Organic solar cell photoelectric conversion efficiency testing determines the power conversion efficiency (PCE), open-circuit voltage, short-circuit current density, and fill factor of organic photovoltaic (OPV) devices under standardized AM1.5G illumination (1000 W/m², 25 °C). Accurate and reproducible characterization—performed by accredited third-party laboratories in accordance with the IEC 60904 series, ASTM E948 and related standards—is essential for verifying research results, certifying record efficiencies for publication, and qualifying commercial OPV products. This article explains the sample types, measured parameters, test methods, and quality requirements behind reliable OPV efficiency measurement.
Technical Overview
Organic solar cells (OSCs), also referred to as organic photovoltaic (OPV) devices, convert sunlight into electricity using conjugated polymers and small-molecule organic semiconductors as the light-absorbing layer. Because the active layer is typically only 100–200 nm thick and can be deposited from solution, OSCs offer distinctive advantages such as light weight, mechanical flexibility, semi-transparency, and low-cost printing on flexible substrates. These same characteristics, however, introduce measurement challenges that are more demanding than those of conventional crystalline silicon photovoltaics.
Photoelectric conversion efficiency, more commonly termed power conversion efficiency (PCE), is the defining figure of merit of an OPV device. It is calculated from three independently measured quantities according to the following relationship:
PCE (%) = (Jsc × Voc × FF) / Pin × 100%
- Voc — open-circuit voltage (V)
- Jsc — short-circuit current density (mA/cm²)
- FF — fill factor, defined as (Vmp × Jmp) / (Voc × Jsc)
- Pin — incident optical power, standardized at 100 mW/cm² (1000 W/m²)
Reliable PCE determination therefore depends on the accuracy of each individual parameter, the calibration of the light source, a clearly defined device area, and control of temperature and device stability during the test. Several factors make OPV testing particularly demanding: the narrow absorption bands of organic absorbers amplify spectral mismatch errors with solar simulators; lateral charge collection through transparent electrodes can inflate Jsc if the aperture area is not properly defined; unencapsulated devices degrade rapidly in oxygen and moisture; and device efficiency may drift under continuous illumination due to burn-in or light-soaking effects. Professional efficiency testing follows the IEC 60904 series, complemented by ASTM E948, ASTM E1021, ASTM E927, the JIS C 8910 series, and the GB/T 6495 series, and record efficiencies claimed in scientific publications are increasingly verified by accredited third-party laboratories with fully traceable calibration chains.
Testing Samples
Efficiency testing services accept a range of organic photovoltaic device formats, from small research pixels to full printed modules. Sample type, structure, and preparation directly affect the validity of the reported efficiency.
Small-Area Laboratory Cells
Typical research devices consist of a glass/ITO transparent electrode, a hole-transport layer, a bulk-heterojunction active layer based on a donor–acceptor blend (for example PM6:Y6 or PTB7-Th:PC71BM systems), an electron-transport layer, and a metal top electrode. Nominal active areas range from 0.04 to 0.26 cm², often with several independent pixels patterned on a single substrate. These devices may be tested encapsulated in ambient conditions or unencapsulated inside a nitrogen-filled glovebox.
Flexible Organic Solar Cells and Printed Modules
Devices fabricated on PET or PEN foils by blade coating, slot-die coating, or roll-to-roll printing are tested both as individual cells and as monolithic modules containing series-interconnected subcells defined by P1/P2/P3 scribing lines. For modules, each pixel and the complete module are measured to quantify area-scaling losses, series resistance from interconnects, and coating uniformity.
Semi-Transparent and Tandem Devices
Semi-transparent OSCs require the average visible transmittance (AVT) to be reported alongside PCE, since the optical window reduces photocurrent generation. Tandem (multi-junction) OSCs require spectrally selective bias illumination and voltage biasing during EQE measurement in order to resolve the contribution of each sub-cell and determine current-matching conditions.
