World Tech Rankings
China in critical technologies

Is China winning the clean energy research race?

Yes. China writes the largest share of the world's most influential research in batteries, supercapacitors, hydrogen by electrolysis and perovskite solar cells. Its share of supercapacitor research is falling as India's rises.

Measured by each country's share of the 10% most cited clean energy research papers published 2021–2025, as of October 2026. It counts research influence, not total output, products or industry. How it's measured

Year by year, China is pulling ahead

Each line shows how much of a year's most influential research came from each country.

ChinaUnited StatesOther leadersHover or tap a year. Open a chart for the full ranking.

Electric batteries2021–2025 overall: China 68.0%, US 7.6%
04080% 20052010201520202025 CN 71.8%US 5.5%
Supercapacitors2021–2025 overall: China 46.3%, US 2.3%
03060% 20052010201520202025 CN 39.1%IN 17.2%US 2.2%
Hydrogen by electrolysis2021–2025 overall: China 53.0%, US 4.4%
03060% 20052010201520202025 CN 58.7%US 4.3%
Perovskite solar cells2021–2025 overall: China 53.9%, US 6.5%
04080% 20052010201520202025 CN 62.5%US 3.8%

Share of each year's 10% most cited papers, with each paper's credit split between its authors' countries. Source: OpenAlex, pulled 24 October 2026.

Table of the numbers
Electric batteries: share of the 10% most cited papers by year
YearChinaUnited StatesTop papers
200518.1%16.7%41
200623.6%28.0%48
200728.9%15.2%54
200826.0%12.5%62
200919.1%32.9%65
201030.0%29.6%95
201124.7%35.5%147
201225.8%37.1%218
201326.6%28.7%316
201436.4%27.4%397
201538.3%24.9%458
201638.1%24.4%513
201744.5%24.9%602
201850.4%21.0%734
201953.8%17.2%843
202053.2%15.3%961
202159.0%12.5%1,070
202263.8%8.8%1,246
202368.0%8.1%1,376
202472.3%5.9%1,728
202571.8%5.5%2,049
Supercapacitors: share of the 10% most cited papers by year
YearChinaUnited StatesTop papers
20059.3%6.0%21
200624.0%24.7%25
200717.4%21.2%28
200819.7%28.3%33
200939.8%24.9%38
201032.0%28.3%57
201133.5%23.8%83
201240.3%19.4%119
201354.1%14.5%177
201451.7%14.6%228
201551.2%9.7%263
201649.9%11.6%311
201754.5%11.5%372
201858.9%7.5%424
201958.8%6.1%478
202053.4%6.4%493
202156.5%3.8%510
202253.1%1.8%546
202344.2%2.4%577
202442.0%1.4%646
202539.1%2.2%670
Hydrogen by electrolysis: share of the 10% most cited papers by year
YearChinaUnited StatesTop papers
20134.8%30.9%21
20148.8%33.4%26
201526.6%18.7%33
201622.4%32.7%43
201746.3%9.9%51
201852.0%9.5%67
201934.9%10.7%86
202046.1%7.6%121
202143.8%4.7%158
202246.4%4.5%207
202347.2%4.1%283
202456.7%4.5%400
202558.7%4.3%523
Perovskite solar cells: share of the 10% most cited papers by year
YearChinaUnited StatesTop papers
20146.4%39.3%31
201512.7%22.5%78
201616.0%21.0%135
201726.3%20.8%174
201839.6%17.3%219
201938.7%15.8%249
202041.4%12.3%265
202142.7%9.8%304
202251.8%8.7%316
202353.9%5.7%351
202454.7%6.1%407
202562.5%3.8%440

What stands out

  1. In 11 years, China went from behind the United States to the lead in perovskite solar cells. In 2014, China wrote about one in 15 of the most influential perovskite solar-cell papers and the United States about two in five. In 2025, China wrote about three in five and the United States fewer than one in twenty (3.8%).
  2. In supercapacitors, India is second. India writes about one in seven of the most influential supercapacitor papers (13.9%), well ahead of the United States, which is 6th with 2.3%. China writes about half.
  3. In batteries, China's lead is overwhelming. China writes about two-thirds of the most influential battery papers, about nine times the next country, the United States.

Editor's notes, re-checked against the data on every update (latest 24 October 2026); a note the data stops supporting is removed.

China gained ground in three of four areas

The United States lost ground in three. Hollow dots: 2021–2023. Filled: 2024–2025. On the right, China's change in percentage points.

