New Pathway Emerges To Improve Polycrystalline Thin-Film Solar Cell Performance
Puzzling out and testing new ways to improve the efficiency of cadmium telluride (CdTe) polycrystalline thin-film photovoltaic materials is a typical day in the life of National Renewable Energy Laboratory (NREL) research scientists Matthew Reese and Craig Perkins. Like any good puzzlers, they bring curiosity and keen observation to the task. These skills led them, over time, to make an intriguing observation. In fact, their discovery may prove to be a boon for the next generation of several different types of thin-film solar cells.
When fragments of solar cell material are crystallized together, or “grown” — think of a piece of rock candy growing in layers in a cup of sugar — they create a polycrystalline solar cell. With many layers come many surfaces, where one layer ends and another begins. These surfaces can cause defects that restrict the freedom of electrons to move, reducing the cell’s efficiency. As the cells are grown, researchers can introduce specific compounds that minimize the loss of electrons at these defects, in a process called “passivation.”
Reese, Perkins, and Colorado School of Mines doctoral student Deborah McGott noticed that the three-dimensional (3D) CdTe solar cells’ surfaces appeared to be covered in a very thin, two-dimensional (2D) layer that naturally eliminated surface defects. This 2D passivation layer forms in sheets on the 3D light-absorbing layer as the cell is growing, in a standard processing technique that is used around the globe. Despite the ubiquity of this 2D passivation layer, it had not been observed or reported in the research literature. Reese, Perkins, and McGott believed 2D passivation was also occurring naturally in other thin-film solar cells, like copper indium gallium selenide (CIGS) and perovskite solar cells (PSCs). They realized that this observation could lead to the development of new methods to improve the performance of many types of polycrystalline thin-film cells.
To confirm their hypothesis, they discussed it with NREL colleagues in the CdTe, CIGS, and PSC research groups. Through many informal discussions involving coffee, hallway chats, and impromptu meetings, Reese, Perkins, and McGott arrived at an “aha” moment. Their CdTe and CIGS colleagues confirmed that, while their research communities were not generally trying to perform 2D surface passivation in the 3D light-absorbing layer, it was, in fact, occurring. The PSC researchers said that they had noticed a 3D/2D passivation effect and were beginning to intentionally include compounds in device processing to improve performance. The “aha” moment took on even more significance.
“One of the unique things about NREL is that we have large groups of experts with different pools of knowledge working on CdTe, CIGS, and PSC technologies,” Reese said. “And we talk to each other! Confirming our hypothesis about naturally occurring 3D/2D passivation with our colleagues was easy because we share the successes and setbacks of our diverse research in an ongoing, informal, and collaborative way. We learn from each other. It is not something that typically happens in academic or for-profit-based polycrystalline thin-film solar cell research, where information is closely held, and researchers tend to remain siloed in their specific technology.”
The details of Reese, Perkins, and McGott’s discovery are presented in the article “3D/2D passivation as a secret to success for polycrystalline thin-film solar cells,” published in the journal Joule.
Supporting Evidence in the Literature
To confirm their findings, McGott conducted an extensive literature search and found considerable supporting evidence. The literature confirmed the presence of passivating 2D compounds in each of the CdTe, CIGS, and PSC technologies. No mention was made, however, of the 2D compounds’ ability to improve device performance in CdTe and CIGS technologies. While many articles on PSC technologies noted the naturally occurring 3D/2D passivation effect and discussed efforts to intentionally include specific compounds in device processing, none suggested that this effect might be active in other polycrystalline thin-film photovoltaic technologies.
Polycrystalline thin-film solar cells are made by depositing thin layers, or a thin film, of photovoltaic material on a backing of glass, plastic, or metal. Thin-film solar cells are inexpensive, and many people are familiar with their more unique applications. They can be mounted on curved surfaces — to power consumer goods, for example — or laminated on window glass to produce electricity while letting light through. The largest market for thin-film solar cell applications, however, is for CdTe thin film on rigid glass to make solar modules. CdTe modules are deployed at utility scale, where they compete directly with conventional silicon solar modules. Currently, commercial thin-film modules are generally less efficient than the best single crystal silicon solar modules, making performance improvements a high priority for polycrystalline thin-film researchers.
Key Properties of 2D Materials
Reese, Perkins, and McGott’s team used surface science techniques combined with crystal growth experiments to show that the 2D layers existed at and passivated 3D absorber surfaces in the three leading polycrystalline thin-film photovoltaic technologies. They then analyzed the key properties of successful 2D materials and developed a set of principles for selecting passivating compounds.
