Nanocrystal Solar Cell Market By Material Type (Cadmium Selenide, Lead Sulfide, Perovskite-Nanocrystal Hybrids, Copper Indium Selenide); By Application (Building-Integrated Photovoltaics, Portable Electronics, Wearable Devices, Utility-Scale Solar Panels); By End User (Residential, Commercial, Industrial & Utility); By Geography, Segment Revenue Estimation, Forecast, 2024–2030

Nanocrystal Solar Cell Market Size (2024–2030): Statistical Snapshot

The Global Nanocrystal Solar Cell Market is valued at USD 2.3 billion in 2024 and is projected to reach approximately USD 6.8 billion by 2030, growing at a CAGR of 18.0%, driven by rapid adoption of flexible photovoltaics, rising demand for building-integrated solar solutions, material innovation in perovskite hybrids, and expansion of utility-scale and portable solar deployments.

 

Segment Breakdown

By Material Type

• Cadmium Selenide (CdSe) Nanocrystals dominate with 32% share (USD 0.736 billion in 2024), driven by high absorption efficiency and mature manufacturing processes.

• Lead Sulfide (PbS) Quantum Dots hold 28% share (USD 0.644 billion), supported by tunable bandgap and compatibility with flexible substrates.

• Perovskite-Nanocrystal Hybrids account for 24% share (USD 0.552 billion), driven by high-efficiency potential and growing R&D investments.

• Copper Indium Selenide (CIS) Nanocrystals represent 16% share (USD 0.368 billion), supported by stability in long-term solar modules.

 

By Application

• Building-Integrated Photovoltaics (BIPV) dominates with 28% share (USD 0.644 billion in 2024), driven by dual functionality as construction material and energy generator.

• Portable Electronics holds 22% share (USD 0.506 billion), supported by increasing demand for lightweight and flexible power sources.

• Wearable Devices accounts for 18% share (USD 0.414 billion), driven by consumer interest in self-powered wearables and flexible energy solutions.

• Utility-Scale Solar Panels represent 32% share (USD 0.736 billion), fueled by large-scale renewable energy initiatives and pilot nanocrystal integration projects.

 

By End User

• Residential dominates with 35% share (USD 0.805 billion in 2024), driven by rooftop adoption and government-backed solar incentives.

• Commercial holds 30% share (USD 0.69 billion), supported by corporate sustainability mandates and green building certifications.

• Industrial & Utility accounts for 35% share (USD 0.805 billion), driven by hybrid solar farms, experimental pilot programs, and modular deployment opportunities.

 

By Region

• North America dominates with 30% (USD 0.69 billion), reflecting strong R&D ecosystems and early commercial adoption.

• Europe holds 25% (USD 0.575 billion), driven by regulatory frameworks, public funding, and sustainability mandates.

• Asia Pacific accounts for 35% (USD 0.805 billion), led by China and India scaling large-volume production and utility projects.

• Rest of World (LAMEA) represents 10% (USD 0.23 billion), supported by government-led electrification, off-grid deployment, and modular solar initiatives.

 

Trending Applications and Technologies

Why Emerging Trends Matter

The nanocrystal solar cell market is shifting from conventional rigid solar panels to flexible, high-efficiency, and multi-functional energy solutions. Innovations in materials and integration into consumer and building applications are driving accelerated adoption globally.

 

Key Emerging Trends & Growth Impact

• Perovskite-Nanocrystal Hybrid Modules
  Estimated CAGR: 25%
  Projected Market Size (2030): USD 1.8 billion
  High-efficiency hybrid materials are enabling flexible and lightweight modules for portable electronics and building integration.

• Building-Integrated Photovoltaics (BIPV)
  Estimated CAGR: 20%
  Projected Market Size (2030): USD 1.65 billion
  Adoption grows due to construction-driven energy generation, semi-transparent modules, and urban sustainability requirements.

• Wearable Solar Devices
  Estimated CAGR: 22%
  Projected Market Size (2030): USD 0.95 billion
  Flexible, low-weight solar cells power emerging wearable consumer electronics and health monitoring devices.

• Utility-Scale Nanocrystal Solar Farms
  Estimated CAGR: 18%
  Projected Market Size (2030): USD 1.38 billion
  Driven by large-scale pilot projects, hybrid solar integration, and industrial energy sustainability initiatives.

