Frequently Asked Questions
Corporate
How can indoor solar cells solve future IoT power challenges?
IoT deployment is accelerating, increasing the number of wireless low-power devices across industries. Powering this growing volume with disposable batteries creates significant challenges in cost, maintenance, and sustainability.
Indoor solar cells (indoor photovoltaics) offer a scalable alternative by capturing ambient indoor light and converting it into continuous power.
Why does Epishine focus on indoor solar cells?
Most wireless low-power electronics operate indoors, where light levels are significantly lower than outdoors. Traditional solar cells are designed for direct sunlight and perform poorly in low-light conditions.
Epishine develops indoor solar cells (indoor photovoltaics, IPV) specifically optimized to capture low indoor light efficiently. Our technology delivers reliable performance where most other solar cells generate very little power.
Epishine combines low-light optimized advanced photonic materials with roll-to-roll manufacturing — enabling a new manufacturing paradigm for electronics: scalable, cost-efficient, and sustainable.
Where are Epishine indoor solar cells manufactured?
Epishine’s indoor solar cells are manufactured in our facility in Linköping, Sweden.
What is the difference between indoor and outdoor photovoltaics?
An indoor photovoltaic (IPV) cell works according to the same fundamental physics as an outdoor solar cell. The key difference is the type of light and the intensity of light it is designed to capture.
Indoor lighting contains mainly visible wavelengths, while sunlight also includes large amounts of infrared. Because of this difference in spectrum, indoor PV uses semiconductor materials with slightly higher bandgaps, which are better at converting visible light, whereas outdoor PV uses materials optimized for the full solar spectrum.
The intensity of light is also different. Indoor light is about 1,000 times weaker than sunlight, meaning an indoor cell generates extremely small currents. Outdoors, large currents make resistive losses in the electrodes a major concern. Indoors, resistive losses matter far less; instead, the tiny photocurrents must compete with equally tiny leakage currents caused by microscopic defects in the PV device. Minimizing this leakage current is therefore one of the most important goals in indoor PV design.
Since the light conditions are so different, the efficiency of indoor and outdoor solar cells cannot be directly compared. Indoor cells may show higher relative efficiency, but always under much lower light levels.
What certifications do Epishine’s indoor solar cells have?
When was Epishine founded?
Where is the Epishine team located?
Epishine’s headquarter and production are in Linköping, Sweden, with R&D located on-site to support continuous innovation. Our team includes seven PhDs and represents 17 nationalities worldwide.
Light Energy Harvesting
What is ambient light?
Ambient light is the general background light present in an environment. Indoors, it includes artificial lighting such as LED or fluorescent lamps, as well as natural daylight entering through windows and light reflected from surrounding surfaces.
Indoors, ambient light typically ranges between 50 and 500 lux, which is significantly lower than direct sunlight, which can reach around 100,000 lux.
What is energy harvesting?
Energy harvesting is the process of capturing small amounts of energy from the surrounding environment and converting it into usable electrical power. Also known as power harvesting, ambient energy harvesting, or energy scavenging. Energy harvesting enables low-power electronic devices to operate without disposable batteries or wired connections.
One common form of energy harvesting is light energy harvesting, where ambient indoor light is converted into electrical power using organic photovoltaic cells.
Read more:
What is the minimum light level required for indoor photovoltaics?
Epishine’s organic solar cells are designed to operate efficiently in extremely low light conditions, starting from just 1 lux, which is comparable to the light from a candle.
However, an indoor solar cell must generate enough power to meet the energy requirements of the device it is intended to power. This depends both on the device’s power consumption and on the available light levels in the environment. Contact us for more details on your specific application.
What is light energy harvesting?
Light energy harvesting is the process of converting light into electrical power using photovoltaic materials. In indoor applications, ambient light from sources such as LEDs and fluorescent lamps can be used to power low-energy electronic devices.
Can the indoor solar cell capture artificial light (light bulbs)?
Does the indoor solar cell need sunlight?
Where should I put my device to get enough power?
