Perovskite Solar Cells (PSCs) are well known for their high efficiencies under 1 sun (AM1.5G), however, PSC can also generate power by harvesting the low‐light available indoors. Here, three flexible PSC architectures are presented for indoor applications: with a metal electrode aiming for high efficiency; carbon electrode aiming for high stability and compatibility with large‐scale production; and hole transport material (HTM)‐free carbon for simplifying the fabrication process. A maximum efficiency of 30.9% (30.0%) under 1000 lux (200 lux) is obtained for a PSC with gold electrode. A maximum efficiency of 25.4% (24.7%) and 23.1% (22.3%) is obtained for the carbon devices with and without HTM, respectively, under 1000 lux (200 lux). To the best of the author's knowledge, the efficiency values presented here for a device with a carbon‐based electrode, with and without HTM, are the record values for a flexible PSC at indoor light conditions. Furthermore, the HTM‐free carbon device kept 84% of its initial efficiency after 1000 h at MPPT and lost virtually no performance after 1000 h at 85 °C. Also, non‐encapsulated devices of all configurations withstood 1600 h in air with a maximum loss in efficiency of 6%.

Hybrid organic-inorganic perovskite materials have become one of the most studied classes of light-harvesting materials due to their exceptional properties such as high light absorption, long carrier diffusion lengths, bandgap tuning and defect tolerance. Since 2009 that the scientific community has been working on improving the power conversion efficiency (PCE) of perovskite solar cell devices, reaching now an impressive value of 25.5%. Moreover, efficiencies over 18% are often reported by several authors. Since the efficiency goal is almost fulfilled, the scientific community is currently addressing five challenges, with the ultimate objective to make this technology competitive and turn it commercial; these challenges are cost, stability, upscaling, safety and environmental impact.Given the astonishing progresses reached during the past decade and the numerous research groups working to the same goal, it is a matter of time until commercial perovskite solar devices become a reality. In this review work, the most recent achievements regarding this purpose are put together and compared, so as to suggest the most suitable perovskite solar fabrication processes and materials to produce commercial devices.

Summary Perovskite solar cells are one of the most promising photovoltaic technology, presenting the fastest power conversion efficiency (PCE) growth from 3.8 % to 24.2 % in just 10 years. However, there are still challenges hindering its commercialization such as the expensive back‐contact made of gold. Carbon‐based materials, mainly carbon pastes made of carbon black and graphite, have already proven to be good candidates as back‐contacts because of their features such as low cost, high conductivity, and high stability. In this work, the replacement of gold back‐contact by a carbon paper with a microporous layer coated with a PEDOT:PSS dispersion is reported. To the best of the author's knowledge, this material has never been reported for perovskite solar cells. A PCE of 9.22 % was obtained, representing 62 % of the PCE obtained for the same cell but with a gold back‐contact.

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