TECHNOLOGY AREA(S): Sensors
OBJECTIVE: Design, fabricate, and demonstrate flexible perovskite solar modules (12"x12") providing efficiency greater than 20% under AM 1.5G standard solar spectrum with stability under up to 50°C of temperature and up to 80% of humidity. Demonstrate the modules for direct powering of wireless sensor nodes and battery recharging operation for wearable electronics relevant to defense platforms.
DESCRIPTION: Wireless sensor nodes are becoming ubiquitous in the battlefield environment for the detection of chemical and biological agents, acoustic waves, etc. as well as for electronic health monitoring and tracking inventory of remotely deployed weapons systems. However, the finite capacity of exiting energy sources has become a major limitation in deploying them for unattended operations for a long duration. Therefore, it has led to an increasing demand for harvesting energy from the environment. However, diffused light spectrum is the only environmental energy source available for efficiently powering the nodes. Diffused light becomes a promising source in this case for powering the sensors and transferring the data to a workstation. Furthermore, field infantry electronics such as radios, GPS, night vision systems, and fire light require soldiers to carry a lot of spare batteries in addition to the body armor, weapons, food, and water. A tremendous impact on the total load can be made if a soldier uniform can be designed to harvest the freely available energy from the environment such as solar energy to continuously recharge the main battery. Although foldable solar blankets currently used in the battlefield provide the capability to charge the batteries under sunlight, they often take hours to collect enough power for charging. The current market for photovoltaic devices is dominated by crystalline silicon solar panels with typical efficiencies of ~15 - 20%, and the fragile properties of silicon solar panels limit their application on wearables and complex curved surfaces, especially in diffused low light conditions such as in cloudy weather. Flexible solar modules based upon amorphous Si (a-Si), CuInxGa1-xSe2 (CIGS), and GaAs materials are commercially available, but with limited efficiencies (~10 - 15%). The complex growth conditions of these materials not only lead to high cost but also present a significant challenge in their large-scale production. Furthermore, slight increase in temperature also tends to reduce the bandgap of the semiconductor materials leading to significant degradation of performance. Therefore, the flexible photovoltaics needed for the defense platforms that meet the deployment and operational requirements demand new technologies. The emergence of organometal perovskite solar cells (OPSC) fabricated by solution-casting light absorbers has provided the opportunity for the development of low cost and high performance flexible modules. The typical structure for OPSC is similar to a p-i-n heterojunction solar cell with several unique features: (i) Small bandgap and large light absorption coefficient yields large amount of photo-generated electrons and holes. (ii) Short light absorption length (~200 nm) requires only very thin layers of perovskite for light harvesting. (iii) High electron-hole mobility and large electron-hole diffusion lengths make them excellent candidates for photovoltaic applications. (iv) The low-temperature solution-based processes to prepare the perovskite allow the integration with flexible plastic substrates and other photovoltaic devices. At present only limited results have been reported in the literature on performance of perovskite solar modules. All studies have focused on small lab-scale (~0.1 cm2) prototypes. Translating the lab-scale perovskite solar cells into low-cost large-scale production process is one of the major challenges in the development of perovskite solar modules. Therefore, the objective is to address this technology gap in the design and fabrication of perovskite photovoltaic modules for the intended integration. Flexible modules may need to incorporate re-designed cell architecture to make them compatible with the synthesis process required for the flexible substrates (eg. 3D printing processes). Printing and casting processes may need to be developed for perovskites to allow layering with precise dimensions and desired interfacial characteristics. Investigations may also need to be conducted on multiple compositions under various environmental conditions to determine the optimum window for the module operation relevant to the wireless sensors and wearable electronics applications. Field testing may also need to be conducted to determine the failure and aging mechanisms of the modules, and strategies should be proposed to resolve the environmental degradation issues.
PHASE I: Complete the design of the architecture for a flexible perovskite module with an efficiency greater than 20% for wearable energy harvesting and wireless sensor nodes application and develop the fabrication procedures. Designs should include realistic material parameters. The flexible photovoltaic fabrication technique should be based on a low-temperature process. Analyze cost-competitive roll-to-roll printing process for mass fabrication of the flexible photovoltaic module. Provide preliminary experimental results on the feasibility of the proposed module architecture including bandgap-voltage offsets.
PHASE II: Develop a low-cost inorganic p-type semiconductor to replace the spiro-OMeTAD and integrate with the module architecture developed in Phase I. Address the hysteresis, thermal and humidity challenges and demonstrate a method to improve the lifetime. In addition to the heterojunction-induced built-in electric field as driving force to separate and transport the photo-excited electron-hole pairs, demonstrate the role of other effects in improving the efficiency. Demonstrate the wireless sensor node operation utilizing adequate size modules for a specific targeted defense application. Integrate the fabricated module up to 12 x12 area with a wearable and demonstrate the battery recharging capability under normal environmental conditions.
PHASE III: Demonstrate continuous roll-to-roll manufacturing of the developed modules and integration with the wearables and sensor nodes. Optimize the power conversion efficiency for flexible perovskite solar modules, the module geometries (such as stripe width, gap size, module length), and stability under various environmental conditions and strain. Develop packaging layers to provide adequate protection over the intended lifetime of the application. Focus should be on integrated product development and not on just the power source.
1: Dong, Y. Fang, Y. Shao, P. Mulligan, J. Qiu, L. Cao, and J. Huang, Science, Vol. 347, pp. 967-970 (2015).
2: W. Chen, Y. Wu, Y. Yue, J. Liu, W. Zhang, X. Yang, H. Chen, E. Bi, I. Ashraful, M. Grtzel, and L. Han, Science, Vol. 350, 944-950 (2015).
3: M. Yang, Y. Zhou, Y. Zeng, C.-S. Jiang, N.P. Padture, and K. Zhu, Adv. Mater., Vol. 27, 6363-6070 (2015).
4: X. Zheng, B. Chen, C. Wu, and S. Priya, Nano Energy, 17, 269-278 (2015).
KEYWORDS: Energy Harvesting, Wireless Sensor Nodes, Perovskite Solar Module