Hunting Hidden Electricity in Crystalline Solar Cells with New Encapsulation Technique

Dr. Dipti Tamboli

(datamboli@coe.sveri.ac.in)

HoD, Electrical Engineering Department,

SVERI’s College of Engineering, Pandharpur

 

Photovoltaic is one of the promising renewable sourcesof power that has been proven over the decades tomeet the future challengeof energy needs. Organic and perovskite thin-film solar cells are an emerging cost-effective photovoltaictechnology because of low-cost manufacturing processing and their lightweight.However, in the commercial use of solar cells, it results in poor stability and electricity production loss. As aresult, the improved performance of solar cells has not been fully revealed at thepanel scale. Over the past few decades, there is a continuous development of crystalline Si solar cells from back surfacefield structures (BSF) to the passivated emitter and rear contact (PERC),interdigitated backcontact (IBC) and heterojunction intrinsic thin layer (HIT) solar cells to improve its efficiency up to 26.7%.

It is possible to extract more than 10% of ‘hidden electricity’ in crystalline solar cells using a new encapsulation process based on poly‐dimethyl siloxane (PDMS) coatings and a three-dimensional module structure. Compared to ethylene-vinyl acetate (EVA)films, the new coating is said to avoid cutting off short-wavelength light.The new process, which is based on a three-dimensional module structure, is intended to avoid the critical weaknesses of EVA films in terms of light trapping and chemical stability, such as browning problems and the cutting off of short-wavelength light.

Fig. 1 Photovoltaic solar cell

 

 

Encapsulated solar cells embedded between substrate and superstrate (back and front. sheets), glass or plastic sheets, to create compact and sealed units protected against environmental influences (oxygen and moisture), UV radiations, and converting it into visible photons. Solar cell strings are encapsulated between two sheets ofencapsulant foil.

Properties of encapsulation materials

1.       The encapsulant has to provide low light absorption and an adapted refractive index to minimize interface reflectance.

2.       A high thermal conductivity reduces operating temperatures and thus improves electric yield.

3.       For electrical safety, only very low leakage currents are allowed by IEC 61215 standard.

4.       In terms of PV module reliability, the encapsulant properties have to maintain strong adhesion to the other module components and protect the cell and metallization from external impacts UV irradiation, humidity, temperature cycles, mechanical loads, electric potential relative to the ground, etc.

5.       The material cost, processing cost, and processing time should be less with shelf life and better quality.

Different encapsulation materials and techniques were used by the researcher to test the performance and reliability

I.       Trapping short-wavelength light

The technique was tested on four types of crystalline cells including polycrystalline and monocrystalline back surface field structure (BSF) devices and PERC and interdigitated back

contact (IBC)mono cells. All the cells showed increased efficiency with the new coating for all values of angle of incidence, the researchers stated. “It is very interesting that the poly-dimethyl siloxane(PDMS) coating improves the efficiency in comparison with bare cells because it implies that the PDMS coating provides not just transmission of short-wavelength light – which is cut off by EVA encapsulation – but also induces an additional efficiency-enhanced mechanism for solar cells which was not well-known until now.”

According to the research team, efficiency enhancement for vertical illumination ranged from 1-1.5%, depending on cell type. “The short-wavelength, under-450 nm light produces more power by PDMS coating than the bare cells, regardless of the type of solar cell.”

II.    Yield increase

The scientists added anti-reflective coatings in EVA films that do not prevent the reflection of blue-colored, short-wavelength light. That light is, however, captured by the PDMS coating, according to its developers.The researchers said the increase in electricity production in polycrystalline BSF cells manufactured with the new process was around 9%, while mono BSF cells registered a 7% rise. For mono PERC and IBC cells, power yield was raised 8% and 4.5%, respectively.

The researchers claim solar modules produced with the new technique may be better suitable for urban areas, which typically feature restricted installation space and high amounts of scattered light, compared with direct and vertical illumination.

 

References:

 

1].  Yoshikawa, Kunta, et al. "Silicon heterojunction solar cell with interdigitated back contacts for a photoconversion efficiency over 26%." Nature Energy 2.5 (2017): 17032.

2].  Yun, Min Ju, et al. "Finding 10% hidden electricity in crystalline Si solar cells using PDMS coating and three‐dimensional cell arrays." Progress in Photovoltaics: Research and Applications 28.5 (2020): 372-381.

3].  Peike, Cornelia, et al. "Overview of PV module encapsulation materials." Photovoltaics International 19 (2013): 85-92.

4].  Uddin, Ashraf, et al. "Encapsulation of organic and perovskite solar cells: a review." Coatings 9.2 (2019): 65.