Epishine will guide you through the process to make sure you mount your product where it gets enough power. General guidelines for placement of light-powered products:
- Avoid shading from doors, furniture or other objects
- Place the product in a well-lit area
- Place the product away from direct sunlight
Typical indoor light levels:
- A bedroom or bedside lamp: around 50 lux
- A living room: 100–300 lux
- An office environment: around 500 lux
- Close to a window or in a supermarket: approximately 1,000 lux
If the cells are optimized to capture low indoor light, does that mean they generate even more electricity in direct sunlight?
Materials
What does "organic" mean in organic solar cells?
What is the semiconductor in organic photovoltaics?
What materials does the Epishine indoor cell consist of?
Epishine Indoor Solar Cells
What is photovoltaics?
What is indoor photovoltaics (IPV)?
What is the power output of Epishine indoor solar cells?
The power output depends on the light intensity.
At 500 lux, which corresponds to typical office lighting conditions, our indoor solar cells deliver up to 22 μW/cm².
For the latest performance data at different light levels, please refer to our updated datasheet.
What is the difference between Epishine OneCell and Epishine MultiCell?
Epishine's indoor solar cells are available in a selection of sizes and formats, adapted for different applications. To meet different voltage requirements, Epishine offers two product categories: Epishine OneCell and Epishine MultiCell. Both are based on the same basic technology but differ in how the voltage is adapted to the application. Each individual cell provides an output voltage of approximately 0.5 V. Epishine MultiCell uses multiple cells connected in series to achieve a higher voltage, while Epishine OneCell consists of only one coherent cell that provides a more homogeneous surface.
Depending on the application, the solar cell can also be combined with a PMIC (Power Management Integrated Circuit) for better voltage matching and energy management. This enables adaptation based on both the requirements of the electronics and the desired system architecture.
What sizes of indoor solar cells does Epishine offer?
What is the lifetime of the indoor solar cell?
How do you recycle Epishine organic photovoltaic cells?
Consult regional regulations before disposing of any electronic device or component.
If Epishine indoor solar cells are part of an electronic device, the electronic device shall be handled in accordance with applicable regional regulations for handling electronic waste.
Epishine solar cells can be recycled through energy recovery processing. While Epishine cells can in general be regarded as household waste and handled according with applicable regional regulations for handling household waste, consult regional regulations before disposing of any product.
What is the difference between indoor photovoltaics and indoor solar cells?
What are the benefits of powering electronics with ambient light?
What is a bifacial solar cell?
A bifacial indoor solar cell (indoor photovoltaic, IPV) is designed to capture light from both sides. This unique feature boosts performance by up to 80% compared to the specifications in our data sheet when illuminated from both sides.
Bifacial solar cell integration example.
What temperature range can the indoor solar cell withstand?
What humidity levels can the indoor solar cell withstand?
What is the bending radius of the indoor solar cell?
Technology
How are Epishine’s indoor solar cells manufactured using roll-to-roll?
Roll-to-roll (R2R) printing is a continuous manufacturing process, where functional layers are printed onto a flexible substrate that moves steadily from one roll to another —an approach widely used in printed flexible electronics.
Instead of producing solar cells in separate, sheet based steps, R2R enables continuous production, more like a printing press than a traditional factory line. R2R manufacturing also makes it possible to deliver the indoor solar cells on rolls, which can simplify the next steps in the customer’s integration process for light energy harvesting applications.
Why does Epishine use roll-to-roll processing?
Why is roll-to-roll manufacturing the future for indoor pv?
R2R manufacturing is ideal for meeting the high-volume demands of low-power electronics. Continuous processing reduces handling, minimizes downtime, and optimizes material usage—enabling efficient industrial-scale production with a lower manufacturing footprint.
R2R manufacturing also enables indoor solar cells to be delivered on rolls rather than individual rigid units. This simplifies logistics, storage, and automated integration into customer assembly lines, supporting efficient high-volume product manufacturing.
What is the difference between sheet-based manufacturing and roll-to-roll manufacturing?
Many indoor solar cell manufacturing methods today are sheet-based; meaning materials are processed in separate batches and stopped between steps, instead of in a continuous roll-to-roll process. Epishine has chosen roll-to-roll printing as it enables high-volume processing needed for production with strong benefits of cost and energy efficiency compared to sheet-based production methods.