2021–20232024–2025Share of the 10% most cited papers

Electric batteries
+8.0 pts
Supercapacitors
−10.5 pts
Hydrogen by electrolysis
+11.7 pts
Perovskite solar cells
+9.1 pts
The numbers behind the chart
TechnologyChinaUnited StatesNext country
Electric batteries64.0% → 72.0%9.6% → 5.7%South Korea 3.5% → 3.3%
Supercapacitors51.0% → 40.5%2.6% → 1.8%India 12.1% → 16.2%
Hydrogen by electrolysis46.1% → 57.8%4.4% → 4.4%Australia 4.4% → 3.5%
Perovskite solar cells49.7% → 58.8%8.0% → 4.9%South Korea 4.8% → 4.4%

Electric batteries: China leads by a wide margin

Rechargeable batteries: lithium-ion and the chemistries competing to replace it.

China writes about two-thirds of the most influential battery papers, about nine times the United States' share. Since 2021–2023, China's share edged up and the US share nearly halved.

2021–2025: China 68.0% (1st, about 5,080 of the 7,469 top papers), the United States 7.6% (2nd, about 570), South Korea 3.4% (3rd), the United Kingdom 2.2% (joint 4th), Germany 2.2% (joint 4th). 2021–2023 to 2024–2025: China 64.0% to 72.0%, the United States 9.6% to 5.7%. All 89 countries and institutions

Top 1%
China leads, 57.7%
Leading Chinese institution
Central South University, 1st in the world
China's most cited study
High‐Energy Lithium‐Ion Batteries: Recent Progress and a Promising Future in Applications 1,201 citations

Supercapacitors: China leads by a wide margin, India is second

Energy storage that charges and discharges far faster than a battery.

China writes about half of the most influential supercapacitor papers, about three times the share of India, which is second. Since 2021–2023, China's share fell by about a fifth and the US share fell by about a quarter.

2021–2025: China 46.3% (1st, about 1,370 of the 2,949 top papers), India 13.9% (2nd), South Korea 7.3% (3rd), Saudi Arabia 3.6% (4th), Pakistan 3.4% (5th), the United States 2.3% (6th, about 67). 2021–2023 to 2024–2025: China 51.0% to 40.5%, the United States 2.6% to 1.8%. All 86 countries and institutions

Top 1%
China leads, 44.4%
Leading Chinese institution
Nanjing Forestry University, 2nd in the world
China's most cited study
Untangling the respective effects of heteroatom-doped carbon materials in batteries, supercapacitors and the ORR to design high performance materials 759 citations

Hydrogen by electrolysis: China leads by a wide margin, South Korea and the United States level for second

Making hydrogen fuel by splitting water with electricity.

China writes about half of the most influential electrolysis papers, about twelve times the United States' share, with South Korea and the United States level behind it. Since 2021–2023, China's share grew by about a third and the US share held steady.

2021–2025: China 53.0% (1st, about 830 of the 1,571 top papers), South Korea 4.6% (2nd), the United States 4.4% (3rd, about 69), Australia 3.9% (4th), Germany 3.7% (5th). 2021–2023 to 2024–2025: China 46.1% to 57.8%, the United States 4.4% to 4.4%. All 83 countries and institutions

Top 1%
China leads, 47.5%
Leading Chinese institution
Chinese Academy of Sciences, 1st in the world
China's most cited study
Clean and Affordable Hydrogen Fuel from Alkaline Water Splitting: Past, Recent Progress, and Future Prospects 1,946 citations

Perovskite solar cells: China leads by a wide margin

A newer class of solar cell that is cheap to make and has caught up with silicon on efficiency.

China writes about half of the most influential perovskite solar-cell papers, about eight times the United States' share. Since 2021–2023, China's share edged up and the US share fell by more than a third.

2021–2025: China 53.9% (1st, about 980 of the 1,818 top papers), the United States 6.5% (2nd, about 120), South Korea 4.6% (3rd), Hong Kong 4.0% (4th), Germany 3.9% (joint 5th). 2021–2023 to 2024–2025: China 49.7% to 58.8%, the United States 8.0% to 4.9%. All 76 countries and institutions

Top 1%
China leads, 44.8%
Leading Chinese institution
Shaanxi Normal University, 1st in the world
China's most cited study
Inactive (PbI 2 ) 2 RbCl stabilizes perovskite films for efficient solar cells 1,444 citations

Beyond China and the United States

South Korea and Germany are next in line in two or more areas each. The highest placing for any other country: India, 2nd in supercapacitors.

