Toward Scalable and Sustainable Perovskite Solar Cells: Optimizing Atmospheric-Pressure Spatial Atomic Layer Deposition SnOX for Enhanced Perovskite Crystallization and Performance

Abstract

Perovskite solar cells (PSCs) have rapidly achieved power conversion efficiencies (PCEs) comparable to crystalline silicon over the past decade, offering a promising low-cost alternative. However, commercialization remains hindered by the reliance on lab-scale fabrication methods and the use of toxic solvents, which pose environmental and health concerns. Atmospheric-pressure spatial atomic layer deposition (AP-SALD) represents a scalable, solvent-free approach for fabricating charge transport layers, and when combined with green-solvent-processed perovskites, offers a sustainable pathway for large-scale PSC production. Despite this potential, tin oxide (SnOX) electron transport layers deposited via AP-SALD (SALD SnOX) have historically underperformed compared to their nanoparticle-based counterparts (NP SnOX). This study investigates the root causes of this performance gap by analyzing the energetic, chemical, and morphological properties of SALD SnOX layers and their interfaces with perovskite light absorbers. Furthermore, the work explores and optimizes PSCs fabricated entirely using green-solvent and solvent-free techniques. Our findings show that post-annealing SALD SnOX at 180 ˚C significantly enhances conductivity, thereby improving key photovoltaic parameters. Additionally, we demonstrate that the conformal-coating nature of AP-SALD can amplify substrate roughness, negatively affecting perovskite crystallization—unlike spin-coating, which inherently smooths the surface. By optimizing the SALD SnOX thickness and utilizing smoother fluorine-doped tin oxide (FTO) substrates, SALD SnOX-based n-i-p PSCs achieve a PCE exceeding 20%, matching the performance of NP SnOX-based reference cells for the first time. Introducing a green-solvent-processed perovskite layer into the PSC stack initially results in reduced performance. To address this, polystyrene (PS) is incorporated into the perovskite precursor to form a cross-linked polymer–perovskite network, which improves grain nucleation and growth, leading to enhanced device performance. Notably, the SALD SnOX ETL demonstrates a positive influence on the crystallinity of the green-solvent perovskite, supporting earlier findings. Overall, this work delivers critical insights into interfacial engineering strategies for achieving scalable, environmentally friendly, and high-performance PSCs, reinforcing the viability of AP-SALD for industrial application.