Implementing an intermittent spin-coating strategy to enable bottom-up crystallization in layered halide perovskites

Two-dimensional halide perovskites (2D PVSKs) have drawn tremendous attentions owing to their outstanding ambient stability. However, the random orientation of layered crystals severely impedes the out-of-plane carrier transport and limits the solar cell performance. An in-depth understanding coupled with an effective control of the crystallization in 2D PVSKs is the crux for highly efficient and durable devices. In this contribution, we accidentally discovered that the crystallization of 2D PVSKs can be effectively regulated by so-called 'intermittent spin-coating (ISC)' process. Combined analyses of in(ex)-situ grazing-incidence wide-angle X-ray scattering with time-of-flight secondary ion mass spectrometry distinguish the interface initialized bottom-up crystallization upon ISC treatment from the bi-directional one in the conventional spin-coating process, which results in significantly enhanced crystal orientation and thus facilitated carrier transport as confirmed by both electrical measurements and ultrafast spectroscopies. As a result, the p-i-n architecture planar solar cells based on ISC fabricated paradigm PEA₂MA₃Pb₄I₁₃ deliver a respectable efficiency of 11.2% without any treatment, which is three-fold improvement over their spin-coated counterparts and can be further boosted up to 14.0% by NH₄Cl addition, demonstrating the compatibility of ISC method with other film optimization strategies.