We present new architectures in CH 3 NH 3 PbI 3 based planar perovskite solar cells incorporating solution processed SnO 2 /MgO composite electron transport layers that show the highest power outputs ever reported under typical 200-400 lx indoor illumination conditions. When measured under white OSRAM LED lamp (200, 400 lx), the maximum power density values were 20.2 µW/cm 2 (estimated PCE = 25.0% ) at 200 lx and 41.6 µW/cm 2 (PCE = 26.9%) at 400 lx which correspond to a  20% increment compared to solar cells with a SnO 2 layer only. The thin MgO overlayer leads to more uniform films, reduces interfacial carrier recombination, and leads to better stability. All layers of the cells, except for the two electrodes, are solution processed at low temperatures, thus low cost processing. Furthermore, ambient indoor conditions represent a milder environment compared to stringent outdoor conditions for a technology that is still looking for a commercial outlet also due to stability concerns. The unparalleled performance here demonstrated, paves the way for perovskite solar cells to contribute strongly to the powering of the indoor electronics of the future (e.g. smart autonomous indoor wireless sensor networks, internet of things etc). KEYWORDSelectron transport layer, SnO 2 layer, SnO 2 /MgO composite layer, planar perovskite solar cell, maximum power density, indoor light illumination.

To bring perovskite solar cells to the industrial world, performance must be maintained at the photovoltaic module scale. Here we present large-area manufacturing and processing options applicable to large-area cells and modules. Printing and coating techniques, such as blade coating, slot-die coating, spray coating, screen printing, inkjet printing, and gravure printing (as alternatives to spin coating), as well as vacuum or vapor based deposition and laser patterning techniques are being developed for an effective scale-up of the technology. The latter also enables the manufacture of solar modules on flexible substrates, an option beneficial for many applications and for roll-to-roll production.

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Paper is a flexible material, commonly used for information storage, writing, packaging or specialized purposes. It also has strong appeal as a substrate in the field of flexible printed electronics. Many applications, including safety, merchandising, smart labels/packing, chemical/biomedical sensors, require an energy source to power operation. Here we review progress regarding development of photovoltaic and energy storage devices on cellulosic substrates where one or more of the main material layers are deposited via solution processing or printing. Paper can be used simply as the flexible substrate or, exploiting its porous fibrelike nature, as an active film by infiltration or co-preparation with electronic materials. Solar cells with efficiencies of up to  4% on opaque and 9% on transparent substrates have been demonstrated. Recent developments in paper-based supercapacitors and batteries are also reviewed with maximum achieved capacity of 1350 mF cm -2 and 2000 mAh g -1 respectively.Analysing the literature, it becomes apparent that more work needs to be carried out in continuing to improve peak performance, but especially stability and the application of printing techniques, even roll-to-roll, over large areas. Paper is not only environmentally friendly and recyclable, it is thin, flexible, low-weight, biocompatible, and low-cost.

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markets for the more mature technologies, and research for the emerging technologies, are increasing year by year. Among these are organic, metal oxide, and organo-hybrid perovskite semiconductor transistor, light-emitting diode, and solar cell-based systems. [1][2][3][4] Large-area optoelectronics is developed on rigid (mainly on glass) and flexible (mainly on plastic such as polyethylene terephthalate, PET) substrates [5] with other types of substrates also being investigated such as paper, [6,7] flexible glass, [8] or textiles. [9] Organic lightemitting diodes (OLEDs), for example, are today one of the most commercialized technologies especially in small-display markets (e.g., smartphone displays) where they now take a major share of the market. In research laboratories, perovskite solar cells (PSC) have seen a huge interest reaching certified record efficiencies of 25.2% at standard test conditions (Air mass AM1.5G, 1000 W m −2 , 25 °C) [10] within only 10 years of development. Further they reach the highest power output densities under artificial indoor illumination (i.e., 20.2 µW cm −2 at 200 lx [11] ) which make them not only a bright candidate for energy harvesting outdoors but also for indoor IoT devices, sensors, and small consumer electronics [12] even for flexible substrates under artificial lighting. [13,14] The success of large area electronics in general lies in the advantageous properties of the materials used and in the fabrication processes (e.g., evaporation, sputtering or solution processing via printing techniques). These are also often compatible with flexible substrates. [15,16] Nevertheless, lifetimes of many of the constituent materials suffer when coming in contact with ambient moisture and oxygen [17][18][19] which can induce chemical degradation to the semiconducting, transport, and electrode layers. [20][21][22] To avoid moisture and oxygen ingress and further degradation, devices must be encapsulated with permeation barriers ensuring a water vapor transmission rate (WVTR) range of 10 −3 to 10 −6 g m −2 d −1 [23][24][25][26][27][28] and an oxygen transmission rate (OTR) between 10 −2 and 10 −5 cm 3 m −2 d −1 . [29][30][31][32] Encapsulation Effective transparent barrier/encapsulation systems represent a key enabling technology for large-area electronics. Securing stability to the environment is vital. Here, the effects of architectures, application processes, and water vapor transmission rates (WVTR) of transparent flexible ultra-high permeation barrier films (UHPBF) applied to substrates with adhesive resins are unraveled for attaining long lifetime, and compared with polyethylene terephthalate and glass barriers. How strongly performance of barrier/adhesive systems depends on barrier orientation, adhesion, manipulation, defects, and storage procedures is quantified via calcium tests. Furthermore, it is found that introducing an additional adhesion-promoting layer on the standard UHPBF stack reduces WVTRs by a factor of 5 compared to barriers without it. Finally, barriers are used fo...

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