Shahrir Razey Sahamir

Tin–lead (Sn–Pb) perovskite solar cells (PSCs) with band gaps around 1.4 eV have attracted significant interest due to their great potential for obtaining high power conversion efficiencies (PCEs) as their band gaps are near the optimum band gap value predicted by the Shockley–Queisser (SQ) limit for single-junction solar cells. Methylammonium (MA)-free Sn–Pb PSCs are of particular interest due to their better intrinsic thermal stability relative to MA-based counterparts. However, the facile oxidation of Sn2+ to Sn4+ results in defect formation and nonradiative recombination, ultimately leading to poor photovoltaic performance. Herein, we report a hydrazine-based additive, phenethylhydrazine hydrochloride (PEHHCl), for enhancing the photovoltaic performance of MA-free Sn–Pb PSCs possessing a band gap of 1.41 eV. The hydrazine functionality of the PEHHCl effectively suppresses Sn2+ oxidation while simultaneously passivating grain boundary defects by coordinating with undercoordinated Sn and Pb sites, thus resulting in improved crystallinity, lower energetic disorder, optimized energy-level alignment, and reduced trap densities. Consequently, the PEHHCl-incorporated perovskite films demonstrated reduced trap-assisted nonradiative recombination, faster charge-carrier transport time, longer charge-carrier recombination times, longer charge-carrier diffusion lengths, and higher recombination resistance. As a result of these improvements, the PEHHCl-incorporated MA-free PSC demonstrated a champion PCE of 19.59% with a stabilized PCE of 19.55%, placing it among some of the high-performing MA-free Sn–Pb PSCs reported for the band gap range of around 1.4 eV.

SnF2 is widely used as an additive to suppress Sn2+ oxidation in tin perovskite solar cells (Sn-PVK-PVs). However, its effect differed between the two processing routes examined here. In this study, we evaluated the influence of SnF2 addition on dimethyl sulfoxide (DMSO)-free N,N-dimethylformamide (DMF):2-(methylamino)pyridine (2MAP)-based FASnI3 films in terms of optical properties, Sn oxidation state, crystal growth, charge transport, and device performance, and compared the results with those for conventional DMF:DMSO-based films. In the DMF:DMSO system, SnF2 addition improved the Urbach tail, suppressed the photoluminescence (PL) peak blueshift, prolonged the time-resolved PL (TRPL) lifetime, and increased the Sn2+ fraction in X-ray photoelectron spectroscopy (XPS) depth profiling. Thus, in DMSO-containing processes, SnF2 acts as an effective redox-stabilizing additive that suppresses Sn2+ oxidation. In contrast, in the DMF:2MAP system, the interior of the SnF2-free film was already Sn2+-rich, and the additional oxidation-suppression effect of SnF2 was limited. SnF2 addition was accompanied by reduced grain size, increased grain-boundary density, and higher dark current, together with lower short-circuit current density (Jsc), fill factor (FF), device performance, and initial operational output. These results demonstrate that the beneficial role of SnF2 is not universal and can be limited under the specific DMSO-free DMF:2MAP processing conditions employed here.

Tin-lead (Sn-Pb) perovskite solar cells are promising for tandem applications but face challenges with Sn²⁺ oxidation and defect-induced recombination, particularly with conventional hole transport layers (HTLs). We introduce ethylenediamine tetramethylphosphonic acid (EDTMP) as a novel interfacial modifier for Sn-Pb PSCs. EDTMP offers dual passivation capabilities through phosphonic acid anchoring to FTO and diamine interaction with perovskite defects. This strategy significantly reduces nonradiative recombination, extends carrier lifetimes, and improves film quality. Devices incorporating EDTMP achieved a remarkable power conversion efficiency exceeding 22% and excellent operational stability. Our findings provide a pathway toward simplified, scalable, and stable high-efficiency perovskite photovoltaics.

Due to the band offset, there is significant interfacial recombination between the tin-based perovskite and C₆₀, which exhibits excellent electron transport capability. Here, we introduce a novel strategy leveraging surface self-passivation through controlled thermal decomposition to reduce the level of interfacial recombination substantially. By carefully tuning the annealing temperature (70 vs 100 °C) and organic cation composition (diethylammonium (DEA) vs methylamine (MA)), we achieve selective surface restructuring and SnI₂ formation, effectively suppressing interfacial recombination at the perovskite/C₆₀ interface. Detailed characterization using scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and time-of-flight secondary ion mass spectrometry (ToF-SIMS) confirmed the formation of a stable SnI₂ passivation layer. At the same time, photoluminescence and quasi-Fermi level splitting (QFLS) analyses revealed a notable reduction in the interfacial recombination losses. Consequently, this surface self-passivation strategy significantly improved the power conversion efficiency (PCE) by approximately 1%, primarily through an open-circuit voltage (V_OC) increase of around 50 mV. Our findings underscore the critical role of interface engineering and thermal control in advancing the efficiency of Sn-based perovskite solar cells.

All‐perovskite tandem solar cells are regarded as the next generation of devices capable of enhancing the solar energy utilization rate. Unlike single‐junction perovskite solar cells (PSCs), the efficacy of tandem cells is contingent upon the performance of both the top and bottom cells. In this study, we employed a simultaneous co‐modification strategy to incorporate phenylethylammonium iodide (PEAI) at both the top and bottom interfaces of the perovskite film, aiming to boost the top cell's performance. Both experimental and theoretical findings indicate that PEAI not only elevates the perovskite film quality through chemical interactions but also mitigates nonradiative recombination within the device. Consequently, the efficiency of the wide‐bandgap (1.77 eV) PSCs based on nickel oxide (NiO_x) attained a level of 16.5%. Simultaneously, the all‐perovskite tandem solar cells achieved an efficiency of 26.81% and demonstrated superior stability.

Further improvement of the performance and stability of inverted perovskite solar cells (PSCs) is necessary for commercialization. Here, ferrocene derivative dibenzoylferrocene (DBzFe) is used as an additive to enhance the performance and stability of MA‐ and Br‐ free PSCs. The results show that the introduction of DBzFe not only passivates the defects in the film but also inhibits the ion migration in the film. The final device achieves a power conversion efficiency (PCE) of 23.53%, which is one of the highest efficiencies currently based on self‐assembled monolayers (SAMs). Moreover, it maintains more than 96.4% of the original efficiency when running continuously for 400 h at the maximum power point.