CountryElectric batteriesBatteriesSupercapacitorsSupercapacitorsHydrogen by electrolysisHydrogen by electrolysisPerovskite solar cellsPerovskite solar cellsStrongest area
9th1.3%2nd13.9%6th2.5%=5th3.9%Supercapacitors
3rd3.4%3rd7.3%2nd4.6%3rd4.6%Hydrogen by electrolysis
=4th2.2%=17th0.6%5th3.7%=5th3.9%Electric batteries
6th1.9%=9th1.3%4th3.9%12th1.5%Hydrogen by electrolysis
=4th2.2%=9th1.3%7th2.3%7th2.3%Electric batteries
=11th0.5%4th3.6%8th1.7%=8th2.1%Supercapacitors
8th1.5%16th0.7%12th1.1%4th4.0%Perovskite solar cells
=22nd0.2%5th3.4%=26th0.4%13th1.0%Supercapacitors
7th1.7%=17th0.6%9th1.5%=15th0.8%Electric batteries
=11th0.5%=14th0.8%=13th0.9%=10th1.6%Perovskite solar cells
10th0.8%=19th0.5%10th1.4%=15th0.8%Electric batteries
=22nd0.2%7th1.9%=17th0.7%=21st0.4%Supercapacitors

Rank, then share of the most cited papers, 2021–2025. "=" marks a tie. Hover or tap a cell for more; tap a country to follow it through the page.

Does China's lead hold up?

Yes. Counting only the 1% most cited papers, China still leads all four areas it leads overall. Discounting citations that come from China itself beyond what its size predicts, China's supercapacitor share falls from 46.3% to 43.6%, and it still ranks 1st.

Check 1: only the most cited 1% of papers

Each technology's top 1% is a tenth as many papers as its top 10%, so a few papers move it. Hollow: the top 10%. Filled: the top 1%.

Top 10%Top 1%Share of each tier's papers

Electric batteries748 papers in the top 1%
China
Supercapacitors296 papers in the top 1%
China
Hydrogen by electrolysis159 papers in the top 1%
China
Perovskite solar cells184 papers in the top 1%
China
The numbers behind the chart
TechnologyChina, top 10%China, top 1%United States, top 10%United States, top 1%
Electric batteries68.0%57.7%7.6%14.7%
Supercapacitors46.3%44.4%2.3%4.8%
Hydrogen by electrolysis53.0%47.5%4.4%5.8%
Perovskite solar cells53.9%44.8%6.5%12.4%

Check 2: discounting home-country citations

In every area, China's top papers are cited from within China more than its size would predict, 1.2 to 1.6 times as often. Remove that excess and China's supercapacitor share goes from 46.3% to 43.6%; it still leads (the one area recomputed this way so far).

The numbers behind this check

Researchers cite work from their own country more often. This compares how often China's top papers are cited from China with what China's size in the field predicts; the re-ranking removes only the excess.

TechnologyCitations from ChinaExpected from its sizeExcess
Electric batteriesUp to 100 single-country papers77.4%65.7%+11.7 pts
SupercapacitorsEvery top-10% paper66.8%48.0%+18.8 pts
Hydrogen by electrolysisEvery top-10% paper80.6%50.2%+30.4 pts
Perovskite solar cellsEvery top-10% paper76.6%56.0%+20.6 pts

Home citers include authors citing their own earlier work. Re-ranking with the excess removed is computed so far for supercapacitors (China 46.3% → 43.6%), hydrogen by electrolysis (China 53.0% → 45.8%) and perovskite solar cells (China 53.9% → 52.0%).

China's most influential clean energy papers

The most cited papers led from China, 2021–2025. Tap a technology.

  1. High‐Energy Lithium‐Ion Batteries: Recent Progress and a Promising Future in Applications
    2022CN
    Chinese Academy of Sciences, Chongqing Institute of Green and Intelligent Technology and University of Chinese Academy of Sciences
    1,201citations, #3 of 7,469 worldwide
  2. Surface‐Preferred Crystal Plane for a Stable and Reversible Zinc Anode
    2021CN
    Central South University and Hunan University
    1,043citations, #9 of 7,469 worldwide
  3. A Growing Appreciation for the Role of LiF in the Solid Electrolyte Interphase
    2021CNUS
    Fudan University
    1,018citations, #11 of 7,469 worldwide
  4. Self-assembled monolayers direct a LiF-rich interphase toward long-life lithium metal batteries
    2022CNSG
    Zhejiang University of Technology
    958citations, #17 of 7,469 worldwide
  5. Physics-informed neural network for lithium-ion battery degradation stable modeling and prognosis
    2024CN
    Xi'an Jiaotong University
    855citations, #20 of 7,469 worldwide

"Led from China": at least half the author credit is Chinese.

