Revealing two heat-annealing related photoproduct systems and widely existed subgrain domains in organolead perovskite

TL;DR

This study reveals heat-annealing induces new photoproduct systems and subgrain domains in organolead perovskite films, impacting their morphology and potentially enhancing solar cell performance.

Contribution

It uncovers heat-annealing related photoproduct systems and subgrain domains, providing insights into the morphological basis for high-performance perovskite layers.

Findings

Heat-annealing creates a new emissive exciton-carrier collision system.

Subgrain domains are broadly present in heat-annealed perovskite films.

The morphological changes relate to improved device performance.

Abstract

For highly interested organolead perovskite based solar cells, the photoproducts are regarded as the co-existed exciton and free carriers. In this study, we carefully re-examined this conclusion with our recently developed density-resolved spectroscopic method. Heat-annealing related two photoproduct systems are observed. We found that the widely accepted model is only true for single crystal and freshly made films without heat-annealing. For those sufficiently heat-annealed films, another system presenting significant emissive exciton-carrier collision (ECC) is discovered. In addition, the appearing of ECC indicates the emerging of an internal morphology after heat annealing, which is assigned to a recently discussed twinning subgrain structure. We proved that such subgrain structures broadly exist in perovskite films. This finding could prove the morphological basis for high performance of perovskite working layers.