Despite the impressive photovoltaic performances with power conversion efficiency beyond 22%, perovskite solar cells are poorly stable under operation, failing by far the market requirements. Various technological approaches have been proposed to overcome the instability problem, which, while delivering appreciable incremental improvements, are still far from a market-proof solution. Here we show one-year stable perovskite devices by engineering an ultra-stable 2D/3D (HOOC(CH2)4NH3)2PbI4/CH3NH3PbI3 perovskite junction. The 2D/3D forms an exceptional gradually-organized multi-dimensional interface that yields up to 12.9% efficiency in a carbon-based architecture, and 14.6% in standard mesoporous solar cells. To demonstrate the up-scale potential of our technology, we fabricate 10 × 10 cm2 solar modules by a fully printable industrial-scale process, delivering 11.2% efficiency stable for >10,000 h with zero loss in performances measured under controlled standard conditions. This innovative stable and low-cost architecture will enable the timely commercialization of perovskite solar cells.

Perovskites have been demonstrated in solar cells with power conversion efficiency well above 20%, which makes them one of the strongest contenders for the next generation photovoltaics. While there are no concerns about their efficiency, very little is known about their stability under illumination and load. Ionic defects and their migration in the perovskite crystal lattice are one of the most alarming sources of degradation, which can potentially prevent the commercialization of perovskite solar cells (PSCs). In this work, we provide direct evidence of electric field-induced ionic defect migration and we isolate their effect on the long-term performance of state-of-the-art devices. Supported by modelling, we demonstrate that ionic defects, migrating on timescales significantly longer (above 10 3 s) than what has so far been explored (from 10 -1 to 10 2 s), abate the initial efficiency by 10-15% after several hours of operation at the maximum power point. Though these losses are not negligible, we prove that the initial efficiency is fully recovered when leaving the device in the dark for a comparable amount of time. We verified this behaviour over several cycles resembling day/night phases, thus probing the stability of PSCs under native working conditions. This unusual behaviour reveals, that research and industrial standards currently in use to assess the performance and the stability of solar cells need to be adjusted for PSCs.Our work paves the way towards much needed new testing protocols and figures of merit specifically designed for PSCs.4

Organic–inorganic lead halide perovskites have shown photovoltaic performances above 20% in a range of solar cell architectures while offering simple and low-cost processability. Despite the multiple ionic compositions that have been reported so far, the presence of organic constituents is an essential element in all of the high-efficiency formulations, with the methylammonium and formamidinium cations being the sole efficient options available to date. In this study, we demonstrate improved material stability after the incorporation of a large organic cation, guanidinium, into the MAPbI3 crystal structure, which delivers average power conversion efficiencies over 19%, and stabilized performance for 1,000 h under continuous light illumination, a fundamental step within the perovskite field.

We demonstrate reduced charge recombination by formation of an engineered passivating layer, which leads to an enhanced power conversion efficiency of 21%.