Efficient monolithic perovskite/perovskite tandem solar cells are fabricated using two perovskite absorbers with complementary bandgaps. By employing doped organic semiconductors, an efficient and selective extraction of the charge carriers is ensured. This study demonstrates perovskite/perovskite tandem cells delivering a maximum efficiency of 18%, highlighting the potential of vacuum‐deposited multilayer structures in overcoming the efficiency of single‐junction perovskite devices.

Vacuum deposition is one of the most technologically relevant techniques for the fabrication of perovskite solar cells. The most efficient vacuum-based devices rely on doped organic contacts, compromising the long-term stability of the system. Here, we introduce an inorganic electron-transporting material to obtain power conversion efficiencies matching the best performing vacuum-deposited devices, with open-circuit potential close to the thermodynamic limit. We analyze the leakage current reduction and the interfacial recombination improvement upon use of a thin (<10 nm) interlayer of C, as well as a more favorable band alignment after a bias/ultraviolet light activation process. This work presents an alternative for organic contacts in highly efficient vacuum-deposited perovskite solar cells.

The addition of Sr in CH NH PbI perovskite films enhances the charge carrier collection efficiency of solar cells leading to very high fill factors, up to 85%. The charge carrier lifetime of Sr -containing perovskites is in excess of 40 μs, longer than those reported for perovskite single crystals.

In this section the governing equations of the drift-diffusion model implemented in Setfos 4.6 1 are explained. The quantities are described in the next section.

Methylammonium lead triiodide (MAPI) has emerged as a high‐performance photovoltaic material. Common understanding is that at room temperature, it adopts a tetragonal phase and it only converts to the perfect cubic phase around 50–60 °C. Most MAPI films are prepared using a solution‐based coating process, yet they can also be obtained by vapor‐phase deposition methods. Vapor‐phase‐processed MAPI films have significantly different characteristics than their solvent‐processed analogous, such as relatively small crystal‐grain sizes and short excited‐state lifetimes. However, solar cells based on vapor‐phase‐processed MAPI films exhibit high power‐conversion efficiencies. Surprisingly, after detailed characterization it is found that the vapor‐phase‐processed MAPI films adopt a cubic crystal structure at room temperature that is stable for weeks, even in ambient atmosphere. Furthermore, it is demonstrated that by tuning the deposition rates of both precursors during codeposition it is possible to vary the perovskite phase from cubic to tetragonal at room temperature. These findings challenge the common belief that MAPI is only stable in the tetragonal phase at room temperature.

Vacuum deposition of perovskite solar cells can achieve efficiencies rivaling solution-based methods and allows for more complex device stacks. MoO3 has been used to enhance carrier extraction to the transparent bottom electrode in a p-i-n configuration; here, we show that by inserting an molecular interlayer with a lone pair nitrogen atom and low ionization potential, it can also be used on the top of a perovskite absorber in a n-i-p configuration. This strategy enables the first vacuum-deposited perovskite solar cells with metal oxides as charge transporting layers for both electrons and holes, leading to power conversion efficiency >19%.

We study the properties of the series of compounds Cs0.15FA0.85Pb(BrxI1−x)3, aiming to develop an efficient complementary absorber for MAPbI3 in all-perovskite tandems. A bromide content of 0.7 leads to a band gap of 2 eV and a maximum PCE of 11.5% in solar cells, among the highest reported for band gaps wider than 1.8 eV.

Methylammonium lead iodide (MAPI) has proven to be an exceptional light-absorber for single-junction thin-film solar cells. Nonetheless, degradation induced by environmental agents (air, moisture, heat) limits the stability of this hybrid perovskite. Here, we demonstrate that coating evaporated MAPI thin films with different hydrophobic molecules leads to a significant improvement in their stability. We especially investigated the degradation of MAPI and the subsequent formation of PbI 2 at 150°C by in situ XRD analysis and showed that this transformation is remarkably slowed down in films coated with trioctyl phosphine oxide and tridodecyl methylammonium iodide. This enhances the processability of such films, which is an important aspect for the fabrication of thin-film devices. Eventually, we demonstrate that such protected films can be implemented in single-junction n−i−p solar cells without any loss in the device efficiency. A s widely reported in the past few years, methylammonium lead iodide (CH 3 NH 3 PbI 3 ; MAPI) is an excellent material for single-junction solar cells and other optoelectronic devices. 1−4 The outstanding performances of these devices can be linked to several photophysical properties of perovskites, such as their high absorption coefficient, narrow bandgap, and high charge diffusion lengths, 5,6 together with the ease of fabrication and low cost of precursors. 7 Nonetheless, the widespread use of MAPI is currently severely hindered by its well-known instability. Indeed, oxygen, water (moisture), and heat among other factors are known to lead to a fast degradation of MAPI thin films. 8,9 In order to mitigate this instability, one possible approach is to alter the material composition, as already demonstrated in many reports. These modifications include the partial substitution of I − anions with Br − anions, 10 the partial or total substitution of MA cations with other organic or inorganic monovalent cations such as formamidinium (CH(NH 2) 2 + ; FA), cesium (Cs +), or rubidium (Rb +), 11−13 or the incorporation of 2D perovskites. 14−18 These substitutions can lead to rather complex formulations comprising up to seven different ions whose relative amounts 47 need to be well controlled. 19 Furthermore, bromide-based and 48 2D perovskites have a higher bandgap than their 3D iodide 49 counterparts, which is not beneficial for photovoltaic (PV) 50 applications. 14−18 Hence, it is critical to explore new ways of 51 enhancing the stability of MAPI films without necessarily 52 altering their overall composition. Because degradation often 53 initiates at the surface of the films through its exposure to 54 external species (e.g., moisture), 20 one possible strategy is to 55 chemically modify the perovskite surface with different organic 56 molecules. Yang et al. 21 showed that coating the surface of 57 solution-processed MAPI thin films with different hydrophobic 58 molecules leads to an increased stability in a high-moisture 59 environment at room temperature. The same approach has 60 recently bee...