# Presentation: 098127

## Thin Films and the System-Driven Approach (SDA)

**Ken Zweibel**
**Thin Film PV Partnership**
**NREL**

## What I am going to say

- Thin film modules and *systems* can be very cheap
- Module efficiency is somewhat more critical to thin films than module cost reductions, because efficiency must offset “balance of module” (BOM) and “balance of system” (BOS) costs
- However, module cost reductions are also important and can be critical
- Attempts to improve thin film module costs are hampered by stubborn packaging and design commonalities (BOM)
- Of various cost reduction strategies, reducing semiconductor deposition cost will likely form the heart of progress in module cost reduction
- Reducing packaging costs (tho perhaps ultimately more valuable) may be harder (due to reliability issues)
- Thin films that are either
- Too expensive, or
- Too inefficient
- 		are likely to be marginalized in the marketplace.
- SDA provides a framework for seeing these matters clearly and designing appropriate research to address them

## Module cost baselines and extremes

**Input data comes from spreadsheet bottom-up estimate **
**Will be published in book chapter **
**Input includes current status and predictions of cost reductions**
**Based on technical improvements and volume production**
**Back-up material includes recent HP study (NREL/SR-520-36844) of very large scale manufacturing cost savings – a poster at this meeting**
**Communications from companies (but used only in generic form)**
**Prior published information (including quarterly reports, journal articles, NREL reports and studies)**
**Website product price estimates**
**Informed guesses (inevitable and important)**
**These are direct manufacturing costs and assume reasonable steady-state at about 25 MW/yr**
**This is consistent with the purpose of discovering key research drivers**

## Reasonable (but generic) current values of capital, materials, labor, and energy input for commercial thin films

- The sweet spot today

## Costly Version

- Extremely high capital
- Extremely high semi materials
- Extremely high labor and energy
- Everything else high, too

- Cheap Version
- Everything cheap
- Cheap semis on plastic substrates and barriers
- High volume and automation

## Comments

- In terms of the low-cost extreme – this is what comes of using plastic on the front and back/substrate, a paint-on semiconductor, high-speed deposition and interconnection – this is ‘the ultimate’ thin film (and not practical yet; or maybe ever?) – it is here as one pole of possibility
- In fact, some designs that *seem* cheaper than glass may not be if they entail an extra layer of protective plastic and adhesive *in addition* to the film’s substrate
- It is NOT true that all thin films are cheap or can be competitive: BOTH cost and efficiency (and stability) are needed.

## What are the key cost elements?

- The Semiconductors – *cost reductions via research*
- Deposition costs
- Capital, maintenance, energy, footprint
- Faster depositions, simpler equipment, lower temperatures, wider substrates
- Materials costs
- Layer thickness
- Waste
- Could be brought down to very low levels ($1/m2) with thin layers made well
- Even a $1000/kg feedstock is only *about* $1/m2 if layer thickness is half a micron
- The Packaging – *cost reductions via volume and make/buy*
- Substrate
- Package/barrier, edges
- Adhesives
*Or revolutionary changes that put reliability in question*

## SDA Thought Experiment: How Low Can We Go at the System Price Level?

- Compare baseline thin films with two other options to see where reductions could be made
- Reduced semiconductor costs (material, capital, energy, maintenance, facilities, labor)
- And reduced packaging costs (all plastic barriers and substrates, no matter how impractical that seems right now)
- Compare ‘soon’ and ‘ultimately’ to take other changes into account (BOS reductions)
- Must use “system *price*” as the metric for comparison

## Assumptions

|  | Baseline modules | Lower Semi | Lower Packaging | Lower All | Area BOS | Power BOS | Margin |
| --- | --- | --- | --- | --- | --- | --- | --- |
| Near-Term | 90 $/m2 & $134/m2 | 70 $/m2
 | 74 $/m2
 | 54 $/m2
 | 80 $/m2
 | 0.5 $/Wp | 33% |
| Ultimate | 40 $/m2
& $65/m2
 | 34 $/m2
 | 29 $/m2
 | 23 $/m2
 | 25 $/m2
 | 0.2 $/Wp | 20% |

- For comparison, if one assumes a $1/Wp x-Si module at 15%
- efficiency, the resulting long-term system price is $1.7/Wp.

