Perovskite solar cells (PSC) with efficiencies > 20% have only been realized with highly expensive archetype organic hole transporting materials that can impede the large-scale deployment of PSC. Here we demonstrate PSCs achieving stabilized efficiencies of 20.3% with CuSCN as hole electron extraction layer. We developed a new method for the solution deposition of compact and highly conformal CuSCN layers that afford fast carrier extraction and collection. We also show that the notorious instability of CuSCN based PSCs is not associated with the CuSCN/perovskite interface but rather originates from the CuSCN/Au contact. By introducing a thin spacer layer between CuSCN and gold layers, the PSCs retained >95% of their initial efficiency after aging for 500 h under full-sun illumination at 60 °C, and >85% of their initial efficiency after aging at 85 °C for 1000 h. Importantly, under both continuous illumination and thermal stress, CuSCN based devices surpass the stability of spiro-OMeTAD based PSCs.One Sentence Summary: A record performance displayed by operationally stable perovskite solar cells employing all-inorganic charge extraction layers was realized after introducing a simple dynamic approach for the deposition of thin and conformal CuSCN layer onto perovskite layer and a thin spacer layer between CuSCN and gold layers, which will foster their large scale deployment.The prominence of organic-inorganic perovskite solar cells (PSC) can be credited to the unprecedented advancement in the power conversion efficiencies (PCEs), realized mostly by tailoring the formation and composition of the absorber layer (1,2). Certified PCEs >20% have been obtained while retaining the electron selective TiO 2 layer and by using either spiroOMeTAD [2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenyl-amine)9,9′-spirobifluorene] or a polymerbased PTTA (poly-triarylamine) as the hole-transporting material (HTM) (2,3). However, the cost of these HTMs is prohibitively high for large-scale applications and the long-term operational and thermal instability seems to be associated with the archetype organic HTMs or their ingredients (4). One of the strategies to combat the issues of cost and instability could be the use of inexpensive inorganic hole extraction layers similar to the use of TiO 2 as an electron transporting material (5). However, obtaining stable PCEs >20% with PSCs using inorganic 2 HTMs, such as NiO, CuI, Cs 2 SnI 6 , and CuSCN when subjected to light soaking under realistic operational conditions, i.e., at maximum power point and 60°C has remained a challenge (6-9).The realization of efficiencies > 20% using PSCs with inorganic HTMs remains undoubtedly a key goal to foster the large-scale deployment of PSC. Among various inorganic hole transporting materials, CuSCN is an extremely cheap, abundant p-type semiconductor, that exhibits high hole mobility, a good thermal stability and a well-aligned work function (10). The CuSCN is intrinsically p-doped and transmits light across the entire visible and near infrared spect...

Preventing the degradation of metal perovskite solar cells (PSCs) by humid air poses a substantial challenge for their future deployment. We introduce here a two-dimensional (2D) A2PbI4 perovskite layer using pentafluorophenylethylammonium (FEA) as a fluoroarene cation inserted between the 3D light-harvesting perovskite film and the hole-transporting material (HTM). The perfluorinated benzene moiety confers an ultrahydrophobic character to the spacer layer, protecting the perovskite light-harvesting material from ambient moisture while mitigating ionic diffusion in the device. Unsealed 3D/2D PSCs retain 90% of their efficiency during photovoltaic operation for 1000 hours in humid air under simulated sunlight. Remarkably, the 2D layer also enhances interfacial hole extraction, suppressing nonradiative carrier recombination and enabling a power conversion efficiency (PCE) >22%, the highest reported for 3D/2D architectures. Our new approach provides water- and heat-resistant operationally stable PSCs with a record-level PCE.

Organic-inorganic lead halide perovskites have unusual, temperature-dependent emission characteristics.

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As the photovoltaic performance of a device is strongly influenced by the morphology of perovskite, achieving precise control over the crystal formation of organic-inorganic halide perovskites synthesized in the ambience of chloride ions has garnered much attention. Although the resulting morphology dictates the performance of the device considerably, the understanding of the role of chloride ions has been scant. To unravel this mystery, we investigated three different organic-inorganic halide perovskite materials grown from the chloride-containing precursors under different but optimized conditions. Despite the presence of chloride ions in the reaction mixture, scanning transmission electron microscopy- energy dispersive spectroscopy (STEM-EDS) reveals that the CH3NH3PbI3 perovskites formed are chloride-free. Moreover bright field transmission electron microscopy indicates that chloride ions effect the growth of the CH3NH3PbI3.

Lead halide perovskite solar cells now show excellent efficiencies and encouraging levels of stability. Further improvements in performance require better control of the trap states which are considered to be associated with vacancies and defects at crystallite surfaces. Herein, a reflection on the ways in which these traps can be mitigated is presented by improving the quality of the perovskite layer and interfaces in fully assembled device configurations. In this review, the most recent design strategies reported in the literature, which have been explored to tune grain orientation, to passivate defects, and to improve charge‐carrier lifetimes, are presented. Specifically, the advances made with single‐cation, mixed‐cation and/or mixed‐halide, and 3D/2D bilayer‐based light absorbers are discussed. The interfacial, compositional, and band alignment engineering along with their consequent effects on the open‐circuit voltage, power conversion efficiency, and stability are a particular focus.

We report the influence of monovalent cation halide additives on the optical, excitonic and electrical properties of CH 3 NH 3 PbI 3 perovskite. Monovalent cation halide with similar ionic radii to Pb 2+ , including Cu + , Na + and Ag + , were added to explore possibility of doping. We observed significant reduction of subbandgap optical absorption and lower energetic disorder along with a shift in the Fermi level of the perovskite in the presence of these cations. The bulk hole mobility of the additive based perovskites as estimated using the space charge limited current method exhibited an increase of up to an order of magnitude compared to the pristine perovskites with a significant decrease in the activation energy.Consequentially, enhancement in the photovoltaic parameters of additive-based solar cells was achieved.We observed an increase in open circuit voltage for AgI (~1.02 vs 0.95 V for the pristine) and photocurrent density for NaI and CuBr based solar cells (≈23 vs 21 mA.cm -2 for the pristine). This enhanced photovoltaic performance could be attributed to the formation of uniform and continuous perovskite film, better conversion and loading of perovskite as well as the enhancement in the bulk charge transport along with a minimization of disorder, pointing towards possible surface passivation.

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