Finally, the team outlined key design strategies that will allow 3D/2D passivation to be employed in polycrystalline thin-film photovoltaic technologies more generally. This is particularly important because each 3D material requires a specific passivation approach.
The literature results, combined with lab-based observations, show that 3D/2D passivation may be the secret to success in enabling next-generation thin-film solar cells, particularly if researchers freely share the knowledge developed for each technology. The lack of 3D/2D passivation may even shed light on the stalled performance improvements of some polycrystalline technologies such gallium arsenide. By drawing parallels between the three technologies, Reese, Perkins, and McGott hope to demonstrate how the knowledge developed in each can — and should — be leveraged by other technologies, an approach that is seldom seen in polycrystalline thin-film solar cell research.
CdTe, CIGS, and PSC thin-film research at NREL is funded by the Department of Energy’s Solar Energy Technologies Office. Additional funding for Reese and McGott’s research is provided by the Department of Defense’s Office of Naval Research.
Learn more about photovoltaic research at NREL.
Article courtesy of the NREL, The U.S. Department of Energy.
This week on Electrek’s Wheel-E podcast, we discuss the most popular news stories from the world of electric bikes and other nontraditional electric vehicles. This time, that includes the potential end of Rad Power Bikes, Tern’s new belt-drive Vektron, a semi-solid-state e-bike battery coming soon on a production e-bike, ALSO drops price on its entry-level model, a tilting flat-bed electric trike/truck, and more.
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For most of human history, currency was a direct claim on tangible, productive output. Before the abstraction of government fiat or cryptocurrency, value was stored in things that required real work and resources, bushels of grain, livestock, gold, assets with their own direct productive output: horses, and tragically, slaves.
These were the foundational assets of economies, representing a direct link between labor, resources, and stored value.
As we accelerate into an all-electric, all-digital age, this fundamental link is re-emerging, but with a new unit of account. The 21st-century economy, defined by automated industry, robotic, electric transport, and now power-hungry artificial intelligence, runs on a single, non-negotiable input: electricity. In this new paradigm, the real base currency, the ultimate representation of productive capacity, is the kilowatt-hour (kWh).
The kWh is the new economic base layer.
Last week, I was in Bijiashan Park at night overlooking Shenzhen, arguably the most technologically advanced city on earth, built over the previous few decades, partly on cheap electricity, cheap labor, and manufacturing innovations.
I could see the giant high-voltage power lines coming over Yinhu Mountain to power the constant light show that is Shenzhen at night. I couldn’t help but think about how cheap electricity and a strong grid have been critical to China’s exceptional economic rise.
As you stroll around the city, you see power everywhere. There are charging stations at every corner, including insane 1 MW charging posts, electric cars and trucks, trucks that carry batteries to electric scooter shops, which are also literally everywhere.
Everything moves on electric power. Industries are powered by electricity, and now, with the advent of AI, virtually everything is increasingly processed by LLMs, which are ultimately powered by electricity through power-hungry data centers.
In a world where everything runs on electricity, electricity itself becomes the currency of civilization.
It is measurable, divisible, storable, and universal – all qualities that a currency needs, but unlike fiat and crypto, it’s actually directly linked to productive output. No politics. No inflation. Just physics.
This concept is not merely academic; it appears to be the quiet, guiding principle in China. While others debate the merits of decentralized digital tokens, China is executing a multi-pronged strategy that treats electricity as the foundational strategic asset it has become.
First, China is building the “mint” for this new currency at an incredible, world-changing scale, and it has retained absolute state control over its distribution. Its deployment of new electricity generation, particularly from renewables, is staggering. The country met its 2030 target of 1,200 gigawatts of renewable capacity five years early, in 2025.
In 2024 alone, renewable energy accounted for a record 56% of the nation’s total installed capacity, with clean generation meeting 84% of all new demand.
Here’s a comparison of electricity generation between China and the US:
If this chart doesn’t scare the West. I don’t know what will. The trend is not reversing any time soon. In fact, it appears to be accelerating as China is doubling down on solar and nuclear.
State-owned monoliths manage this entire system, primarily the State Grid Corporation of China (SGCC), the world’s largest utility. For better or worse, this centralized control allows the state to execute massive national strategies impossible in a liberalized market, such as building an Ultra-High-Voltage (UHV) grid to transmit power from remote solar and wind farms in the west to the power-hungry industrial hubs on its coast.
