# Impact of precursor solution temperature on two-step spin-coated FAPbI3 film elucidated by surface morphology and in situ photoluminescence dynamics

## TL;DR

This study shows how adjusting the temperature of precursor solutions during film formation affects the quality and performance of perovskite solar cells.

## Contribution

The study identifies optimal precursor solution temperatures for achieving high-quality FAPbI3 films using two-step spin-coating.

## Key findings

- Intermediate PbI2 solution temperatures (50–70 °C) produce compact underlayers that reduce residual PbI2.
- Low-temperature FAI solutions stabilize the photoactive α-phase of FAPbI3.
- In situ PL monitoring links crystallization stages to optical properties.

## Abstract

Perovskite solar cells fabricated by the two-step spin-coating method are highly sensitive to processing conditions, yet the role of precursor solution temperature remains poorly understood. Here, we systematically investigate how the temperatures of PbI2 and formamidinium iodide (FAI) precursor solutions affect crystallization dynamics, surface morphology, phase formation, and optoelectronic properties of FAPbI3 thin films. By combining microscopic characterization with in situ photoluminescence (PL) monitoring during annealing, we reveal distinct temperature-dependent nucleation, ripening, and film densification processes. PbI2 solutions at intermediate temperatures (50–70 °C) yield compact underlayers that promote homogeneous conversion and suppress residual PbI2, while low-temperature FAI solutions favor stabilization of the photoactive α-phase. Quantitative analysis of the in situ PL evolution clarifies the correlation between crystallization stages and optical out-coupling behavior. These results establish precursor solution temperature as a critical and practical parameter for controlling perovskite film formation in two-step deposition processes.

Precursor solution temperature governs crystallization, morphology, and phase formation in two-step spin-coated FAPbI3 films. In situ PL reveals nucleation behavior, showing that 50–70 °C for PbI2 and ∼25 °C for FAI yield compact α-phase films.