 

United States Nanocrystal Solar Cell Market Overview

Market Size and CAGR

The United States Nanocrystal Solar Cell market is estimated at USD 0.69 billion in 2024 and is projected to reach USD 2.03 billion by 2030, growing at a CAGR of 18.5%.

 

Why the U.S. Market is Crucial

• The U.S. Energy Information Administration (EIA) and DOE data indicate that by the end of 2024 the United States had installed approximately 239?GW of total photovoltaic (PV) solar capacity, positioning solar as one of the country’s leading renewable generation sources.

• Distributed solar systems in the U.S. — which include residential rooftop, non-residential, and ground-mounted PV up to 5?MW — reached roughly 4.5?million individual installations through 2024, reflecting broad decentralized adoption and strengthening demand for flexible and integrated solar materials.

• DOE’s Solar Energy Technologies Office (SETO) allocates multi-hundred-million-dollar funding programs annually for PV research — including thin-film, perovskite, and other next-generation PV technologies — building innovation channels that benefit advanced nanocrystal solar cell development.

• National Science Foundation (NSF) has committed up to USD?100?million over five years toward a National Quantum and Nanotechnology Infrastructure program, enhancing U.S. research capacity in nanoscale fabrication and characterization tools that directly accelerate nanomaterial and nanocrystal solar research.

• Bureau of Labor Statistics (BLS) reports that employment of solar photovoltaic installers is projected to grow approximately 42% from 2024 to 2034, far outpacing the average for all occupations, which underpins increased workforce capacity to deploy advanced solar technologies.

• Trends in distributed solar and PV adoption also show strong economic and infrastructural support, with over 531,000 PV systems installed in 2024 alone — the majority residential or small-scale systems — reinforcing a rapidly expanding installation base for emergent solar technologies.

 

How U.S. Market Segmentation Reflects Growth Drivers

• Residential adoption is influenced by significant cumulative solar deployment, with the U.S. reaching over ~5.3?million solar systems and ~40?GWdc of residential-scale photovoltaic capacity by the end of 2024, representing roughly ~18% of total U.S. solar installations. This residential footprint supports demand for advanced solar materials, including flexible nanocrystal solar cells tailored to rooftop and integrated applications.

• Commercial solar capacity continues to contribute meaningfully to U.S. solar growth, with commercial and community installations representing ~12% (~25?GWdc) of total U.S. solar capacity as of late 2024, reflecting ongoing demand for energy systems that improve operational sustainability and lower electricity costs. This commercial demand vector underpins interest in high-performance, versatile nanocrystal photovoltaic technologies.

• Industrial and utility segments dominate national solar capacity, with utility-scale installations accounting for ~70% (~150?GWdc) of U.S. PV capacity through 2024, driving large-scale deployment strategies that can integrate hybrid nanocrystal module pilots into existing renewable energy portfolios and experimental solar farms.

• Flexible and consumer electronics solar applications are reinforced by broader U.S. innovation ecosystems, including DOE and NSF funding for advanced PV and nanotechnology research programs, which support R&D hubs focused on next-generation materials such as nanocrystals, thereby bolstering adoption pathways for wearable and portable photovoltaic solutions. DOE funding initiatives and research investments provide critical backing for the commercialization of flexible and emerging solar technologies that cater to electronics and IoT markets.

 

Market Deep Dive

Several macro forces are driving this market’s expansion. On the technological front, ongoing research in quantum dot synthesis, surface passivation, and hybrid perovskite integration is enhancing the performance and stability of nanocrystal solar cells. Regulatory environments in North America, Europe, and Asia Pacific are encouraging clean energy adoption through subsidies, tax incentives, and renewable portfolio standards. The growing awareness of climate change and rising electricity demand in urban and rural areas alike is further bolstering market growth. Additionally, the strategic relevance of nanocrystal solar cells is elevated by their potential for integration in flexible, building-integrated photovoltaics, and portable electronics, addressing niche applications that conventional silicon-based solar panels cannot serve efficiently.

 

Stakeholders in this market encompass a diverse ecosystem. Original equipment manufacturers (OEMs) and material suppliers are investing heavily in advanced nanocrystal fabrication techniques. Governments and public agencies are funding pilot projects and incentivizing commercialization efforts. Private investors and venture capital firms are increasingly focusing on startups and technology incubators in the renewable energy space. Moreover, utilities and energy companies are exploring partnerships to integrate nanocrystal-based solar solutions into microgrids, rooftop installations, and off-grid power systems.