Where China leads within clean energy, and where it does not

China leads 37 of 38 specialist areas; Germany leads techno-economics, hydrogen economy and policy reviews.

Share of the sub-area's papers in the top 10%: China against the strongest other country

Sodium-ion and potassium-ion batteriesElectric batteries, 941 papers
+75.8 pts
Zinc, magnesium and other aqueous or multivalent batteriesElectric batteries, 1,230 papers
+74.9 pts
Lithium-sulfur batteriesElectric batteries, 538 papers
+72.4 pts
Lithium-ion anodes (graphite, silicon)Electric batteries, 567 papers
+71.6 pts
Hybrid electrolysis (hydrazine or organic oxidation)Hydrogen by electrolysis, 127 papers
+70.3 pts
Acidic oxygen-evolution catalysts for PEM electrolysis (Ir, Ru)Hydrogen by electrolysis, 236 papers
+63.8 pts
Hydrogen-evolution catalystsHydrogen by electrolysis, 180 papers
+62.9 pts
Seawater electrolysisHydrogen by electrolysis, 112 papers
+62.8 pts
Defect and surface passivation (incl. 2D/3D heterojunctions)Perovskite solar cells, 306 papers
+62.2 pts
Bifunctional catalysts for overall water splittingHydrogen by electrolysis, 187 papers
+60.6 pts
Electron-transport layers and buried interfacesPerovskite solar cells, 168 papers
+58.1 pts
Alkaline oxygen-evolution catalysts (Ni, Co, Fe)Hydrogen by electrolysis, 180 papers
+57.4 pts
Perovskite composition, film growth and crystallisationPerovskite solar cells, 246 papers
+56.8 pts
Hole-transport layers and self-assembled monolayersPerovskite solar cells, 278 papers
+54.9 pts
Flexible, wearable, micro and structural supercapacitorsSupercapacitors, 313 papers
+54.7 pts
Liquid electrolytes and interphasesElectric batteries, 533 papers
+54.4 pts
Battery management, modelling, thermal and safetyElectric batteries, 1,288 papers
+53.7 pts
Porous and biomass-derived carbon electrodesSupercapacitors, 481 papers
+53.2 pts
Lithium metal anodesElectric batteries, 340 papers
+53.0 pts
Lithium-ion cathode materialsElectric batteries, 418 papers
+51.2 pts
Large-area modules, flexible and indoor cellsPerovskite solar cells, 163 papers
+50.5 pts
Tandem solar cells (perovskite-silicon, all-perovskite)Perovskite solar cells, 119 papers
+50.3 pts
Hybrid and metal-ion capacitors (incl. zinc-ion)Supercapacitors, 208 papers
+48.3 pts
Solid-state batteries and solid electrolytesElectric batteries, 940 papers
+46.5 pts
Battery recycling and materials recoveryElectric batteries, 391 papers
+44.5 pts
Redox flow batteriesElectric batteries, 92 papers
+40.9 pts
MXene-based electrodesSupercapacitors, 326 papers
+31.2 pts
Metal-organic and covalent-organic framework materialsSupercapacitors, 207 papers
+28.2 pts
Metal sulfide, phosphide, nitride and other compound electrodesSupercapacitors, 286 papers
+26.6 pts
Stability, degradation and encapsulationPerovskite solar cells, 161 papers
+21.7 pts
Metal oxide and hydroxide electrodesSupercapacitors, 500 papers
+17.3 pts
Renewable-powered hydrogen systems and energy-system optimisationHydrogen by electrolysis, 136 papers
+13.4 pts
Electrolyser technologies and stacks (PEM, alkaline, solid oxide)Hydrogen by electrolysis, 75 papers
+12.8 pts
Graphene and carbon-nanotube electrodesSupercapacitors, 141 papers
+12.6 pts
Conducting-polymer electrodesSupercapacitors, 139 papers
+9.2 pts
Mechanisms, electrolytes, modelling and general reviewsSupercapacitors, 232 papers
+9.0 pts
Lead-free and inorganic perovskites (incl. device simulation)Perovskite solar cells, 240 papers
+8.9 pts
Techno-economics, hydrogen economy and policy reviewsHydrogen by electrolysis, 213 papers
GermanyDE
The numbers behind the chart
Sub-areaTechnologyPapersChinaStrongest other country
