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PV EXPO 2021 (March 3-5)

PV EXPO 2021 Yamagata University exhibited original organic series solar cells

March 3-5, PV EXPO 2021 was held in Tokyo Big Site. As regards solar cell device, Yamagata University exhibited original organic series solar cells.

Characteristics of perovskite solar cell is enhanced by optimization of HTL material

Yamagata University has exhibited organic film solar cell and perovskite solar cell as next generation solar cell.

The latter was firstly exhibited in this time. Its structure is original. As you know, in perovskite solar cell, layer structure and manufacturing process of dye-sensitized solar cell are diverted in general due to back of development. In this structure (Meso-porous device), a porous TiO2 is used as hole transport layer (HTL). As you can image easily, it's necessary to anneal this TiO2 at high temperature, same as 450 - 500 . For this reason, FTO (F doped SnO2) with high heat resistance is used as under transparent electrode.

On the other hand, this device is an inverted structure due to manufacturing at low temperature. It is composed of ITO transparent electrode/HTL/perovskite layer/electron transport layer (ETL) 1/ETL 2/upper metal electrode. In short, layer structure is reversed from meso-porous device. It's possible to use conventional ITO as a transparent electrode, and decrease process temperature, such as 150 and under because of TiO2 free. As a result, various plastic films with low heat resistance can be used as a substrate. Of course, wet-etching property and transmittance are excellent because of adoption of ITO.

Figure 1. Relationship of device characteristics and HTL materials

Picture 1. Perovskite solar cell

In this device, MAPbI3, C60, B4PyMPM and Ag are used as perovskite, ETL1, ETL2, and cathode respectively. And also, without and with HTL devices (PEDOT:PSS, PTAA, TFB) were pilot-produced. As figure 1, characteristics of TFB device were most, and its incident photon-to-current efficiency (IPCE) was 20.2 %. This value is almost same as that of poly-crystal Si solar cell. This is reason why grain size of spin-coated perovskite is enlarged same as 300 nm and over because of high contact angle (41) of TFB surface.

MORESCO announced to produce organic film solar cell by R2R making great use of wet process

By contrast, MORESCO has exhibited flexible organic film solar cells in Yamagata University's booth. The company is cooperating with Yamagata University in organic film solar cell. Exhibited devices were pilot-produced by Roll to Roll (R2R) process, wet-process (die coating and screen printing), and laser directly etching. In short, layers except for electrode were formed by photolithography and vacuum process-free. And also, device was solidly encapsulated by a commercial plastic film with gas barrier layer.

Picture 2. Flexible organic film solar cell
TCFside (front) Metal side (back)
16.4 V
16.0 V
246 mA 
139 mA
FF 0.56  0.55
Pmax 2.3 W 1.2 W
Vmax 11.7 V   12.1 V
Imax  190 mA  101 mA 
cell   5.1 %  2.8 %

Table 1. Typical characteristics

In the booth, green and navy devices (320~320o) were exhibited. ICPE of sample was 5.1 %. This is almost maximum value in organic film solar cell. The company is supplying sample products for the present moment, and will mass-produce the device in near future.

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