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Metal halide perovskite solar cells (PSCs) are an emerging photovoltaic technology with the potential to disrupt the mature silicon solar cell market. Great improvements in device performance over the past few years, thanks to the development of fabrication protocols.sup.1-3, chemical compositions.sup.4,5 and phase stabilization methods.sup.6-10, have made PSCs one of the most efficient and low-cost solution-processable photovoltaic technologies. However, the light-harvesting performance of these devices is still limited by excessive charge carrier recombination. Despite much effort, the performance of the best-performing PSCs is capped by relatively low fill factors and high open-circuit voltage deficits (the radiative open-circuit voltage limit minus the high open-circuit voltage).sup.11. Improvements in charge carrier management, which is closely tied to the fill factor and the open-circuit voltage, thus provide a path towards increasing the device performance of PSCs, and reaching their theoretical efficiency limit.sup.12. Here we report a holistic approach to improving the performance of PSCs through enhanced charge carrier management. First, we develop an electron transport layer with an ideal film coverage, thickness and composition by tuning the chemical bath deposition of tin dioxide (SnO.sub.2). Second, we decouple the passivation strategy between the bulk and the interface, leading to improved properties, while minimizing the bandgap penalty. In forward bias, our devices exhibit an electroluminescence external quantum efficiency of up to 17.2 per cent and an electroluminescence energy conversion efficiency of up to 21.6 per cent. As solar cells, they achieve a certified power conversion efficiency of 25.2 per cent, corresponding to 80.5 per cent of the thermodynamic limit of its bandgap. An improved device design for perovskite-based photovoltaic cells enables a certified power conversion efficiency of 25.2 per cent, translating to 80.5 per cent of the thermodynamic limit for its bandgap, which approaches those achieved by silicon solar cells., Author(s): Jason J. Yoo [sup.1] [sup.8] , Gabkyung Seo [sup.2] [sup.7] , Matthew R. Chua [sup.3] , Tae Gwan Park [sup.4] , Yongli Lu [sup.1] , Fabian Rotermund [sup.4] , [...]

Perovskite solar cells typically comprise electron- and hole-transport materials deposited on each side of a perovskite active layer. So far, only two organic hole-transport materials have led to state-of-the-art performance in these solar cells.sup.1: poly(triarylamine) (PTAA).sup.2-5 and 2,2E,7,7E-tetrakis(N,N-di-p-methoxyphenylamine)-9,9E-spirobifluorene (spiro-OMeTAD).sup.6,7. However, these materials have several drawbacks in terms of commercialization, including high cost.sup.8, the need for hygroscopic dopants that trigger degradation of the perovskite layer.sup.9 and limitations in their deposition processes.sup.10. Poly(3-hexylthiophene) (P3HT) is an alternative hole-transport material with excellent optoelectronic properties.sup.11-13, low cost.sup.8,14 and ease of fabrication.sup.15-18, but so far the efficiencies of perovskite solar cells using P3HT have reached only around 16 per cent.sup.19. Here we propose a device architecture for highly efficient perovskite solar cells that use P3HT as a hole-transport material without any dopants. A thin layer of wide-bandgap halide perovskite is formed on top of the narrow-bandgap light-absorbing layer by an in situ reaction of n-hexyl trimethyl ammonium bromide on the perovskite surface. Our device has a certified power conversion efficiency of 22.7 per cent with hysteresis of [plus or minus]0.51 per cent; exhibits good stability at 85 per cent relative humidity without encapsulation; and upon encapsulation demonstrates long-term operational stability for 1,370 hours under 1-Sun illumination at room temperature, maintaining 95 per cent of the initial efficiency. We extend our platform to large-area modules (24.97 square centimetres)--which are fabricated using a scalable bar-coating method for the deposition of P3HT--and achieve a power conversion efficiency of 16.0 per cent. Realizing the potential of P3HT as a hole-transport material by using a wide-bandgap halide could be a valuable direction for perovskite solar-cell research. A double-layered halide architecture for perovskite solar cells enables the use of dopant-free poly(3-hexylthiophene) as a hole-transport material, forming stable and scalable devices with a certified power conversion efficiency of 22.7 per cent., Author(s): Eui Hyuk Jung [sup.1] , Nam Joong Jeon [sup.1] , Eun Young Park [sup.1] , Chan Su Moon [sup.1] [sup.2] , Tae Joo Shin [sup.3] , Tae-Youl Yang [sup.1] [...]