The area of thin-film photovoltaics has been overwhelmed by organometal halide perovskites. Unfortunately, serious stability concerns arise with perovskite solar cells. For example, methyl-ammonium lead iodide is known to decompose in the presence of water and, more severely, even under inert conditions at elevated temperatures. Here, we demonstrate inverted perovskite solar cells, in which the decomposition of the perovskite is significantly mitigated even at elevated temperatures. Specifically, we introduce a bilayered electron-extraction interlayer consisting of aluminium-doped zinc oxide and tin oxide. We evidence tin oxide grown by atomic layer deposition does form an outstandingly dense gas permeation barrier that effectively hinders the ingress of moisture towards the perovskite and—more importantly—it prevents the egress of decomposition products of the perovskite. Thereby, the overall decomposition of the perovskite is significantly suppressed, leading to an outstanding device stability.

No abstract

Semitransparent perovskite solar cells (PSCs) are of interest for application in tandem solar cells and building-integrated photovoltaics. Unfortunately, several perovskites decompose when exposed to moisture or elevated temperatures. Concomitantly, metal electrodes can be degraded by the corrosive decomposition products of the perovskite. This is even the more problematic for semitransparent PSCs, in which the semitransparent top electrode is based on ultrathin metal films. Here, we demonstrate outstandingly robust PSCs with semitransparent top electrodes, where an ultrathin Ag layer is sandwiched between SnO x grown by low-temperature atomic layer deposition. The SnO x forms an electrically conductive permeation barrier, which protects both the perovskite and the ultrathin silver electrode against the detrimental impact of moisture. At the same time, the SnO x cladding layer underneath the ultra-thin Ag layer shields the metal against corrosive halide compounds leaking out of the perovskite. Our semitransparent PSCs show an efficiency higher than 11% along with about 70% average transmittance in the near-infrared region (λ > 800 nm) and an average transmittance of 29% for λ = 400-900 nm. The devices reveal an astonishing stability over more than 4500 hours regardless if they are exposed to ambient atmosphere or to elevated temperatures.

Transparent and electrically conductive gas diffusion barriers are reported. Tin oxide (SnOx ) thin films grown by atomic layer deposition afford extremely low water vapor transmission rates (WVTR) on the order of 10(-6) g (m(2) day)(-1) , six orders of magnitude better than that established with ITO layers. The electrical conductivity of SnOx remains high under damp heat conditions (85 °C/85% relative humidity (RH)), while that of ZnO quickly degrades by more than five orders of magnitude.

In organic solar cells (OSCs), the necessity of UV activation that comes with the use of ZnO‐ and TiOx‐based electron extraction layers (EELs) can be avoided by using tin oxide (SnOx), which can be prepared at temperatures as low as 80 °C. In contrast to devices based on TiOx and ZnO, OSCs comprising SnOx as the EEL show well‐behaved solar cell characteristics with a high fill factor (FF) and high efficiency, even without the UV spectral range of the AM1.5 solar spectrum.

Corrosive precursors used for the preparation of organic-inorganic hybrid perovskite photoactive layers prevent the application of ultrathin metal layers as semitransparent bottom electrodes in perovskite solar cells (PVSCs). This study introduces tin-oxide (SnO ) grown by atomic layer deposition (ALD), whose outstanding permeation barrier properties enable the design of an indium-tin-oxide (ITO)-free semitransparent bottom electrode (SnO /Ag or Cu/SnO ), in which the metal is efficiently protected against corrosion. Simultaneously, SnO functions as an electron extraction layer. We unravel the spontaneous formation of a PbI interfacial layer between SnO and the CH NH PbI perovskite. An interface dipole between SnO and this PbI layer is found, which depends on the oxidant (water, ozone, or oxygen plasma) used for the ALD growth of SnO . An electron extraction barrier between perovskite and PbI is identified, which is the lowest in devices based on SnO grown with ozone. The resulting PVSCs are hysteresis-free with a stable power conversion efficiency (PCE) of 15.3% and a remarkably high open circuit voltage of 1.17 V. The ITO-free analogues still achieve a high PCE of 11%.

Despite the notable success of hybrid halide perovskite-based solar cells, their long-term stability is still a key-issue. Aside from optimizing the photoactive perovskite, the cell design states a powerful lever to improve stability under various stress conditions. Dedicated electrically conductive diffusion barriers inside the cell stack, that counteract the ingress of moisture and prevent the migration of corrosive halogen species, can substantially improve ambient and thermal stability. Although atomic layer deposition (ALD) is excellently suited to prepare such functional layers, ALD suffers from the requirement of vacuum and only allows for a very limited throughput. Here, we demonstrate for the first time spatial ALD-grown SnO at atmospheric pressure as impermeable electron extraction layers for perovskite solar cells. We achieve optical transmittance and electrical conductivity similar to those in SnO grown by conventional vacuum-based ALD. A low deposition temperature of 80 °C and a high substrate speed of 2.4 m min yield SnO layers with a low water vapor transmission rate of ∼10 gm day (at 60 °C/60% RH). Thereby, in perovskite solar cells, dense hybrid Al:ZnO/SnO electron extraction layers are created that are the key for stable cell characteristics beyond 1000 h in ambient air and over 3000 h at 60 °C. Most notably, our work of introducing spatial ALD at atmospheric pressure paves the way to the future roll-to-roll manufacturing of stable perovskite solar cells.

low fi ll-factors (FFs) and overall low power conversion efficiency are found. This phenomenon is frequently referred to as "light-soaking" issue. [ 31,32 ] Development of charge extraction materials that do not rely on UV activation has been identifi ed to be of paramount importance to achieve highly effi cient and long-term stable devices. [ 33,34 ] In this sense, doped metaloxide EELs, e.g., Al:ZnO, [ 31,35,36 ] have been shown to mitigate the need for UV activation. While there are several reports of OSCs incorporating ZnO-based EELs in organic solar cells, which show a promising "shelf-life," [ 37 ] photoinduced shunts have been found to occur in the devices upon illumination "in actual operation." [38][39][40] Analogous to the case of the light activation discussed above, these photoinduced shunts are associated with the illumination by UV light (i.e., hν > E g ). As a result, a signifi cantly lowered shunt resistance along with a substantial decay of the FF and V oc is typically found to occur within minutes of illumination. The origin of this photoinduced shunt has been related to the UV-induced desorption of chemisorbed oxygen at the ZnO surface. [ 38 ] Approaches to modify and thereby to stabilize the ZnO surface range from the use of passivating mole cules [ 41 ] to the evaporation of thin aluminum layers onto the ZnO EEL. [ 39 ] Here, we will show that the photoinduced shunting behavior is a general phenomenon in OSCs comprising "neat or electrically doped" ZnO-based electron extraction layers, i.e., Al:ZnO (AZO) or Ga:ZnO (GZO), and it is found regardless if the EEL is prepared from nanoparticle dispersions or by vacuumbased techniques ( Figure 1 ). The photoinduced shunting of ZnO-based OSCs occurs for devices operated in air or under inert atmosphere, and it can therefore not be avoided by using a proper encapsulation. Moreover, we will show that while the photoinduced shunting is reversible in air, it is irreversible under the exclusion of oxygen. Opposed to ZnO-based EELs, we will demonstrate that the photoinduced shunting and the con-