Sodium-ion and potassium-ion batteriesElectric batteries94179.8% (1st)United States 4.0%
Zinc, magnesium and other aqueous or multivalent batteriesElectric batteries1,23078.0% (1st)United States 3.1%
Lithium-sulfur batteriesElectric batteries53877.5% (1st)United States 5.1%
Lithium-ion anodes (graphite, silicon)Electric batteries56776.9% (1st)United States 5.3%
Hybrid electrolysis (hydrazine or organic oxidation)Hydrogen by electrolysis12775.9% (1st)South Korea 5.6%
Acidic oxygen-evolution catalysts for PEM electrolysis (Ir, Ru)Hydrogen by electrolysis23668.2% (1st)United States 4.4%
Hydrogen-evolution catalystsHydrogen by electrolysis18067.1% (1st)United States 4.2%
Seawater electrolysisHydrogen by electrolysis11270.1% (1st)Australia 7.3%
Defect and surface passivation (incl. 2D/3D heterojunctions)Perovskite solar cells30667.9% (1st)United States 5.7%
Bifunctional catalysts for overall water splittingHydrogen by electrolysis18771.6% (1st)South Korea 11.0%
Electron-transport layers and buried interfacesPerovskite solar cells16865.1% (1st)South Korea 7.0%
Alkaline oxygen-evolution catalysts (Ni, Co, Fe)Hydrogen by electrolysis18062.2% (1st)South Korea 4.8%
Perovskite composition, film growth and crystallisationPerovskite solar cells24664.3% (1st)South Korea 7.5%
Hole-transport layers and self-assembled monolayersPerovskite solar cells27861.8% (1st)Hong Kong 6.9%
Flexible, wearable, micro and structural supercapacitorsSupercapacitors31362.0% (1st)South Korea 7.3%
Liquid electrolytes and interphasesElectric batteries53367.0% (1st)United States 12.6%
Battery management, modelling, thermal and safetyElectric batteries1,28859.5% (1st)United States 5.8%
Porous and biomass-derived carbon electrodesSupercapacitors48161.1% (1st)India 7.9%
Lithium metal anodesElectric batteries34067.3% (1st)United States 14.3%
Lithium-ion cathode materialsElectric batteries41863.0% (1st)United States 11.8%
Large-area modules, flexible and indoor cellsPerovskite solar cells16356.4% (1st)United States 5.9%
Tandem solar cells (perovskite-silicon, all-perovskite)Perovskite solar cells11958.3% (1st)United States 8.0%
Hybrid and metal-ion capacitors (incl. zinc-ion)Supercapacitors20860.2% (1st)South Korea 11.9%
Solid-state batteries and solid electrolytesElectric batteries94059.7% (1st)United States 13.2%
Battery recycling and materials recoveryElectric batteries39154.2% (1st)United States 9.7%
Redox flow batteriesElectric batteries9252.9% (1st)United States 12.0%
MXene-based electrodesSupercapacitors32644.3% (1st)India 13.1%
Metal-organic and covalent-organic framework materialsSupercapacitors20743.4% (1st)India 15.2%
Metal sulfide, phosphide, nitride and other compound electrodesSupercapacitors28640.6% (1st)India 14.0%
Stability, degradation and encapsulationPerovskite solar cells16142.2% (1st)United States 20.5%
Metal oxide and hydroxide electrodesSupercapacitors50038.3% (1st)India 21.0%
Renewable-powered hydrogen systems and energy-system optimisationHydrogen by electrolysis13619.7% (1st)United Kingdom 6.3%
Electrolyser technologies and stacks (PEM, alkaline, solid oxide)Hydrogen by electrolysis7520.6% (1st)Germany 7.8%
Graphene and carbon-nanotube electrodesSupercapacitors14132.2% (1st)India 19.6%
Conducting-polymer electrodesSupercapacitors13931.3% (1st)India 22.1%
Mechanisms, electrolytes, modelling and general reviewsSupercapacitors23230.7% (1st)India 21.7%
Lead-free and inorganic perovskites (incl. device simulation)Perovskite solar cells24026.2% (1st)India 17.3%
Techno-economics, hydrogen economy and policy reviewsHydrogen by electrolysis2138.0% (2nd)Germany 8.2%

Specialist areas sorted by an AI model reading each paper (92% agreement with hand labels).

