Vol.:(0123456789) 1 3 Journal of Materials Science: Materials in Electronics https://doi.org/10.1007/s10854-019-01292-2 Photo‑stability of perovskite solar cells with Cu electrode Abhishek K. Chauhan 1,2  · Pankaj Kumar 1,2 Received: 24 November 2018 / Accepted: 6 April 2019 © Springer Science+Business Media, LLC, part of Springer Nature 2019 Abstract Towards higher stability of perovskite solar cells, Cu has been observed to be more suitable electrode material compared to conventional Al and Ag electrodes. The photo-stability of such devices has not been explored much in the literature, therefore we present here the investigation carried out towards the photo-stability of PSCs based on top Cu electrodes. The PSCs were prepared in normal geometry and stored in dark, under continuous illumination of a white LED lamp inside the laboratory and under direct sunlight outside the laboratory and tested as per the international summit on organic photovoltaics stabil- ity protocols. In dark storage the encapsulated solar cells exhibited highest stability but under illumination they exhibited degradation in their performance and the degradation was fastest in the direct sunlight. Degradation under illumination has been attributed to the photo-oxidation of the perovskite film. Cu has been observed to diffuse into and react with the underlying perovskite film and the ultraviolet and infrared contents in direct sunlight accelerated the photo-oxidation and chemical reactions between Cu and perovskite film. The chemical reactions of Cu electrode with perovskite constituents made it disappear after some time. These investigations suggest that Cu too is not a very stable electrode material for PSCs under natural operating conditions. 1 Introduction Organo-metal halide perovskite semiconductors have shown enormous potential for efficient and cost effective conver- sion of solar energy into electricity and have now become the materials of high importance for energy conversion [1]. These materials have extraordinary electrical and opti- cal properties and the power conversion efficiency (PCE) of perovskite solar cells (PSCs) has gone beyond 23% [2], approaching to that of the conventional Si solar cells. Inte- gration of PSCs with Si solar cells in tandem structures has shown PCE over 26% [3–5] and it is expected that the PCE of such devices can easily go beyond 30% [6]. But before this technology is considered for real market products, its scalable fabrication and long term stability are the major issues that need to be sorted out. Usually PSCs are prepared via spin coating technique but some efforts have also been made to prepare perovskite films via well established scal- able solution deposition techniques like spray coating [7], doctor blade coating [8], slot die coating [9] and screen printing [10]. Since PSCs incorporate the layers of multiple materials like light absorber, charge transport materials and electrodes, the process for large scale production of com- plete optimized structure is yet to be realized. Performance of PSCs is very sensitive to materials purities, processing conditions and growth methods. A little variation in these parameters leads to a very large variation in the device per- formance, so the performance is optimized very carefully. PSCs have shown to degrade and lose their photovoltaic properties at high temperatures and when exposed to oxygen, moisture and UV light [11–14]. It is observed that the water molecules hydrolyse the perovskites and break them into their precursors. For example, in the presence of H 2 O mol- ecules methyl ammonium lead iodide (CH 3 NH 3 PbI 3 ) breaks down into CH 3 NH 3 I (MAI) and lead iodide (PbI 2 ), while MAI further breaks down into CH 3 NH 2 and HI [15, 16]. The decomposition of perovskites gets accelerated at high tem- peratures and in the presence of UV light [17]. Though the molecular decomposition can be overcome to some extent via molecular engineering [18–20], compositional engineer- ing [21, 22] or using the cross linking additives in the pre- cursors [23], but it is not only the perovskite materials that * Pankaj Kumar pankaj@nplindia.org 1 Advanced Materials and Devices Metrology Division, CSIR- National Physical Laboratory, Dr. K. S. Krishnan Marg, New Delhi 110012, India 2 Academy of Scientific and Innovative Research (AcSIR), Ghaziabad 201002, India