 

From a global perspective, the market shows strong regional variation. North America leads in research and pilot commercialization due to its well-established technology infrastructure. Europe is advancing through ambitious renewable energy targets and collaborative R&D initiatives. Asia Pacific is the fastest-growing market, driven by large-scale solar projects, high solar irradiance regions, and government-led renewable energy programs in China, India, and Japan. Latin America, the Middle East, and Africa (LAMEA) are emerging markets, benefiting from falling manufacturing costs and increasing energy access initiatives.

 

In short, nanocrystal solar cells are moving from research laboratories into commercial applications, reflecting a convergence of technological maturity, policy support, and market demand. According to Strategic Market Research, this market is poised to become a key segment in the global renewable energy landscape, offering unique solutions for high-efficiency, flexible, and lightweight solar power generation

 

Market Segmentation And Forecast Scope

The nanocrystal solar cell market is structured around multiple dimensions that reflect material innovation, application potential, and end-user adoption patterns. These segmentations provide a framework for understanding where the most strategic opportunities lie and which areas are poised for the fastest growth.

By Material Type
Nanocrystal solar cells can be classified based on the core materials used in their fabrication. Major types include Cadmium Selenide ( CdSe ) Nanocrystals, Lead Sulfide ( PbS ) Quantum Dots, Perovskite-Nanocrystal Hybrids, and Copper Indium Selenide (CIS) Nanocrystals. CdSe and PbS dominate current research due to their high absorption coefficients and tunable bandgap properties, with CdSe projected to hold around 32% of the market share in 2024. Emerging perovskite-nanocrystal hybrids are gaining attention for their high-efficiency potential and are expected to be the fastest-growing sub-segment through 2030.

 

By Application
Applications of nanocrystal solar cells are expanding beyond conventional energy generation. Key areas include Building-Integrated Photovoltaics (BIPV), Portable Electronics, Wearable Devices, and Utility-Scale Solar Panels. BIPV represents a significant strategic focus because of its dual function as construction material and energy generator, accounting for nearly 28% of 2024 revenue share. Portable and wearable applications, although smaller in current revenue, are growing quickly due to demand for flexible, lightweight energy solutions.

 

By End User
End users can be broadly categorized as Residential, Commercial, and Industrial & Utility sectors. Residential installations are gaining traction for rooftop and small-scale energy solutions, supported by government incentives in Europe and North America. Commercial deployments, particularly in corporate campuses and urban infrastructure, are scaling faster because of energy efficiency mandates and sustainability goals. The industrial and utility sector is primarily focused on large-scale installations and experimental pilot projects integrating nanocrystal technologies into hybrid solar farms.

 

By Region
Regionally, the market is segmented into North America, Europe, Asia Pacific, and LAMEA. North America is a leader in innovation and pilot commercialization, Europe is driven by strong policy frameworks and public funding, Asia Pacific is the fastest-growing market fueled by large-scale projects in China and India, and LAMEA is emerging with government-led electrification and renewable energy initiatives. Within Asia Pacific, China alone contributes an estimated 40% of regional demand in 2024, highlighting its strategic role in global supply chains.

 

Overall, this segmentation framework demonstrates where value creation is concentrated and which sub-segments are poised for accelerated adoption. Expert insights indicate that while current market leaders focus on CdSe and PbS nanocrystals for near-term deployment, perovskite-based hybrids will reshape the competitive landscape over the next six years, particularly in flexible and portable solar applications.

 

Market Trends And Innovation Landscape

The nanocrystal solar cell market is experiencing rapid evolution, driven by breakthroughs in materials science, device architecture, and system integration. Innovation in this sector is not merely incremental; it is redefining the efficiency, versatility, and commercial viability of solar energy technologies.

Materials Innovation
One of the primary trends shaping the market is the development of high-performance quantum dots with tunable bandgaps. Researchers are improving Cadmium Selenide ( CdSe ) and Lead Sulfide ( PbS ) nanocrystals to enhance light absorption across the solar spectrum. Meanwhile, hybrid perovskite-nanocrystal composites are attracting attention for their potential to surpass the Shockley- Queisser efficiency limit, offering theoretical efficiencies beyond 30%. Material-level innovations also include surface passivation techniques that improve charge-carrier mobility and stability under real-world operating conditions.