Second, China wields its control over the grid as a precision tool of industrial policy. China’s average electricity rate of $0.084/kWh is cheaper than most of the rest of the world, but its power lies not in the base price but in its strategic application. The government deploys a “Differential Electricity Pricing” policy: a “stick” that penalizes low-tech, high-consumption industries with higher rates, and a “carrot” that provides preferential pricing to incentivize strategic sectors.
The most potent example is in the AI sector. China is now offering massive electricity subsidies, cutting power bills by up to half, for data centers run by giants like Alibaba and Tencent. The condition for this cheap power is that these companies must use locally-made, Chinese AI chips, such as those from Huawei.
China is spending its “electricity currency” to directly fund the growth of its domestic AI chip industry and sever its dependence on foreign technology. This same logic applies to its global dominance in green tech, where state-subsidized firms like BYD benefit from a state-controlled industrial ecosystem built on reliable, managed power.
Third, and possibly the most explicit exemplification of China viewing electricity as the base currency is its moves against cryptocurrency.
In 2021, the government banned all cryptocurrency transactions and mining. While the official reasons cited financial stability, the move might have had a deeper, strategic intention.
From the state’s perspective, it was a tool for capital flight, allowing wealth to bypass government controls. But in a world where electricity rules, cryptocurrencies are, in effect, a competing “currency” that burns the foundational asset (electricity) to create a decentralized store of value.
By banning crypto, China simultaneously reclaimed its monopoly on economic control and shut down a massive, “wasteful” leak of its most precious resource. It freed up that generating capacity to be strategically allocated to its preferred industries, like AI and manufacturing.
China’s actions, viewed together, are a clear and coherent strategy. By massively investing in and securing total state control over its domestic electricity supply (the “mint”), using its price as a tool to fuel strategic industries, and banning decentralized competitors that consume the same resource, China is making a clear bet. It has been recognized that in an age where all productivity is powered by the grid, the ultimate source of national power is not gold, fiat, or crypto, but the state-controlled kilowatt-hour.
The Blockchain and Crypto: Ledger vs. Furnace
This perspective brings a critical nuance to the role of blockchain technology. In an economy where electricity is the base currency, the blockchain makes perfect sense, but only as a ledger, not as a store of value.
A distributed ledger is the ideal technological layer to act as the accounting system for this new economy. It can track the generation, transmission, and consumption of every kilowatt-hour with perfect transparency. It can automate complex industrial contracts and manage the grid’s load balancing without a central intermediary. In this sense, blockchain is the “banking software” for the electricity standard.
However, “Proof of Work” cryptocurrencies like Bitcoin face a fatal contradiction within this paradigm. They aim to serve as a store of value by burning the base currency (electricity) to secure the network. If the kilowatt-hour is the 21st-century equivalent of gold, then Bitcoin mining is akin to melting down gold bars to print a paper receipt. It destroys the productive asset to create a derivative token.
Bitcoin is quickly losing credibility as a classical safe store of value. It trades like a security, at least over the last year, and its value is only whatever the next moron is willing to pay, with no valuable asset behind it.
China’s strategy reflects this precise understanding. While they ruthlessly banned Bitcoin mining (the “furnace” that wastes the asset), they have simultaneously championed the Blockchain-based Service Network (BSN) and the Digital Yuan. They have embraced the ledger to track and control their energy economy, while rejecting the supposed asset that destroys it.
This is a trap that crypto fans often fall into. They recognize the value of the blockchain, which is real, but they mistakenly broadly assign the same value to cryptocurrency, which is simply an application of the blockchain.
Electrek’s Take
What I’m trying to explore in this op-ed is the idea that if the present is electric and the future is even more electric, then it makes sense for electricity to be the foundation of the economy.
If electricity is the backbone of global trade and the metric of productivity, the kWh ultimately becomes the real currency of a truly electrified world.
And I think China has figured this out, as evidenced by its new electricity generation surpassing the rest of the world combined and by its ban on cryptocurrency.
They are going to let the rest of the world hold the crypto bag while they have more electricity generation than anyone to power their industries, which are already taking over the world.
I think the rest of the world should learn from this. Instead of pouring capital into meme coins and made-up stores of value, we should invest in electricity generation and storage.
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