Prof Henry Snaith FRS

Abstract:

The fabrication of perovskite film is crucial for achieving efficient perovskite photoelectric device. Herein, a simple and novel encapsulation growth method was applied to prepare high-quality quasi-2D perovskite films with advantages of compact and uniform morphology, high crystallinity with lower defect density, enhanced photoluminescence quantum yield (PLQY) and optimized multidimensional domain distribution and crystallite orientation for perovskite light-emitting diodes (PeLEDs). The encapsulation growth method was found to decrease the proportion of the low-dimensional (n = 1,2,3) domains while increasing the high-dimensional domains content with randomly-oriented crystals, which simultaneously enhanced the overall energy landscape effect and charges transport within the quasi-2D perovskite films, and the PLQY of the quasi-2D perovskites significantly improved from 9.2% to 60.0%. Finally, an efficient flexible green PeLEDs was obtained with a high luminous efficiency (LE) of 47.1 cd/A, and a luminance brightness of 8300 cd/m , and an efficient sky-blue PeLEDs was also achieved with record EQE of 12.8% by using encapsulation growth method. This encapsulation growth method provides a promising strategy for boosting the efficiency of quasi-2D PeLEDs. 2

Abstract:

Although metal halide perovskite photovoltaics have shown an unprecedented rise in power conversion efficiency (PCE), they remain far from their theoretical PCE limit. Among the highest efficiencies to date are delivered when polycrystalline films are enhanced via “molecular passivation”, but this can introduce new instabilities, in particular under severe accelerated aging conditions (e.g., at 85 °C in the dark or under full spectrum simulated sunlight). Here, we utilize a benzylammonium bromide passivation treatment to improve device performance, achieving the champion stabilized power output (SPO) of 19.5 % in a p-i-n device architecture. We correlate the improved device performance with a significant increase in charge carrier diffusion lengths, mobilities, and lifetimes. Furthermore, treated devices maintain an increased performance during 120 h combined stressing under simulated full spectrum sunlight at 85 °C, indicating that enhancement from this passivation treatment is sustained under harsh accelerated aging conditions. This is a crucial step toward real-world operation-relevant passivation treatments.

Abstract:

Mixed tin‐lead halide perovskites are promising low‐bandgap absorbers for all‐perovskite tandem solar cells that offer higher efficiencies than single‐junction devices. A significant barrier to higher performance and stability is the ready oxidation of tin, commonly mitigated by various additives whose impact is still poorly understood for mixed tin‐lead perovskites. Here, the effects of the commonly used SnF2 additive are revealed for FA0.83Cs0.17SnxPb1−xI3 perovskites across the full compositional lead‐tin range and SnF2 percentages of 0.1–20% of precursor tin content. SnF2 addition causes a significant reduction in the background hole density associated with tin vacancies, yielding longer photoluminescence lifetimes, decreased energetic disorder, reduced Burstein–Moss shifts, and higher charge‐carrier mobilities. Such effects are optimized for SnF2 addition of 1%, while for 5% SnF2 and above, additional nonradiative recombination pathways begin to appear. It is further found that the addition of SnF2 reduces a tetragonal distortion in the perovskite structure deriving from the presence of tin vacancies that cause strain, particularly for high tin content. The optical phonon response associated with inorganic lattice vibrations is further explored, exhibiting a shift to higher frequency and significant broadening with increasing tin fraction, in accordance with lower effective atomic metal masses and shorter phonon lifetimes.