Molecular Engineering of Highly-Stable High-Performance Lead-Free Perovskite Solar Cells
Abstract
Halide perovskites are a new type of semiconductor that show great promise in optoelectronic devices. Tremendous progresses have been made in achieving highly efficient thin film solar cells. Using the lead-based perovskites such as (CH3NH3)PbI3 as the solar absorber, certified power conversion efficiency of 23.3% has been demonstrated. The poor stability of the perovskite materials, as well as the use of toxic elements (Pb), are the major concerns for real application of this new type of solar cell. As a promising alternative, Sn (II)-based perovskites exhibit smaller optical band gap, comparable or even better charge carrier mobilities and lifetimes. Unfortunately, the stability of the Sn (II)-based perovskites is even worse than the Pb-based perovskites due to oxidation and hydrolysis reactions with oxygen and moisture. To address this issue, studies on alloying Pb with Sn have been carried out. Although the stability can be improved using 30% ~ 50% Pb, the overall performance decreased due to high defect density and poor film morphology. Moreover, the toxicity problem is not solved by making Pb-Sn alloy with a high Pb content. Recently, it has been shown that by inserting larger organic cations into the perovskite slabs, the 2D perovskites exhibit slightly improved stability. Nevertheless, the organic parts are usually electronically-inactive and they block charge transportation between the perovskite layers. As a result, the performance of the devices is low. On the other hand, semiconducting organic materials that facilitate charge transport can be inserted into halide perovskites, but the chemistry of making such complex structures is rather difficult. Here, we propose to apply organic chemistry principles to design conjugated molecular cations and use them for molecularly engineered 2D and quasi-2D hybrid perovskites containing Sn2+ instead of Pb2+. We hypothesize that the organic building blocks are essential to tune the band structure, charge carrier dynamics, and transport properties; and more importantly, to stabilize the Sn (II)-based halide perovskites. Using the organically functionalized Sn perovskites, high-performance solar cells with low toxicity will be fabricated and investigated.The proposed research is transformative and significant because it will enhance our fundamental understanding of organic-inorganic hybrid materials and interfaces; and accelerate the discovery of better hybrid semiconductor materials for solar cells as well as other defense-related applications, such as near-IR photodetectors and solid-state lightings.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Apr 25, 2019
- Source ID
- N000141912296
Entities
People
- Letian Dou
Organizations
- Office of Naval Research
- United States Navy
- University of Virginia