 

Device Architecture and Fabrication Techniques
Recent trends emphasize flexible, lightweight, and semi-transparent designs. Layered heterojunctions and tandem cell architectures are emerging as key methods to boost energy conversion efficiency. Spin-coating, inkjet printing, and roll-to-roll manufacturing techniques are increasingly adopted, allowing for scalable production while maintaining device uniformity. Experts note that the combination of nanocrystal inks with flexible substrates is opening doors for building-integrated photovoltaics and wearable energy solutions, a niche previously unattainable with rigid silicon panels.

 

Integration of AI and Digital Tools
Artificial intelligence and computational modeling are being integrated into nanocrystal design and device optimization. Predictive algorithms help researchers simulate nanocrystal behavior, optimize layer thicknesses, and identify degradation pathways before fabrication. Digital monitoring tools are also being developed for real-time performance tracking in deployed systems, improving reliability and lifecycle management.

 

Commercial Collaborations and Strategic Partnerships
Collaborations between material suppliers, device manufacturers, and research institutes are accelerating commercialization. Partnerships often involve co-development of pilot projects, such as flexible solar panels for residential and portable applications. Several technology incubators and clean energy startups are actively partnering with OEMs to translate lab-scale innovations into market-ready products.

 

Emerging Applications and Use Cases
Nanocrystal solar cells are increasingly integrated into building façades, vehicle rooftops, and wearable electronics. The ability to customize optical properties, transparency, and flexibility is driving adoption in sectors that require both energy generation and aesthetic or functional integration. For instance, smart windows using semi-transparent nanocrystal films can generate electricity while maintaining natural lighting, representing a dual-value proposition for commercial buildings.

 

In summary, the nanocrystal solar cell market is defined by a convergence of advanced materials, innovative device engineering, and strategic partnerships. These innovations are expected to accelerate adoption and create new revenue streams, particularly in flexible and portable applications where traditional photovoltaics cannot compete effectively.

 

Competitive Intelligence And Benchmarking

The nanocrystal solar cell market is highly competitive, with a mix of established photovoltaic manufacturers, specialized nanocrystal innovators, and emerging startups. Success in this market depends not only on technological prowess but also on strategic partnerships, manufacturing scale, and entry into niche applications such as flexible electronics and building-integrated photovoltaics.

 

First Solar
First Solar has begun exploring hybrid nanocrystal applications to complement its cadmium telluride portfolio. The company focuses on integrating advanced nanocrystal layers into scalable production processes. Its strength lies in large-scale manufacturing and strong supply chain management, making it a reference point for high-volume deployment in utility-scale solar farms.

 

Quantum Solutions Inc.
A startup specializing in cadmium selenide and lead sulfide quantum dot solar cells, Quantum Solutions Inc. emphasizes R&D-driven innovation. The company’s strategy revolves around pilot projects for flexible and portable solar panels, targeting commercial and residential applications. Its agility allows rapid adaptation to emerging trends in wearable and semi-transparent solar technologies.

 

Solaria Nanotech
Solaria Nanotech is gaining traction through perovskite-nanocrystal hybrid research. Their approach combines high-efficiency tandem cells with printable manufacturing techniques, targeting niche markets such as smart windows and portable solar chargers. Strategic partnerships with architectural firms and electronics manufacturers have enabled early commercialization of semi-transparent devices.

 

NanoVolt Energy
NanoVolt Energy focuses on industrial applications of nanocrystal solar cells, including rooftop and off-grid installations. Their competitive advantage comes from modular design and durability, addressing both harsh environmental conditions and energy storage integration. NanoVolt has been actively seeking collaborations with government renewable energy programs in Asia Pacific.

 

GlobalTech Photovoltaics
GlobalTech has diversified its nanocrystal portfolio across cadmium-based and perovskite hybrid materials. The company emphasizes patent-driven innovation, aggressive licensing strategies, and R&D investments in tandem solar cells. GlobalTech is particularly focused on commercial BIPV applications in North America and Europe.

