Hole Transport Layer-Free Low-Bandgap Perovskite Solar Cells for Efficient All-Perovskite Tandems

Low-bandgap (LBG, Eg  ≈1.25 eV) tin-lead (Sn-Pb) perovskite solar cells (PSCs) play critical roles in constructing efficient all-perovskite tandem solar cells (TSCs) that can surpass the efficiency limit of single-junction solar cells. However, the traditional poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) hole transport layer (HTL) in LBG PSCs usually restricts device efficiency and stability. Here, a strategy of employing 2-aminoethanesulfonic acid (i.e., taurine) as the interface bridge to fabricate efficient HTL-free LBG PSCs with improved optoelectronic properties of the perovskite absorbers at the buried contacts is reported. Taurine-modified ITO substrate has lower optical losses, better energy level alignment, and higher charge transfer capability than PEDOT:PSS HTL, leading to significantly improved open-circuit voltage (VOC ) and short-circuit current density of corresponding devices. The best-performing LBG PSC with a power conversion efficiency (PCE) of 22.50% and an impressive VOC of 0.911 V is realized, enabling all-perovskite TSCs with an efficiency of 26.03%. The taurine-based HTL-free TSCs have highly increased stability, retaining more than 90% and 80% of their initial PCEs after constant operation under 1-sun illumination for 600 h and under 55 °C thermal stress for 950 h, respectively. This work provides a facile strategy for fabricating efficient and stable perovskite devices with a simplified HTL-free architecture.

Mechanistic Understanding of Oxidation of Tin-based Perovskite Solar Cells and Mitigation Strategies

Tin (Sn)-based perovskites as the most promising absorber materials for lead-free perovskite solar cells (PSCs) have achieved the record efficiency of over 14 %. Although suppressing the oxidation of Sn-based perovskites is a frequently concerned topic for Sn-based PSCs, many studies have given vague explanations and the mechanisms are still under debate. This is in principal due to the lack of an in-depth understanding of various and complex intrinsic and extrinsic factors causing the oxidation process. In this context, we critically review the chemical mechanism of facile oxidation of Sn-based perovskites and differentiate its detrimental effects at material- and device-level. More importantly, we classify and introduce the intrinsic factors (raw materials and solvent of perovskite precursors) and extrinsic factors (exposure to neutral oxygen and superoxide) causing the oxidation with their corresponding anti-oxidation improvement methods. The presented comprehensive understanding and prospect of the oxidation provide insightful guidance for suppressing the oxidation in Sn-based PSCs "from the beginning to the end".

2D Perovskite Mn2+ -Doped Cs2 CdBr2 Cl2 Scintillator for Low-Dose High-Resolution X-ray Imaging

High-performance X-ray scintillators with low detection limits and high light yield are of great importance and are a challenge for low-dose X-ray imaging in medical diagnosis and industrial detection. In this work, the synthesis of a new 2D perovskite, Cs₂ CdBr₂ Cl₂ , via hydrothermal reaction is reported. By doping Mn²⁺ into the perovskite, a yellow emission located at 593 nm is obtained, and the photoluminescence quantum yield (PLQY) of Cs₂ CdBr₂ Cl₂ :5%Mn²⁺ perovskite reaches the highest value of 98.52%. The near-unity PLQY and negligible self-absorption of Cs₂ CdBr₂ Cl₂ :5%Mn²⁺ enable excellent X-ray scintillation performance with a high light yield of 64 950 photons MeV^-1 and low detection limit of 17.82 nGy_air s^-1 . Moreover, combining Cs₂ CdBr₂ Cl₂ :5%Mn²⁺ with poly(dimethylsiloxane) to fabricate a flexible scintillator screen achieves low-dose X-ray imaging with a high resolution of 12.3 line pairs (lp) mm^-1 . The results suggest that Cs₂ CdBr₂ Cl₂ :5%Mn²⁺ is a promising candidate for low-dose and high-resolution X-ray imaging. The study presents a new approach to designing high-performance scintillators through metal-ion doping.