Stress Engineering for Mitigating Thermal Cycling Fatigue in Perovskite Photovoltaics

Mechanical residual stresses within multilayer thin-film device stacks become problematic during thermal changes because of differing thermal expansion and contraction of the various layers. Thin-film photovoltaic (PV) devices are a prime example where this is a concern during temperature fluctuations that occur over long deployment lifetimes. Here, we show control of the residual stress within halide perovskite thin-film device stacks by the use of an alkyl-ammonium additive. This additive approach reduces the residual stress and strain to near-zero at room temperature and prevents cracking and delamination during intense and rapid thermal cycling. We demonstrate this concept in both n-i-p (regular) and p-i-n (inverted) unencapsulated perovskite solar cells and minimodules with both types of solar cells retaining over 80% of their initial power conversion efficiency (PCE) after 2500 thermal cycles in the temperature range of -40 to 85 degrees C. The mechanism by which stress engineering mitigates thermal cycling fatigue in these perovskite PVs is discussed.