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The contributions of photon recycling and light scattering to the performance of perovskite solar cells are quantified.

phase stabilizing, [8] charge carrier management, [9] pseudo-halide anion engineering, [10] and intact 2D/3D perovskite bilayer employment; [5] up to 25.5% certificated PCE of the device has been reported.Most of the previous investigations were focused on inner device factors such as materials and junctions of the PSC. [11][12][13][14][15][16][17] However, gathering entire light wavelength (350-850 nm) and putting it into the PSC are equally important to enhancing the PCE by controlling the mechanism inside the PSC. Once a sticker-type anti-reflective (AR) film is simply attached to the device, it effectively increases light transition efficiency (LTE, defined as the amount of external light transmitted to the device) independently of the development of inner device technology. On account of efficient transference of external sunlight into the PSC with the aid of AR film, the external quantum efficiency (EQE) of PSC increases across the entire wavelength which means increase of short-circuit current density (J sc ). [18,19] Therefore, the application of proper sticker-type AR film to PSCs is the most effective and easiest approach to increasing the PCE of the photovoltaic devices. [20,21] Such a sticker-type AR film has been continuously developed with the progress of PSC, with the help of its high LTE and easy applicability on transparent substrates. [22][23][24][25] To obtain high LTE for PSC, the highest priority for AR film is to reduce reflection of incident light by effectively reducing the difference in refractive index (n) that occurs at the substrate interface, because the reflection is caused by the sudden change of refractive index at the interface between the air and substrate. Therefore, it is necessary to use a material with low refractive index for AR film. In addition, forming nanostructures on surface of the AR film can enhance the AR effect based on the structural gradient change of the refractive index from air to substrate. [26][27][28][29] Furthermore, in order to expand and commercialize the gradually developing PSC technology, advanced AR film that can be easily applied to flexible and lightweight PSC (that is important for the wearable and portable electronic devices) is needed. For this reason, a sticker-type ultra-thin AR film is essential. The thinner the AR film attached to the flexible PSC, the better the mechanical stability of the device due to the reduction of the applied stress on the perovskite layer. [30] However, the commercial AR film is developed by biasing toward Sticker-type anti-reflective (AR) film is a powerful route to achieve the highest efficiency and commercialization of perovskite solar cells (PSCs) by improving the light transition efficiency (LTE). However, conventionally used AR film has high flexural rigidity owing to its limitation of material and thickness, thereby hindering its application to high-efficiency flexible devices. This paper proposes a sticker-type ultra-thin perfluoropolyether (PFPE) AR film (SUPA) made of PFPE (n = 1.34) that is fabricated thro...

Fast diffusion of charge carriers is crucial for efficient charge collection within their lifetime in perovskite solar cells. While lateral transient photoluminescence microscopies have been popularly used to characterise charge diffusion in perovskites, there exists a discrepancy between low diffusion coefficients measured to be on the order of 10 -2 cm 2 s -1 and near-unity charge collection efficiencies achieved in practical solar cells. Here, we reveal hidden microscopic dynamics in halide perovskites through four-dimensional (4D -x, y, z, t) tracking of charge carriers. First, we investigate a method for characterising out-of-plane diffusion of charge carriers applicable to general semiconductors by exploiting the effect of optical self-filtering on external photoluminescence spectra. By combining this approach with confocal microscopy, we discover a strong local heterogeneity of vertical charge diffusivities varying from 0.006 to 0.3 cm 2 s -1 in a 3D perovskite film, arising from the difference between intragrain and intergrain diffusion. By contrast, conventional in-plane measurements yield a diffusivity of only 0.02 cm 2 s -1 in the same film, which is limited by intergrain charge transport. In the out-of-plane direction across the film thickness, our 4D tracking visualises that most charge carriers are efficiently transported through the direct intragrain pathways or via indirect detours through nearby areas with a fast diffusion. Finally, our technique also quantifies significant anisotropy of exciton diffusion in a vertically stacked 2D perovskite film. The observed anisotropy and heterogeneity of charge carrier diffusion in perovskites rationalize their high performance shown in real devices. Our work also foresees that further control of polycrystal growth will enable solar cells with micrometres-thick perovskites to achieve both long optical path length and efficient charge collection simultaneously.

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