N21A-T009 TITLE: Organic Solar Cell Processing and Product Development
RT&L FOCUS AREA(S): Autonomy; General Warfighting Requirements
TECHNOLOGY AREA(S): Materials / Processes
OBJECTIVE: Develop and demonstrate, on increasing scales, solar cell designs and manufacturing processes for production of low cost, lightweight, and flexible organic solar cells with power conversions efficiencies greater than 13%. Materials in the solar cell stack should have inherent stability (i.e., photo, chemical (air and moisture), morphological, mechanical) to enable a reasonable lifetime with lightweight packaging. Solar cell packaging should support applications on fabric and enable associated folding/rolling without cell damage.
DESCRIPTION: Solar power is an integral part of forward operations, especially those relevant to future Expeditionary Advanced Base Operations (EABO), where austerity requires a high-performance, lightweight solution. Currently, the USMC uses Copper Indium Gallium Diselenide (CIGS) thin film cells that do not meet the rated power conversion efficiency (PCE) or durability. Single junction organic solar research cells have achieved PCE of 16% using conjugated polymer donors and non-fullerene acceptors bulk heterojunction materials with the promise of even higher performance [Ref 1]. While still below silicon, the promise of roll-to-roll manufacturing on flexible substrates with intrinsic stability enables minimal packaging and more versatile applications beyond the rigid (rooftop) market that silicon dominates. For the domestic market there are opportunities for opaque, colored, or semitransparent architectural solar films. For the military, durable and foldable laminates on tarps, tents, and backpacks that do not add weight are highly desired.
Existing organic solar cell commercial products were developed based on prior generation polymer/fullerene bulk heterojunction systems that peaked with research cell efficiencies of 10% for single junction and higher for multijunction. These have not established a stable market, but it is likely the higher performance materials can do this, especially for the market niches described above. However, academic research has focused on high overall power conversion efficiencies and not on product development efforts. Solar cell developers will need to pay attention to material issues associated with attaining desirable and stable bulk heterojunction morphologies, in addition to the series resistance and packaging issues associated with going from a research cell toward a practical module [Ref 2]. Past development efforts have pursued manufacturing using both vacuum deposition and roll-to-roll printing processes. Either approach is acceptable here so long as a realistic and defensible cost model is presented for the military/recreational applications identified above.
The proposed STTR team should already have demonstrated ability to produce research cells with verified overall power conversion efficiency of 13% or higher and should present and explain the selection of all the materials in their device stack (for performance, stability, processing) that could be scaled with cost-effective processing. The goal of Phase I is to move from a research cell to depositing multiple 1 square centimeter cells using processing approaches that will be scaled in Phase II. This can be done on rigid or flexible substrates. The cells should show power conversion efficiencies of 13% with less than 10% performance loss to break-in over 100 hours unpackaged and 1000 hours packaged. The deliverable for Phase I will be a device that meets those specifications and can be made available to third party testers.
PHASE I: Develop processing approaches for depositing multiple 1 square centimeter cells on either rigid or flexible substrates connecting them in series to form a module. Ensure that the cells show power conversion efficiencies of 13% with less than 10% performance loss to break-in over 100 hours unpackaged and 1000 hours packaged. Characterize module level performance and series resistance. Produce a final report that includes plans for a 50 square centimeter module on non-rigid substrate with modeled performance, the processing and packaging approach for this module and larger modules, and an updated cost analysis. Develop a Phase II plan.
PHASE II: Develop and process a 50 square centimeter module on a flexible substrate, targeting >11% overall power conversion efficiency, flexible packaging, and packaged lifetimes of 5-10 years. Fully test the stability of rigid and flexible cells and mini-modules. Study the mechanical stability of the mini-modules. Push processing to larger modules. Ensure that the prototype is available for validation. Develop product concepts for military and recreational applications. Update cost analysis for appropriate markets. Seek partnerships for product development.
PHASE III DUAL USE APPLICATIONS: Scaling of device fabrication to cost effective processes. Develop larger modules targeting specific products. Work with DoD and partners towards maturing products. DoD and commercial products would be solar cells that can be applied to tents and backpacks without adding substantial weight, could survive the normal uses of these products, and realize performance and lifetime detailed in this topic description.
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KEYWORDS: Organic solar cells; flexible solar cells; non-fullerene acceptors; low cost; lightweight; robust; Copper Indium Gallium Diselenide; CISG