## Looking inside the technologies

- CdTe is most like the “low-cost baseline,” unless Te is used poorly
- CIS could be like either baseline, depending on whether In is used poorly and some possible issues with equipment costs
- A-Si could be like either, depending on whether in-line (“high”) or batch (“low”) processes are used
- Dye cells are a *potential* a “low-semi” cost option (unproven)
- Plastic cells are *potentially* a “low-semi” cost option
*No technology* is a “low packaging” option *and none may ever be*

## Risk Reminder! Barriers to cheap packaging

- Outdoor reliability with cheaper packaging
- Processing temperature limits using cheaper packaging
- So, in the graphs that follow, consider the pink “low-cost-semi” the most likely possible future option for progress and the yellow and green lines as envelopes of possibility

## Slide 12

## Near-term observations

- The high-cost baseline needs a 2% η advantage over the low-cost baseline to be equivalent at the system level
- Improving the low-cost baseline by nearly eliminating the semi costs, only provides about a 1% difference
- Improving it by reducing packaging also allows about 1% (impossible near term)
- Reducing both is worth about 2.5% (and is impossible near term)

## Implications for Near Term

- High-cost thin films are *unattractive* *unless they have a strong efficiency advantage*
- A high cost thin film probably has some sort of unusual cost problem with capital cost or materials cost
- Examples: wasting expensive feedstocks during deposition; or high capital costs from long fabrication times
- On the opposite extreme, today’s BOS costs wash out almost any advantage of a module designed specifically for low cost (e.g., batch a-Si, dye cells, plastics), unless it approaches the efficiency of the alternatives (e.g., CdTe, CIS)
- So what about long-term?

## Long-Term Comparison

- Assumes ‘best of’ levels for all inputs, including BOS
- Besides the assumptions of lower costs for packaging and semis, assumes the baseline thin films also improve significantly – to $40/m2 and $65/m2, respectively
- BOS substantially lower – which HELPS the differential based on lower module costs (makes module-cost-driven system cost differences larger in proportion) – this becomes the *optimistic* case for inexpensive thin film modules

## Slide 16

## Implications for Long Term

- The highest-cost thin film baseline will need a 1% efficiency advantage to be equivalent to the low-cost baseline
- The difference between the low-cost baseline  and
- Optimized semiconductor fabrication is worth 1.5% in efficiency
- Optimized packaging is worth 2.5%
- Both together, worth 4%
- At equal efficiency (15%) these are worth about 20 ¢/Wp (30% of system price)

## Looking inside the technologies

- CdTe (low cost baseline) on a good path, can try to reduce costs and raise efficiencies incrementally as production increases (no obvious bottlenecks – perhaps better tellurium use)
- A-Si needs higher efficiency; and if in-line process used, reduced costs from “factories of factories”
- CIS has efficiency advantage, but needs to reduce indium costs by thinner layers and better utilization
- Dye cells need to improve efficiency and demonstrate that they actually have lower costs (hidden issues?)
- Plastic cells need a breakthrough in efficiency
- All technologies could benefit from packaging redesigns, but changes could put reliability in jeopardy

## Final Caveats

- Tried to stay away from ideas and conclusions that depend too sensitively on precision of data
- Data *is not* and *probably cannot be* that precise (due to corporate secrecy and the rapidity of change)
- But *reasonable input data ranges* can still provide insights
- Must beware of ideas and conclusions that depend too much on *exactness of data or narrowness of perspective* (snapshot data – e.g., “now” or “from published data”), or lack proper technical intuition about what makes sense
- Can lead to *gross misperceptions *(this is a major reason the community does not like SDA, so must be carefully handled)
*Science is so creative* that no conclusion from fixed inputs can ever be considered eternal

## Value of This SDA

- Establishes *new research directions* that can be defended as not just whims but as *clearly important*
*Cost parameter provides new insights*
- Could lead to a **consensus** among researchers that these *paths should be seriously considered*
*E.g., thinner CIS and CdTe cells; lower cost processes; low-cost, flexible, nonconductive substrates that can double as encapsulation*
- Has already led to *shifts in funding* priorities within existing thin films, including greater awareness of the implications of unusually high costs or unusually low efficiencies
- Provides insight into firming R&D paths for 3G thin films – can low-cost packaging ever be done?
- May become an example for further refinement and expansion to other questions
- But...must always be compared against the wisdom of experience implicit in many people’s educated intuition and funding philosophy

## What I have said

- Thin film modules and *systems* can be very cheap
- Module efficiency is somewhat more critical to thin films than module cost reductions, because efficiency must offset “balance of module” (BOM) and “balance of system” (BOS) costs
- However, module cost reductions are also important and can be critical
- Attempts to improve thin film module costs are hampered by stubborn packaging and design commonalities (BOM)
- Of various cost reduction strategies, reducing semiconductor deposition cost will likely form the heart of progress in module cost reduction
- Reducing packaging costs (tho perhaps ultimately more valuable) may be harder (due to reliability issues)
- Thin films that are either
- Too expensive, or
- Too inefficient
- 		are likely to be marginalized in the marketplace.
- SDA provides a framework for seeing these matters clearly and designing appropriate research to address them