Nanoscale Spatial and Transient Mapping of Charge Carriers for Operationally Stable MA-Free Perovskite Solar Cells

Perovskite solar cells (PSCs) have shown great potential to yield high power conversion efficiency surpassing 26.1% for single junction and 33.7% in tandem PSC/Si device yet retaining such performance under continuous operation has remained elusive. Understanding the nanoscopic photochemical changes that drive instabilities in perovskite semiconductors is critical for mitigating device degradation. We develop a multimodal technique to reveal the photodynamic disorder in methylammonium (MA)-free wide-bandgap perovskites leading to the poor radiative efficiency and meager device performance at high temperatures.

Transient Photo-response atomic force microscopy (TP-AFM) is used to spatially map the surface topography and transient map for photodynamics such as recombination lifetime (t_r), transport time (t_t) and diffusion length (L_D) in wide-bandgap PSCs operative at high temperatures. We visualize the changes in the heat-induced structural changes associated with the carrier trapping through grain interiors and grain boundaries that affect the device longevity.  Importantly, we discover that both performance losses and intrinsic degradation processes can be mitigated by modulating the composition of active layer absorber with the fine tuning of its chemical properties. This multimodal workflow to correlate the nanoscale landscape of photodynamics and topography evaluation will be applicable to other analogous perovskite compositions for which a local depiction of performance and operational stability has yet to be recognized.