Perovskite solar cells (PSCs) have shown great potential for next-generation photovoltaics. One of the main barriers to their commercial use is their poor long-term stability under ambient conditions and, in particular, their sensitivity to moisture and oxygen. Therefore, several encapsulation strategies are being developed in an attempt to improve the stability of PSCs in a humid environment. The lack of common testing procedures makes the comparison of encapsulation strategies challenging. In this paper, we optimized and investigated two common encapsulation strategies: lamination-based glass–glass encapsulation for outdoor operation and commercial use (COM) and a simple glue-based encapsulation mostly utilized for laboratory research purposes (LAB). We compare both approaches and evaluate their effectiveness to impede humidity ingress under three different testing conditions: on-shelf storage at 21 °C and 30% relative humidity (RH) (ISOS-D1), damp heat exposure at 85 °C and 85% RH (ISOS-D3), and outdoor operational stability continuously monitoring device performance for 10 months under maximum power point tracking on a roof-top test site in Berlin, Germany (ISOS-O3). LAB encapsulation of perovskite devices consists of glue and a cover glass and can be performed at ambient temperature, in an inert environment without the need for complex equipment. This glue-based encapsulation procedure allowed PSCs to retain more than 93% of their conversion efficiency after 1566 h of storage in ambient atmosphere and, therefore, is sufficient and suitable as an interim encapsulation for cell transport or short-term experiments outside an inert atmosphere. However, this simple encapsulation does not pass the IEC 61215 damp heat test and hence results in a high probability of fast degradation of the cells under outdoor conditions. The COM encapsulation procedure requires the use of a vacuum laminator and the cells to be able to withstand a short period of air exposure and at least 20 min at elevated temperatures (in our case, 150 °C). This encapsulation method enabled the cells to pass the IEC 61215 damp heat test and even to retain over 95% of their initial efficiency after 1566 h in a damp heat chamber. Above all, passing the damp heat test for COM-encapsulated devices translates to devices fully retaining their initial efficiency for the full duration of the outdoor test (>10 months). To the best of the authors’ knowledge, this is one of the longest outdoor stability demonstrations for PSCs published to date. We stress that both encapsulation approaches described in this work are useful for the scientific community as they fulfill different purposes: the COM for the realization of prototypes for long-term real-condition validation and, ultimately, commercialization of perovskite solar cells and the LAB procedure to enable testing and carrying out experiments on perovskite solar cells under noninert conditions.

Over the past decade, perovskite solar cells have travelled an amazing way towards high efficiency. However, a major roadblock remaining is the operational stability, while achieving technological maturity and proving real-world stability is crucial to gain trust among investors. In that sense, it is of high interest to be able to predict the operational lifetime, which needs to be in the range of years or decades, within an experimentally reasonable timeframe. Yet, peculiarities of perovskite solar cells’ ageing behaviour lead to severe difficulties in translating the results of indoor tests to their outdoor counterpart. In particular, transient processes cause diverse results among different ageing tests.Here, for the first time, we show a complete set of constant illumination indoor testing, cycled illumination indoor testing and real-world outdoor testing on equal in-house devices. Exemplarily, we compare two different types of perovskite solar cells, in which only the hole-transport layer is varied. Despite this small change, the devices show distinctly different transient behaviour. In either case, the commonly used constant illumination experiments fail to predict the outdoor behaviour of the cell. Yet, we observe a good correlation between the cycled illumination test and the outdoor behaviour of one of the two solar cells, while this is not the case for the other system. This result highlights the urge for further research on how to perform meaningful accelerated indoor tests to predict the outdoor lifetime of perovskite solar cells.

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