Solar Cell Short-Circuit Current Density Jsc(IV) and Integral Short-Circuit Current Density Jsc(EQE) Accurate Measurement and Comparison 01Key to Publish in PV Flagship-Journal
In December 2020, Science Magazine published the perovskite/Si tandem solar cell of Helmholtz-Zentrum Berlin (HZB), Germany, with a certified efficiency of 29.15%. This news exploded the entire photovoltaic society! This efficiency not only exceeds the 28% efficiency record of Oxford PV company in the UK, but also represents an important step towards 30% in photovoltaic technology.
We observed three important keys publishing breakthrough-efficiency in flagship-journals in the past five-years. They are:
- Provide third-party efficiency certification
- Provide the comparison difference (<5%) between Jsc(IV) and Jsc(EQE)
- Provide efficiency statistics histogram chart
The paper which HZB published in the Science also meets these three requirements. The comparison difference between Jsc(IV) and Jsc(EQE) in the article is also less than 5%. Why it is important?
This article will introduce the pain points and history of accurate measurement in the past 10 years. It will also describe that why to compare Jsc(IV) and Jsc(EQE) is vital in the present solar cell research and how to measure Jsc(IV) and Jsc(EQE) accurately.
Content
History of the initiative to accurate PV efficiency measurement
OSC has been focusing on this issue since 2006. With the development of OLED, organic solar cell (OSC) also began to receive attentions after 2005. In 2006, the OSC efficiency of the P3HT:PCBM system exceeded 4.7% which drived the development of this field. The importance of accurate measurement of PCE (Power Conversion Efficiency) has gradually been recognized by everyone with the growth of research interest. In 2006, UCLA and NREL jointly published the OSC precision measurement method in the journal Advanced Functional Materials, which is the first article to systematically discuss the precise measurement of OSC. Important concepts such as calibration of solar simulators, selection of reference cells, and correction of spectral mismatch errors are proposed.
Figure 1: UCLA and NREL published the first systematically studying paper about accurate measurement and characterization of organic solar cells in 2006.（https://onlinelibrary.wiley.com/doi/abs/10.1002/adfm.200600489）
PSC is also in the spotlight for precise measurements. Perovskite solar cells (PSCs) emerged around 2010 and have developed at an alarming rate. High PCE has brought more research investment in this field. Due to the hysteresis effect, the problem of precise measurement of perovskite solar cells has attracted more attention.
PV research community advocates for the accurate measurement. In 2014, Nature magazine published three articles in a row to advocate the importance of the accurate PCE measurement in perovskite solar cells. The viewpoint of its initiative is that both PSC perovskite solar cells and OSC organic solar cells have great potential for large-scale commercialization. However, erroneous reports of PCE efficiency will mislead the direction of the development and delay the way to large-scale commercialization.
Figure 2: In 2014, the Nature published three articles advocating the importance of the accurate PCE measurement.
In 2015, Nature Group released “A Solar Checklist”. To avoid the publication of incorrect results, which would affect the reputation of the journal and the development of the field, Nature Group released the self-checklist, requiring authors of all journals that submit their manuscripts to follow the requirements on the self-checklist. The self-check form mainly requires the authors to describe in details about the relevant conditions for testing solar cells in their own laboratories. The main purpose is to ensure the reproducibility of the published data.
Figure 3: “A Solar Checklist” published by Nature Group in 2015. It requires authors need to fill in and submit this information at the same time during the submission stage to help improve the reproducibility and transparency of the paper results in the PV research field.
In 2020, Cell Press released “PV Checklist”. In September 2020, Joule’s, an journal in the energy field under Cell Press, the impact factor soared from 15.04 in 2019 to 27.05. It was promoted to the top flagship journal in the energy field. It is required to submit the PV Checklist when submitting the manuscripts in solar cell research fields. The requirements of this document are more rigorous than the “Solar Checklist” of Nurture Group in 2015. It needs to provide more comprehensive test condition information. At the same time, the requirements and concepts of calibration traceability are also added. Enlitech has now provided relevant response information for our system’s users, helping customers to quickly and accurately provide all the information required on the form. If necessary, you can write to us for related information (PV Checklist; qeservice@enli.com.tw).
