Materials and Interface Engineering for Highly Efficient and Stable 2D/3D Tin Pseudohalide Perovskite Solar Cells

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Photovoltaic (PV) technology is sustainable, clean source of energy with the capacity to fulfill our growing energy needs. Hybrid organic-inorganic lead halide perovskite solar cells (PSCs) have emerged in the past decade as a promising low-cost, thin film solar cell with high efficiency and roll-to-roll printing processability, which could encourage a transition into a clean energy economy. However, the use of lead raises the concerns for commercialization because of the potential environmental contamination and human health problems. It is important to carefully find an environmentally benign and efficient replacement for lead with a focus on keeping the excellent properties ascribed to its presence in perovskite materials. Tin perovskite is regarded as an ideal candidate to replace lead perovskite with the theoretical PCE of tin PSCs close to 30% according to Shockley-Queisser limit. Despite progress having been made, the efficiency and stability of tin PSCs are still inferior to their lead counterparts. This project will apply a synergetic approach via materials and interface engineering with the goal to reduce defects, suppress tin oxidization, enhance charge extraction and transport, and reduce energy losses, hence, to increase the efficiency and stability of tin PSCs. Success in this project will advance the knowledge of ionic semiconducting materials and device physics of thin film solar cells, which could lead to a transition into a clean energy economy because of potential commercialization of lead-free, highly efficient and stable PSCs fabricated with low-temperature, large-area, high-throughput processes. Graduate and undergraduate students from underrepresented groups will receive training in this highly interdisciplinary research project. The knowledge gained from this work will be disseminated through the workshop that the PI group will offer to the annual event of Expanding Your Horizons at Cornell campus and Ithaca Sciencenter by providing hands-on activities and demonstrations for young students and their families. The challenge with tin-based PSCs is primarily due to tin-defects, resulting in the undesirable nonradiative recombination of photocarriers and metallic conductivity, and the attendant loss of open-circuit voltage. Additionally, the dangling bonds on the surface and at the grain boundaries introduce trap states, which act as the centers of nonradiative recombination and degradation sites. The research team aims to (1) develop novel Dion-Jacobson (DJ) phase two-dimensional and three-dimensional (2D/3D) tin pseudohalide perovskites to reduce tin defects and passivate defects at the grain boundaries and surfaces; (2) synthesize new hole transport materials by introducing functional groups to guide perovskite growth and reduce interface trap states; and (3) deploy new hole and electron transport materials in tin PSCs to increase device efficiency and stability. Forming DJ phase 2D/3D hybrid tin perovskites represents a paradigm shift in tackling the challenge of efficiency and stability of tin-based PSCs. The intellectual merit is driven by our hypotheses: (1) the defects can be significantly reduced and the tin oxidation can be effectively suppressed by adopting large A’-site divalent cations and pseudohalide anions to form 2D/3D bulk and planar heterojunction tin perovskites; and (2) the energy losses can be significantly reduced and the device stability can be greatly enhanced by utilizing newly developed hole and electron transport materials to guide perovskite growth and passivate defects, respectively. By fundamentally understanding the structural and optoelectronic properties of DJ phase 2D/3D tin pseudohalide perovskites, the effect of functionalized hole transport layer on the growth of perovskites, and the non-fullerene acceptor interaction with perovskites, the general principles to guide the development of highly efficient, stable tin PSCs can be elucidated, which could lead to the transformation of clean energy techniques. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.