With just 1 gram of active semiconductor material, Epishine can produce several square meters of solar cell surface. Compared to conventional solar manufacturing, which often requires large facilities and heavy infrastructure, Epishine’s roll-to-roll process uses a fraction of the footprint, reducing material use, energy demand, and required floor space.
What is unique about Epishine indoor solar cells?
Epishine’s indoor solar cells are designed as part of a fully integrated production system optimized for scalable indoor light energy harvesting. Key differentiators:
Advanced photonic materials
Indoor-optimized organic semiconductor materials and custom inks engineered for efficient performance capturing ambient indoor light.
Roll-to-roll printing
A high-speed, scalable manufacturing process designed for high-volume, enabling precise layer deposition and consistent quality.
Custom-built machines
Industrial equipment engineered and adapted to Epishine’s proprietary materials and process requirements for high-volume manufacturing.
Patented lamination process
A proprietary lamination method eliminating internal short-circuiting and encapsulation process, supporting volume and reliable performance in low-light indoor conditions.
What is Lux?
Integration
How does a light-powered system work?
Light is captured by the solar cell and converted into electrical power. This energy is routed through a power management unit, which regulates and optimizes the energy flow before storing it in an energy storage component.
The stored energy powers the microcontroller (uC), which manages the system. The uC communicates with the available sensors in the product, runs the device logic, and acts as the communication manager towards the outside world.
Wireless communication can be implemented in two ways, either a radio chip is integrated in the uC, or the system uses a separate radio chip. In the separate-radio setup, the uC controls what data is sent and when, and the radio chip transmits the data accordingly. The software outside the device receives the transmitted data and decides what actions to take, for example increasing heating or ventilation.
What other components are needed for a light-powered system to operate?
A light energy harvesting device is not defined by the solar cell alone. True energy autonomy is achieved when the solar cell, power management unit, energy storage, microcontroller (uC), communication and software are designed as one integrated system.
Each component plays a specific role, but long-term reliability, performance, and efficiency depend on how well these parts work together.
What electrical contacting do Epishine’s indoor solar cells have?
Epishine delivers cells with ablated patch for electrical contacting. Use an ACF (anisotropic conductive film) or a conductive adhesive to connect the solar cell directly to the PCB or to an FPC.
For support with contacting and other product integration inquiries, please contact sales@epishine.com
What radio protocols can be used with light energy harvesting?
What should be considered when designing a light energy harvesting (LEH) device?
Designing a light energy harvesting (LEH) device requires consideration of both the application requirements and how the system components work together within the available energy and application needs.
Application needs
Define how the product will be used and how often it needs to process and transmit data. These factors determine the required energy demand. Wireless communication is one of the most energy-consuming functions. Carefully consider how often data needs to be sent, as starting up the radio and transmitting data consumes significant power.
Define the system goal
Clarify whether the objective is a fully energy-autonomous system or extended battery lifetime. This will guide architecture and design decisions.
Minimize quiescent current
Reduce all continuous power consumption. Any leakage or quiescent current, components that draw power even when inactive, can significantly impact the energy needed.
Maximize time in sleep mode
Keep the system in sleep mode as much as possible. Active operation should only occur when necessary.
Optimize the system as a whole
Performance depends on how well all components—solar cell, power management, energy storage, microcontroller, and radio—work together. It is important to ensure they are well matched to the application and operating conditions.
The Epishine team will guide you in selecting and optimizing these components to ensure the system works efficiently under your specific conditions.
Applications
Can I replace the battery in my device with an indoor solar cell?
Retrofitting a battery-powered product is possible. However, systems originally designed for batteries often include unnecessary power consumption and are not optimized for low power operation.
Designing the product with light energy harvesting (LEH) in mind from the start typically results in a more efficient and better-performing product.
Which products can be powered by light energy harvesting?
Light energy harvesting enables a wide range of low-power electronics to operate using ambient indoor light.
These energy harvesting applications span multiple industries:
Consumer electronics
Self-charging remote controls (RCU), in-ear devices, keyboards, and computer mice.
Retail
Electronic shelf labels (ESL) and visual displays.
Logistics
Asset trackers and connected devices for tracking and monitoring goods.
Smart buildings / IoT
Wireless sensors, access cards, digital locks, and smoke detectors.
These applications of energy harvesting reduce the need for battery replacement and enable scalable, maintenance-free systems.