Figure 4: Cell Press released “PV Checklist” in 2020. It needs to provide more comprehensive test condition information. At the same time, the requirements and concepts of calibration traceability are also added.
3 keys for publishing breakthrough efficiency in PV flagship-journal
The accuracy and reliability of solar cell PCE data is the key to whether it can be published in top energy journals. We observed the data of relevant papers published in the past five years and found that there are three important trends in whether important research results can be published in top journals:
1. Provide third-party efficiency certification
2. Provide the comparison difference (<5%) between Jsc(IV) and Jsc(EQE)
3. Provide efficiency statistics histogram chart
If we check the paper that HZB published in Science in 2020, it also meets these three requirements. It provides:
- The third-party efficiency certification of Fraunhofer ISE in Germany
- The comparison difference between Jsc(IV) and Jsc(EQE) < 5%
- Efficiency statistics histogram chart
Figure 5: HZB published in Science in 2020, the perovskite solar cell with nearly 30% conversion efficiency, the Jsc(IV) and Jsc(EQE) data provided in the text. It shows that the comparison data of the two, again, is a necessary condition for publication.
The high efficiency and accurate measurement results of HZB are also shown in the comparison error of Jsc(IV) and Jsc(EQE) within 5%. In this article, we will introduce the past pain points, the key to the accurate measurement, related solutions, and the introduction of successful cases.
Pain points of the accurate measurement in the past
Breakthrough PCE data in the past are difficult to be reproduced. Fifteen years ago, in the early stage of the development of organic solar cell OSC and perovskite solar cell PSC, many breakthroughs in PCE efficiency were reported, but there are many results that are difficult to be reproduced by other research laboratories in the same field. Leaving aside moral doubts or suspicions of fraud, this phenomenon highlights the lack of knowledge and appropriate equipments and methods for accurate solar cell measurements in the entire solar cell research community at that time.
With the study of these irreproducible results, there is a growing understanding of how to properly evaluate and measure solar cells and the associated appropriate equipment. Dissertation research always precedes international testing standards. With the maturity and development of relevant research, these correct testing methods and equipment will form testing standards and gain international recognition. The IEC 60904 series developed by the International Electrotechnical Commission for terrestrial photovoltaic test standards is a prime example. This series of standards includes:
- Method of IV testing (IEC 60904-1)
- Packaging requirements for solar reference cells (IEC 60904-2)
- Definition of standard solar spectrum (IEC 60904-3)
- Traceability in the field of photovoltaic testing (IEC 60904-4)
- Temperature coefficient correction method for open circuit voltage of photovoltaic cells (IEC 60904-5)
- Correction of spectral mismatch (IEC 60904-7)
- Methods and apparatus for measuring spectral response (IEC 60904-8)
- Classification standard for solar simulators (IEC 60904-9)
From methods to equipment, after 15 years of collective efforts of the photovoltaic community, continuous re-editing and improvement of the content of these standard, it has now been able to provide the entire photovoltaic community with an accurate measurement methodology to be relied on.
Why to compare Jsc(IV) and Jsc(EQE), how to accurately measure Jsc(IV) and Jsc(EQE), and the introduction of the successful case comparison, It will be described in the next article: Solar cell short-circuit current density Jsc(IV) and integral short-circuit current density Jsc(EQE) accurate measurement and comparison 02. The outlines are as below:
Solar cell short-circuit current density Jsc(IV) and integral short-circuit current density Jsc(EQE) accurate measurement and comparison-02
– Why the comparison between Jsc(IV) and Jsc(EQE) are required
－There are still a lot of potential human errors in IV testing
－The uncertainty of Jsc(EQE) is low, which can be used to verify the Jsc(IV) of IV testing results
－Comparison error range between Jsc(IV) and Jsc(EQE)
– How to accurately measure Jsc(IV) and Jsc(EQE)
－Successful case (1) 23.32% world efficiency perovskite solar cell in 2019
－Successful case (2) 16% high-efficiency organic solar cells in 2019
－Jsc(IV) accurate measuring method
－Jsc(EQE) accurate measuring method
Lack of knowledge about accurate solar cell measurement
Lack of suitable equipment and methods
