Perovskite Solar Cells: Challenges Facing Polymeric Hole Selective Materials in p-i-n Configuration

Polymeric hole-selective materials (P-HSMs) offer advantages like solution processability, tunable energy levels, and improved mechanical stability, making them suitable for large-scale and flexible substrates. Poly[bis(4-phenyl) (2,4,6-trimethylphenyl) amine] (PTAA) based p-i-n perovskite solar cells exhibit promising power conversion efficiency (PCE), but wettability, dopant, and cost challenges necessitate the development of advanced next-generation P-HSMs. To provide a clear understanding of the structural property with photovoltaic performance, this review classifies such newly developed P-HSMs into five distinct structural categories. Specifically, this review discusses the current status, advancements, challenges, and prospects in structural design and synthetic variations, focusing on enhancing photovoltaic performance, wettability, mitigating surface defects, and stability. Notably, incorporating polar units into P-HSMs enhances wettability and mitigates ion instabilities and uncoordinated lead defects. Promising structural designs like polymeric self-assembled monolayers and in situ polymerized hole-selective materials are examined. Despite performance advancements, emerging, P-HSMs face significant challenges such as limited thermal stress analysis (55-85 degrees C) and scalability restricted to small-scale devices. To bridge this gap, this review emphasizes the urgent need for prioritizing thermal stability testing and large-scale device fabrication in future research, paving the way for commercial viability of P-HSMs in p-i-n perovskite photovoltaics.