Weiyan Wang

The performance of wide‐bandgap (WBG) perovskite sub‐cells in tandem solar cells is largely constrained by grain boundary and surface defects, along with unfavorable interfacial energy level alignment. To address these issues, we propose a bilayer co‐ligand post‐treatment strategy, initially employing 3‐(methylthio)propylamine hydroiodide (3MTPAI) and 1, 3‐propanediamine dihydroiodide (PDAI ₂ ), followed by a secondary piperazinium iodide (PI) layer. In this design, 3MTPAI penetrates the grain boundaries to passivate both grain boundary and surface defects, thereby suppressing non‐radiative recombination, while PDAI ₂ forms an initial surface dipole layer to enhance the built‐in electric field. The subsequent PI layer not only passivates residual defects but also generates a second dipole layer that acts synergistically with the first, facilitating carrier transport at the interface. Consequently, the optimized WBG (1.68 eV) single‐junction and tandem devices achieve power conversion efficiencies (PCEs) of 23.55% and 32.33%, respectively, and show no efficiency loss after 500 h of operation. This work demonstrates that the bilayer co‐ligand strategy offers valuable insights for developing efficient and stable single‐junction and tandem solar cells.

Atomic layer deposition (ALD) of compact tin oxide (SnO ₂ ) sputtering buffer layer plays a crucial role in high‐performance semitransparent perovskite solar cells (ST‐PSCs) and perovskite/silicon tandem solar cells. However, when the substrate exhibits low reactivity with the ALD reactants, the ALD process tends to follow an island growth mode, leading to a prolonged incubation period and pinhole films, which ultimately degrade device performance. In this study, the substrate is activated by simply altering precursor introduced sequence, switching from introducing the tin precursor first to introducing the oxygen precursor first. The hydroxyl groups generated by the oxygen precursor enhance nucleation sites on the substrate, allowing the initial ALD films growth transforming from island‐like mode to layer‐by‐layer mode, resulting in dense and vertically uniform SnO ₂ films. Semitransparent PSCs constructed with dense ALD SnO ₂ layer effectively mitigate sputtering‐induced damage and improve the interface properties. As a result, the initial power conversion efficiency (PCE) of the ST‐PSC increased from 19.37% to 19.99%, corresponding to the improvement by 3.2%. The perovskite/silicon tandem solar cells are also fabricated with PCE of 28.77%. Furthermore, ST‐PSCs with dense ALD SnO ₂ layer exhibit improved moisture and thermal stability, which maintain 96.6% and 95.6% of initial PCE after being stored at relative humidity of 30% for 600 h and 85 °C for 600 h, respectively. This study provides a simple and effective approach for fabricating dense and uniform ALD SnO ₂ buffer layers, demonstrating their potential application not only in efficient semitransparent perovskite solar cells and tandem solar cells but also in other optoelectrical devices.

Indium tin oxide (ITO) films are widely used as transparent electrodes in perovskite solar cells (PSCs). However, the limited supply and high cost of rare indium pose challenges to the sustainable development of PSCs. In this study, sputtered tantalum‐doped tin oxide (TTO) films with post‐annealing in H ₂ (TTO‐H ₂ ), are proposed as an attractive alternative to ITO electrodes in PSCs. It is demonstrated that TTO films post‐annealed in H ₂ atmosphere exhibited lower sheet resistance of 91.8 Ω sq ⁻¹ , with a higher carrier concentration of 6.51 × 10 ²⁰ cm ⁻³ , and a higher mobility of 6.96 cm ² V ⁻¹ s ⁻¹ , compared to TTO films post‐annealed in O ₂ and N ₂ atmospheres. The mechanism behind the improvement in electrical characteristics is revealed. Indium‐free inverted PSCs using TTO‐H ₂ bottom electrodes are constructed. High‐quality TTO‐H ₂ /MeO‐2PACZ/perovskite interface is demonstrated with advantages of higher built‐in electric field, lower defect state density, and improved carrier transport ability, compared to the reference ITO/MeO‐2PACZ/perovskite interface. Thus, the prepared PSCs using TTO‐H ₂ electrodes exhibit improved photovoltaic performance compared to reference ITO‐based PSCs: the open‐circuit voltage ( V _oc ) is enhanced from 1.100 to 1.134 V; and the power conversion efficiency (PCE) is enhanced from 20.58% to 20.77% with 1% increase. This study demonstrates the indium‐free PSCs with enhanced V _oc and PCE for the first time, and elucidates the underlying mechanisms, providing new insights for high‐performance and low‐cost PSCs.

Foldable perovskite solar cells (PSCs) have promising applications in self‐powered wearable and portable electronic devices. However, the folding stability requires further improvement through mitigating the strain in brittle layers under folding deformation. Herein, sandwich‐structured PSCs (SS‐PSCs) are constructed by coating a protection layer at the back of the device, to tune the neutral plane (NP) place into the brittle perovskite films. To accurately regulating the NP place, the effect of protective layer thickness on the strain distribution in PSCs is simulated. The SS‐PSCs are experimentally prepared using Al₂O₃/polyethylene terephthalate (PET) protection layer with optimum thickness, combined with ultrathin silver foldable electrodes. Benefitting from the water‐resisting Al₂O₃/PET, the SS‐PSCs demonstrate high environment stability which maintains 85.1% of original efficiency after 700 h in humidity of 50% ± 10%. More importantly, the SS‐PSCs exhibit excellent mechanical stability, which maintains >90% of the initial efficiency after bending with 4000 cycles at radius of 0.2 mm, and even 67.2% of the initial efficiency after 50 direct folding cycles. As far as it is known, it is one of the best mechanical stable devices. The findings pave the way for realizing not only foldable PSCs but also other foldable optoelectronic devices, such as sensors and organic light emitting devices.

Perovskite solar cell (PSC) using ultrathin metal transparent electrode is a promising power source for wearable electronics and aerospace applications. However, the environmental stability of device is challenging, due to the undesirable interdiffusion of metal and halogen ions. In this work, PSCs are constructed by using ultrathin copper (Cu) electrodes with low reactivity, combined with potassium methacrylate (KMMA) additive. On one hand, carbonyl groups in KMMA interact with the perovskite and improve quality of perovskite films. As a result, the power conversion efficiency (PCE) of ultrathin Cu‐based PSC is increased from 12.49% to 14.72%. On the other hand, benefitting from the binding of K⁺ with halogen ion, the interdiffusion of Cu and I ions is hindered. Thus, PSCs retain 80% and 75% of the initial PCE under heating at 85 °C for 130 h and maximum power point for 300 h, respectively. To the best of the knowledge, it is one of the best thermal and operational stability for the PSCs using metal‐based electrodes. At last, the symmetric PSCs exhibit superior folding stability which maintain 85.3% of initial PCE after folding for 500 cycles. Foldable PSCs on ultrathin Cu electrodes with excellent stability are attractive power sources in wearable applications.