Sample Preparation and Submission Requirements
- Active area clearly defined and documented; aperture masks supplied by the laboratory or by the customer
- Encapsulation provided for any testing performed in ambient atmosphere; packaging that protects devices from oxygen, moisture, and thermal stress during shipping
- Electrodes and contact pads labeled, with the full device stack and layer thicknesses disclosed
- A statistically meaningful number of replicate pixels submitted (typically five or more per condition)
- Clean contact surfaces free of residue, accessible to four-wire probing fixtures
Testing Items
A complete efficiency characterization typically includes the following measured and derived quantities:
- Power conversion efficiency (PCE, %) — the headline performance metric
- Open-circuit voltage (Voc, V)
- Short-circuit current density (Jsc, mA/cm²)
- Fill factor (FF, %)
- Maximum power point parameters (Vmp, Jmp) and output power density (mW/cm²)
- Complete illuminated J–V characteristics and dark J–V curves
- External quantum efficiency (EQE/IPCE) spectrum over the 300–1100 nm range, or extended to longer wavelengths for narrow-bandgap acceptor systems
- Jsc calculated by integration of the EQE spectrum with the AM1.5G photon flux, cross-validated against the J–V measured value
- Stabilized power output (SPO) under maximum power point tracking
- Forward and reverse voltage sweep comparison to quantify hysteresis or scan-rate effects
- Series resistance and shunt resistance extracted from J–V analysis
- Light-soaking or burn-in transient behavior, and T80 lifetime indicators following ISOS stability protocols
- Average visible transmittance (AVT) for semi-transparent devices
Testing Methods
Standard Test Conditions and Solar Simulator Requirements
All efficiency measurements are performed at standard test conditions (STC): the AM1.5G reference spectrum, 1000 W/m² irradiance, and a device temperature of 25 °C, as specified in IEC 60904-1 and IEC 60904-3. Solar simulators are classified in accordance with IEC 60904-9 on the basis of spectral match, spatial non-uniformity of irradiance, and temporal instability, with Class A or A+ performance required for certification-grade testing. Because organic active layers absorb predominantly in the 600–1000 nm region, the simulator spectrum must be verified across an extended wavelength range, and reference cells with spectral filtering are often employed to improve the match to the device response.
Irradiance Calibration and Traceability
The simulator intensity is set using a calibrated reference solar device whose calibration is traceable to national metrology institutes, in accordance with IEC 60904-2 and IEC 60904-4. The spectral mismatch between the simulator, the AM1.5G reference spectrum, the reference cell, and the device under test is quantified and corrected following IEC 60904-7. This step is critical for OPV devices, where mismatch errors of several percent relative can arise if left uncorrected.
J–V Measurement Procedure
- Device temperature stabilized at 25 ± 1 °C on a temperature-controlled stage, with temperature verified per IEC 60904-5
- Four-wire (Kelvin) contacting to eliminate lead and probe resistance from the measurement
- An aperture mask slightly smaller than the active area applied to prevent photocurrent collection outside the defined area, which otherwise inflates Jsc in small-area pixels
- Voltage swept from reverse bias to beyond Voc at controlled scan rates (typically 10–200 mV/s) in both directions
- Defined light-soaking and illumination history before data recording, following the laboratory procedure or agreed ISOS practice
- Unencapsulated samples tested inside a nitrogen glovebox; encapsulated samples tested in ambient laboratory conditions
EQE (IPCE) Measurement
The external quantum efficiency is measured with chopped monochromatic light, calibrated against certified silicon and indium gallium arsenide photodiodes, typically using lock-in detection. The Jsc under AM1.5G is obtained by convolving the EQE spectrum with the standard photon flux and compared with the value from the J–V sweep; agreement within approximately 5% confirms the validity of the efficiency determination. EQE measurement follows IEC 60904-8 and ASTM E1021, with bias light and voltage bias applied for tandem device characterization.
Stabilized Power Output and Maximum Power Point Tracking
Because OPV performance can drift under continuous illumination, certification-grade testing includes maximum power point (MPP) tracking over a defined period. The stabilized PCE is reported alongside the sweep-derived PCE, and any burn-in loss is quantified. This distinction is important for translating laboratory records into realistic operating performance.
