Dr Dongtao Liu

Enormous progress has been made in formamidinium tin triiodide (FASnI3)-based inverted perovskite solar cells (IPSCs). However, the instability issue remains a significant obstacle in both the fabrication and evaluation of the entire device. According to the lessons learned from lead-based PSCs, stability is difficult to address compared to other performance metrics during the optimization process. Therefore, it is imperative to explore the sources of instability and the underlying pathways of device degradation, especially in PSCs incorporating sensitive Sn2+. This review begins by introducing the prevalent light absorber and device structure in lead-free Sn-based IPSCs. The rationale behind the widespread utilization of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) in Sn-based PSCs is thoroughly examined. Then, the principal degradation mechanisms and potential reactions are assessed under different stress conditions. Based on the International Summit on Organic Photovoltaic Stability protocols, recent strategies for improving device stability are systematically summarized, including the engineering of solvents, components, additives, and passivation on perovskite or PEDOT:PSS. The final section offers insights into addressing current challenges and provides perspectives about the future development of stable Sn-based IPSCs.

Metal oxide charge transport materials are preferable for realizing long-term stable and potentially low-cost perovskite solar cells (PSCs). However, due to some technical difficulties (e.g., intricate fabrication protocols, high-temperature heating process, incompatible solvents, etc.), it is still challenging to achieve efficient and reliable all-metal-oxide-based devices. Here, we developed efficient inverted PSCs (IPSCs) based on solution-processed nickel oxide (NiOx) and tin oxide (SnO2) nanoparticles, working as hole and electron transport materials respectively, enabling a fast and balanced charge transfer for photogenerated charge carriers. Through further understanding and optimizing the perovskite/metal oxide interfaces, we have realized an outstanding power conversion efficiency (PCE) of 23.5% (the bandgap of the perovskite is 1.62 eV), which is the highest efficiency among IPSCs based on all-metal-oxide charge transport materials. Thanks to these stable metal oxides and improved interface properties, ambient stability (retaining 95% of initial PCE after 1 month), thermal stability (retaining 80% of initial PCE after 2 weeks) and light stability (retaining 90% of initial PCE after 1000 hours aging) of resultant devices are enhanced significantly. In addition, owing to the low-temperature fabrication procedures of the entire device, we have obtained a PCE of over 21% for flexible IPSCs with enhanced operational stability.

Halide perovskites are a compelling candidate for the next generation of clean-energy-harvesting technologies owing to their low cost, facile fabrication and outstanding semiconductor properties. However, photovoltaic device efficiencies are still below practical limits and long-term stability challenges hinder their practical application. Current evidence suggests that strain in halide perovskites is a key factor in dictating device efficiency and stability. Here we outline the fundamentals of strain within halide perovskites relevant to photovoltaic applications and rationalize approaches to characterize the phenomenon. We examine recent breakthroughs in eliminating the adverse impacts of strain, enhancing both device efficiencies and operational stabilities. Finally, we discuss further challenges and outline future research directions for placing stress and strain studies at the forefront of halide perovskite research. An extensive understanding of strain in halide perovskites is needed, which would allow effective strain management and drive further enhancements in efficiencies and stabilities of perovskite photovoltaics.