The universities behind China's lead

Chinese Academy of Sciences is in the world's top ten in all four areas, more than any other Chinese institution.

  1. Chinese Academy of Sciences4th in electric batteries, 10th in supercapacitors, 1st in hydrogen by electrolysis, 2nd in perovskite solar cells
  2. Nankai University7th in electric batteries, 5th in hydrogen by electrolysis, 8th in perovskite solar cells
  3. Tsinghua University2nd in electric batteries, 8th in hydrogen by electrolysis
  4. University of Science and Technology of China5th in electric batteries, 3rd in hydrogen by electrolysis
  5. Harbin Institute of Technology6th in electric batteries, 4th in hydrogen by electrolysis
  6. Zhejiang University10th in electric batteries, 6th in hydrogen by electrolysis
  7. Central South University1st in electric batteries
  8. Shaanxi Normal University1st in perovskite solar cells

Who China writes its top papers with

  1. USUnited States680
  2. HKHong Kong475
  3. AUAustralia433
  4. GBUnited Kingdom267
  5. DEGermany236

Questions

Which country leads clean energy research, China or the United States?

As of October 2026, China leads all four clean energy areas tracked here, by share of the most cited research papers from 2021–2025: electric batteries (68.0%), supercapacitors (46.3%), hydrogen by electrolysis (53.0%) and perovskite solar cells (53.9%).

How do Canada, India, the UK and other countries rank in clean energy research?

Their best placings: Canada 7th in electric batteries, India 2nd in supercapacitors, United Kingdom joint 4th in electric batteries, South Korea 2nd in hydrogen by electrolysis, Germany joint 4th in electric batteries and Japan joint 10th in perovskite solar cells. Pick any country at the top of the page to see its rank in each area.

Is China's share of top clean energy research growing?

In three of four areas, comparing 2021–2023 with 2024–2025: electric batteries from 64.0% to 72.0%, hydrogen by electrolysis from 46.1% to 57.8% and perovskite solar cells from 49.7% to 58.8%.

Which Chinese universities lead clean energy research?

Chinese Academy of Sciences is in the world's top ten in all four areas, more than any other Chinese institution. Also in a world top ten: Nankai University, Tsinghua University and University of Science and Technology of China.

What is China's most cited clean energy paper?

"Clean and Affordable Hydrogen Fuel from Alkaline Water Splitting: Past, Recent Progress, and Future Prospects" (2021) with 1,946 citations, the most of any clean energy paper led from China in 2021–2025 across these four areas.

What does this measure, and what does it not?

Each country's share of the 10% most cited research papers published 2021–2025, with each paper's credit split between its authors' countries. Four technologies stand for clean energy here: electric batteries, supercapacitors, hydrogen made by electrolysis, and perovskite solar cells. It does not measure factory capacity, battery or solar panel production, installed power, prices, companies or exports. How it's measured.

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Hamadeh, K. (2026). China in clean energy research. World Tech Rankings. Data: OpenAlex, pulled 24 October 2026. https://worldtechrankings.com/china/energy/

How this is measured

Most cited papers
For each technology and year, the 10% of papers that other researchers cite most, from OpenAlex, an open catalogue of research. Ranking within each year stops older papers crowding out newer ones.
A country's share
Each paper's credit is split between its authors' countries: a paper with two Chinese and two American authors counts half to each. A country's share is its credit divided by all credit.
The top 1%
The same, for the 1% most cited papers: a tenth as many papers, so it moves more with a few of them.
Home-country citations
Citations from a paper's own country beyond what the country's size in the field predicts. Removing them is a test of whether a lead rests on self-citation.
Sub-areas
Each top paper is sorted into one sub-area by an AI model reading its title and abstract, checked against 200 hand-labelled papers (92% agreement).
What it is not
Four technologies stand for clean energy here: electric batteries, supercapacitors, hydrogen made by electrolysis, and perovskite solar cells. It does not measure factory capacity, battery or solar panel production, installed power, prices, companies or exports. Research leadership and industrial leadership can differ.

Data: OpenAlex, pulled 24 October 2026; definition version 0.5. Every number on this page is recomputed from the data on each update. Full method.

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