole collection. Finally, WBG Pb-PVK PSCs (1.77 eV) with 16.52% efficiency are reported.

Optimizing Crystallization in Wide-Bandgap Mixed Halide Perovskites for High-Efficiency Solar Cells.

Wide-bandgap (WBG) perovskites have attracted considerable attention due to their adjustable bandgap properties, making them ideal candidates for top subcells in tandem solar cells (TSCs). However, WBG perovskites often face challenges such as inhomogeneous crystallization and severe nonradiative recombination loss, leading to high open-circuit voltage (VOC ) deficits and poor stability. To address these issues, a multifunctional phenylethylammonium acetate (PEAAc) additive that enhances uniform halide phase distribution and reduces defect density in perovskite films by regulating the mixed-halide crystallization rate, is introduced. This approach successfully develops efficient WBG perovskite solar cells (PSCs) with reduced VOC loss and enhanced stability. By applying this universal strategy to the FAMACsPb(I1- x Brx )3 system with a range of bandgaps of 1.73, 1.79, 1.85, and 1.92 eV, power conversion efficiencies (PCE) of 21.3%, 19.5%, 18.1%, and 16.2%, respectively, are attained. These results represent some of the highest PCEs reported for the corresponding bandgaps. Furthermore, integrating WBG perovskite with organic photovoltaics, an impressive PCE of over 24% for two-terminal perovskite/organic TSCs, with a record VOC of ≈ 2.2 V is achieved. This work establishes a foundation for addressing phase separation and inhomogeneous crystallization in Br-rich perovskite components, paving the way for the development of high-performance WBG PSCs and TSCs.

Steric Engineering Enables Efficient and Photostable Wide-Bandgap Perovskites for All-Perovskite Tandem Solar Cells.

Wide-bandgap (WBG, ≈1.8 eV) perovskite is a crucial component to pair with narrow-bandgap perovskite in low-cost monolithic all-perovskite tandem solar cells. However, the stability and efficiency of WBG perovskite solar cells (PSCs) are constrained by the light-induced halide segregation and by the large photovoltage deficit. Here, a steric engineering to obtain high-quality and photostable WBG perovskites (≈1.8 eV) suitable for all-perovskite tandems is reported. By alloying dimethylammonium and chloride into the mixed-cation mixed-halide perovskites, wide bandgaps are obtained with much lower bromide contents while the lattice strain and trap densities are simultaneously minimized. The WBG PSCs exhibit considerably improved performance and photostability, retaining >90% of their initial efficiencies after 1000 h of operation at maximum power point. With the triple-cation/triple-halide WBG perovskites enabled by steric engineering, a stabilized power conversion efficiency of 26.0% in all-perovskite tandem solar cells is further obtained. The strategy provides an avenue to fabricate efficient and stable WBG subcells for multijunction photovoltaic devices.

Constructing Monolithic Perovskite/Organic Tandem Solar Cell with Efficiency of 22.0% via Reduced Open-Circuit Voltage Loss and Broadened Absorption Spectra.

Combining the high stability under UV light of the wide bandgap (WBG) perovskite solar cells (pero-SCs) and the broad near-infrared absorption spectra of the narrow bandgap (NBG) organic solar cells (OSCs), the perovskite/organic tandem solar cells (TSCs) with the WBG pero-SC as front cell and the NBG OSC as rear cell have attracted attention . However, the photovoltaic performance of the perovskite/organic TSCs needs to be further improved. Herein, nonradiative charge recombination loss is reduced through bulk defect passivation in the WBG pero-SC front subcell and broadening the range of absorption spectra of the NBG OSC rear cell. For the WBG pero-SCs, an organic cation chloro-formamidinium is introduced into FA0.6 MA0.4 Pb(I0.6 Br0.4 )3 to passivate the bulk defects in the perovskite film and the WBG pero-SC displays high open-circuit voltage of 1.25 V and high fill factor of 83.0%. For the NBG OSCs, a new infrared-absorbing organic small molecule acceptor BTPV-4Cl-eC9 is designed and synthesized. Then, a monolithic perovskite/organic TSC is fabricated with the WBG pero-SC as the front cell and the NBG OSC as the rear cell, and the TSC demonstrates high power conversion efficiency up to 22.0%. The results indicate that the perovskite/organic TSC is promising for future commercialization.