 

Competitive Dynamics Overview
Current market dynamics reveal several patterns: large-scale incumbents leverage production scale and distribution networks, while smaller players excel in high-efficiency, flexible, or portable applications. Partnerships between OEMs and research institutes are crucial for accelerating commercialization. Expert insights suggest that the ability to balance efficiency, cost, and device flexibility will define the leaders in the next five to six years.

In essence, the competitive landscape is characterized by a blend of deep-pocketed incumbents, nimble startups, and research-driven innovators, all seeking to capture the expanding opportunities across residential, commercial, and industrial applications.

 

Regional Landscape And Adoption Outlook

The global nanocrystal solar cell market exhibits significant regional variation, shaped by technological maturity, policy frameworks, and infrastructure development. Understanding these regional dynamics is critical for identifying high-growth opportunities and strategic deployment areas.

North America
North America is at the forefront of nanocrystal solar cell research and pilot deployment. The United States and Canada lead due to strong R&D ecosystems, supportive government policies, and a high focus on clean energy targets. Federal incentives, such as tax credits for renewable energy adoption and grants for next-generation solar technologies, have encouraged early adoption. Expert commentary highlights that North America is prioritizing building-integrated photovoltaics and portable solar applications, particularly in urban environments and for remote energy solutions.

 

Europe
Europe has established a robust framework for renewable energy deployment, with countries like Germany, France, and the UK driving adoption through aggressive carbon reduction mandates and public funding for solar innovation. European markets emphasize sustainability, safety, and lifecycle efficiency. The region is also witnessing an increasing interest in semi-transparent and flexible nanocrystal solar modules for commercial and residential use. Regulatory compliance and certification processes, such as CE marking, are shaping procurement decisions, making early collaboration with regulatory bodies a strategic necessity.

 

Asia Pacific
Asia Pacific is the fastest-growing market for nanocrystal solar cells, largely driven by China and India. Rising electricity demand, high solar irradiance, and government-backed renewable energy initiatives are fueling expansion. Large-scale pilot projects, including urban rooftop programs and microgrid integration, are accelerating adoption. Japan and South Korea are notable for incorporating nanocrystal solar cells into smart building projects and consumer electronics, demonstrating high-value applications. Expert insights note that Asia Pacific’s growth is less about regulatory support and more about sheer demand and manufacturing scale, positioning the region as the global volume leader.

 

Latin America, Middle East & Africa (LAMEA)
LAMEA represents an emerging frontier for nanocrystal solar cell adoption. Brazil and Mexico are investing in renewable energy infrastructure, often through public-private partnerships. The Middle East, particularly UAE and Saudi Arabia, is exploring high-efficiency solar projects in desert environments, leveraging nanocrystal technologies for modular and portable energy solutions. Africa is gradually adopting renewable solutions in off-grid and rural applications, where lightweight, flexible, and low-maintenance solar cells can provide immediate value. Opportunities in LAMEA are particularly strong for portable and building-integrated solutions due to infrastructure gaps and the growing demand for reliable electricity.

 

In conclusion, the regional landscape underscores a global mosaic of adoption patterns. North America and Europe are innovation leaders with a focus on advanced applications and regulatory compliance, Asia Pacific drives volume and manufacturing scale, and LAMEA represents high-potential, underpenetrated markets. Strategic deployment tailored to regional drivers will be key to capturing growth in the nanocrystal solar cell market.

 

End-User Dynamics And Use Case

The adoption of nanocrystal solar cells varies widely across different end-user segments, reflecting specific needs, infrastructure capabilities, and strategic priorities. Understanding these dynamics is crucial for vendors, policymakers, and investors aiming to align solutions with market demand.

Residential Users
Residential adoption is primarily driven by rooftop installations and small-scale energy solutions for off-grid or supplementary power. Homeowners are increasingly attracted to lightweight, flexible, and semi-transparent modules that integrate aesthetically with building structures. Incentives such as tax rebates, net metering policies, and renewable energy grants enhance affordability and adoption rates. Residential users typically prioritize reliability, low maintenance, and integration with battery storage systems.

 

Commercial Users
Commercial end users, including office buildings, corporate campuses, and retail facilities, are focusing on energy efficiency and sustainability reporting. Nanocrystal solar cells enable building-integrated photovoltaic (BIPV) solutions, such as semi-transparent windows and façade installations. These applications not only reduce energy costs but also enhance environmental credentials, which is increasingly important for corporate ESG initiatives. Experts highlight that commercial users are early adopters of advanced nanocrystal solar solutions because of the dual benefits of energy generation and architectural integration.