Stability and Lifetime Evaluation
Extended reliability programs follow the internationally recognized ISOS protocols, including dark storage (ISOS-D), outdoor exposure (ISOS-O), laboratory light soaking (ISOS-L), thermal cycling (ISOS-T), and UV exposure (ISOS-LT) variants. Commonly reported metrics include T80 (time to 80% of initial performance), burn-in degradation, and performance at elevated operating temperature. Module-level qualification may reference adapted IEC 61215 and IEC 61730 test sequences for design qualification and safety.
Uncertainty and Quality Assurance
Accredited third-party laboratories operate under ISO/IEC 17025 quality management systems and report a full measurement uncertainty budget covering reference cell calibration, spectral mismatch correction, simulator uniformity and stability, temperature control, area definition, and instrument accuracy. Interlaboratory round-robin comparisons are used to validate measurement traceability and reproducibility across the OPV research community.
Applications
- Materials research and development: screening new donor polymers, non-fullerene acceptors, and interfacial layers against benchmark device performance
- Record efficiency certification: independent verification by accredited third-party laboratories for high-impact journal publication, with single-junction OSC efficiencies now exceeding 19%
- Pilot production and quality control: pixel statistics, yield analysis, and uniformity mapping for slot-die and roll-to-roll printed modules
- Product development for building-integrated photovoltaics (BIPV), greenhouse and agricultural films, wearable electronics, automotive integration, and indoor power for IoT devices, where testing under LED and fluorescent illuminants at 200–1000 lux is performed in addition to AM1.5G characterization
- Reliability engineering: T80 lifetime data and accelerated aging results supporting warranty models and product design decisions
- Technology benchmarking: standardized interlaboratory comparisons that enable fair comparison of device architectures and processing routes
FAQ
What is photoelectric conversion efficiency in organic solar cells?
It is the ratio of the maximum electrical output power of the device to the incident optical power, calculated as PCE = (Jsc × Voc × FF) / Pin. Under standard test conditions with AM1.5G illumination at 100 mW/cm², this metric defines what fraction of sunlight the organic solar cell converts into usable electrical energy.
Which standards apply to organic solar cell efficiency testing?
The primary framework is the IEC 60904 series, covering J–V measurement (Part 1), reference cells (Part 2), measurement principles and the reference spectrum (Part 3), calibration traceability (Part 4), temperature determination (Part 5), spectral mismatch correction (Part 7), spectral responsivity (Part 8), and solar simulator classification (Part 9). These are complemented by ASTM E948, ASTM E1021, ASTM E927, JIS C 8910, and the GB/T 6495 series, while laboratory competence is demonstrated under ISO/IEC 17025.
Why do certified efficiencies sometimes differ from laboratory-reported values?
Differences typically arise from spectral mismatch of the solar simulator, uncorrected illumination intensity, ambiguous active area definition, device degradation between measurement and verification, and transient light-soaking effects. Certified laboratories eliminate these influences through traceable reference cells, EQE cross-validation of Jsc, aperture masking, controlled temperature, and documented uncertainty budgets.
Why is an aperture mask required for small-area devices?
Transparent conducting electrodes can laterally collect photogenerated charges from regions outside the intended active area, artificially inflating the short-circuit current density of small pixels. An opaque aperture mask defines the illuminated area unambiguously and ensures that the reported Jsc and PCE correspond to a physically meaningful device area.
What is the difference between sweep PCE and stabilized PCE?
Sweep PCE is extracted from a single fast voltage scan, while stabilized PCE is measured by holding the device at its maximum power point until the output reaches steady state. For OPV devices exhibiting burn-in or transient behavior, the stabilized value is the more trustworthy indicator of real-world performance.
How are tandem and semi-transparent organic solar cells tested?
Tandem devices require EQE measurements with spectrally selective bias light and applied voltage bias to isolate each sub-cell and verify current matching. Semi-transparent devices are characterized for average visible transmittance using UV–Vis spectrophotometry, and the PCE is reported together with the transmittance value so that the efficiency–transparency trade-off can be evaluated.
What should be considered when submitting samples for third-party efficiency testing?
Devices should be encapsulated for ambient testing or clearly flagged for glovebox measurement, the active area and device structure should be documented, a sufficient number of replicate pixels should be provided, and shipping should protect the samples from oxygen, moisture, heat, and mechanical stress. Communicating any known light-soaking or measurement-protocol requirements in advance helps ensure representative results.
