Procedures and Practices for Evaluating Thin‐Film Solar Cell Stability

Abstract

functionality such as solution processing, have been the motivation driving these technologies. Additionally, compared to more conventional photovoltaics such as silicon solar cells, the device operation principles of many of these thin fi lm photovoltaic technologies are dependent on complex physical mechanisms, such as excitonic processes, photoinduced charge separation, functional material interfaces.Whereas initial research efforts were focused on understanding the underlying device physics and improvements in power conversion effi ciency, with increasing maturity of these photovoltaic technologies, growing efforts are now being invested into the understanding of underlying degradation mechanisms and the improvement of device stability. In addition to effi ciency, increased device lifetimes are fundamental requirements for transforming these technologies into an economic viability. In early studies, many stability investigations with various stress conditions were conducted in order to gain a better understanding of the degradation mechanisms. Currently, however, a consolidation towards some common stress scenarios for stability has been pursued in order to enable a better comparability between results of different research labs worldwide. A particularly well organized large scale effort was conducted within the framework of the International Summit on Organic Solar Cell Stability (ISOS), leading to the so-called ISOS-protocols. Nowadays, During the last few decades, and in some cases only the last few years, novel thin-fi lm photovoltaic (PV) technologies such as dye-sensitized solar cells (DSSC), organic solar cells (OPV), and, more recently, perovskite-based solar cells (PSC) have been growing in maturity with respect to device performance and device stability. Together with new material systems, novel device architectures have also been introduced. Both parameters will have an effect on the overall device stability. In order to improve the understanding of degradation effects and how they can be prevented, stress testing under different conditions is commonly applied. By careful combination of stress factors and thorough analysis of photovoltaic parameter decaying curves, an understanding of the underlying degradation pathways can be gained. With the help of standardized and accelerated stress tests, as described in the ISOS-protocols, statements concerning application lifetimes can fi nally be made and compared among different labs. Once a photovoltaic technology has proven long lasting durability, the ultimate barrier for entering the commercial market are the IEC tests, taking a deeper look on overall safety and reliability, not only on durability. Here, the most prominent stress tests are reviewed, discussed and extended with respect to learning the most about photovoltaic device stability.

UV-Induced Oxygen Removal for Photostable, High-Efficiency PTB7-Th:PC71BM Photovoltaic Cells

“…Such lifetimes obtained for cells subject to an ISOS-L-1 degradation test 23 correspond to one of the few cases where high efficiency polymer solar cells exhibit a remarkable photo-stability.…”

“…Indeed, beyond the effect of the burn-in, for all four cases under consideration the device evolution dynamics can be adjusted to a single exponential decay, as seen in Figure S4. 23 The decay time for the reference cell was determined to be less than two thousand hours while for the other three cells the decay time is about two times larger, being the decay time for the UVN-treated device the largest one, as seen in Table S2. The three cells with a molecular-oxygen-free ETL exhibited T 80 lifetimes in the 500-550 hours range, while that for the reference T 80 lifetime for was close to 2.5 times smaller as seen in Table 1.…”

Toward High‐Temperature Stability of PTB7‐Based Bulk Heterojunction Solar Cells: Impact of Fullerene Size and Solvent Additive

“…[1][2][3][4][5][6][7] Despite these strong technological improvements, the insufficient stability is still a limiting factor for commercialization of PSCs. [8][9][10][11][12] Thus one of the key challenges of PSC technology is to overcome thermal instability of organic solar cells. Industrial standards demand for high-throughput roll-to-roll processing that usually requires several heating steps at high temperature to evaporate solvents from the printed layers.…”

The Emergence of the Mixed Perovskites and Their Applications as Solar Cells

“…[41] Moreover, MAPbI 3 has been reported to experience thermally-induced degradation at temperatures above 85 °C, at which the accelerated stress tests for a commercial solar cell are applied, according to ISOSprotocols. [42,43] Second, the bandgap of MAPbI 3 , 1.55 eV, is not optimal for maximized utilization of solar energy according to Shockley-Queisser (S−Q) theory. [44] The MAPbI 3 absorber shows a high absorption coefficient only for photons above 800 nm, which impede the further improvement of PCE.…”