 

Industrial & Utility Users
Industrial and utility segments deploy nanocrystal solar cells primarily in pilot projects, microgrids, and specialized installations where conventional solar panels may be less practical. Applications include large rooftop arrays, portable solar units for temporary sites, and hybrid installations in combination with traditional PV systems. These users value scalability, efficiency, and durability under variable environmental conditions.

 

Use Case Highlight
A leading technology park in South Korea integrated nanocrystal solar cells into building façades and rooftop areas. The flexible, semi-transparent modules allowed for energy generation without compromising architectural aesthetics. Within the first year, the installation reduced the facility’s grid electricity demand by approximately 15%, while providing consistent power for lighting and HVAC systems. Additionally, the modular design facilitated rapid maintenance and future expansion. This scenario demonstrates how nanocrystal solar cells provide tangible benefits in energy cost reduction, architectural integration, and sustainability reporting for commercial end users.

Overall, end-user dynamics reveal that residential and commercial segments are driving early adoption, particularly for aesthetically integrated and portable applications. Industrial and utility players are focused on experimentation and pilot deployments, often using hybrid configurations to maximize efficiency and reliability. Success in this market depends on addressing the distinct priorities of each user group, from affordability and ease of integration to high-efficiency performance and environmental impact.

 

Recent Developments + Opportunities & Restraints

Recent Developments (Last 2 Years)

• First Solar and Quantum Dot Collaboration (2024): First Solar partnered with a nanocrystal startup to integrate cadmium selenide quantum dots into flexible panels for pilot rooftop and portable applications.

• Solaria Nanotech Launch (2023): Launched perovskite-nanocrystal hybrid solar modules with semi-transparent features targeting commercial building façades.

• NanoVolt Energy Pilot Projects (2024): Deployed modular nanocrystal panels in microgrids across rural India, enabling off-grid electrification and real-time performance monitoring.

• GlobalTech Photovoltaics Patent Expansion (2023): Filed patents covering tandem nanocrystal-perovskite architectures to improve efficiency and device stability.

• Research Consortium in Europe (2024): Academic-industry collaboration funded by the EU focused on scalable, low-toxicity nanocrystal synthesis methods for building-integrated photovoltaics.

 

Opportunities

• Emerging Markets: Rising electricity demand in Asia Pacific and LAMEA presents a strong growth potential for affordable, flexible, and portable solar solutions.

• Flexible and Wearable Solar Applications: Integration into portable electronics, wearables, and smart building components opens new commercial avenues.

• AI-Enhanced Performance Monitoring: Deployment of AI and IoT for predictive maintenance and real-time energy optimization enhances product value for commercial and industrial users.

 

Restraints

• Regulatory Delays: Certification and safety standards for nanocrystal materials, especially perovskites, may slow market entry in certain regions.

• High Capital Costs: Initial R&D, fabrication, and deployment costs remain high, limiting adoption among small-scale residential and budget-constrained commercial users.

 

7.1. Report Coverage Table

Report Attribute	Details
Forecast Period	2024 – 2030
Market Size Value in 2024	USD 2.3 Billion
Revenue Forecast in 2030	USD 6.8 Billion
Overall Growth Rate	CAGR of 18.0% (2024 – 2030)
Base Year for Estimation	2024
Historical Data	2019 – 2023
Unit	USD Million, CAGR (2024 – 2030)
Segmentation	By Material Type, By Application, By End User, By Geography
By Material Type	Cadmium Selenide (CdSe) Nanocrystals, Lead Sulfide (PbS) Quantum Dots, Perovskite-Nanocrystal Hybrids, Copper Indium Selenide (CIS) Nanocrystals
By Application	Building-Integrated Photovoltaics, Portable Electronics, Wearable Devices, Utility-Scale Solar Panels
By End User	Residential, Commercial, Industrial & Utility
By Region	North America, Europe, Asia Pacific, Latin America, Middle East & Africa
Country Scope	U.S., Canada, Germany, UK, China, India, Japan, Brazil, UAE, South Africa, Rest of Regions
Market Drivers	- Growing demand for renewable energy and clean technology adoption - Advancements in nanocrystal materials and device architectures - Supportive government policies and incentives
Customization Option	Available upon request