(A) study on the device architecture of semi-transparent, film-type perovskite solar cells

Abstract

With the increasing awareness of environment pollution and energy crisis, renewable energy has been recognized as an important alternative source of energy. Especially, perovskite solar cell (psSC) technologies have recently gained immense attention as one of the most promising photovoltaic (PV) technologies because of their outstanding optoelectronic properties. We here explore strategies to realize flexible and/or semi-transparent psSCs so that they can have features not readily available to conventional solar cells. To this end, $CH_3NH_3PbI_3$ ($MAPbI_3$)-based psSCs are developed in which a $TiO_2$ layer is replaced with a layer of C60 evaporated onto indium tin oxide layers covered with polyethylenimine ethoxylated (PEIE) layers. Unlike $TiO_2$ layers requiring a high-temperature sintering, $C_60$ is deposited while the substrate is held at room temperature, making it compatible with various plastic substrates for flexible psSCs. The PEIE layers are shown to play key roles, not only as an electron collecting interfacial layer but also as a surface modifier that helps maintain the integrity of the $C_60$ layers during spin-coating of the perovskite active layers. Using the proposed device architecture, we demonstrate flexible psSCs that exhibit high power conversion efficiency with low hysteresis.

The proposed technology is then combined with soft vacuum-laminated top transparent electrodes to realize film-type semi-transparent (ST) psSCs. The flexible top transparent electrode based on thin metal is realized and optimized on the polydimethylsiloxane (PDMS) film, which has much lower Young’s modulus than most conventional plastics. Using an optimal buffer layer that combines conducting polymers called ‘PEDOT:PSS’ and D-sorbitol as an adhesion promoter, film-type ST-psSCs are successfully demonstrated that can be bent at a radius of curvature down to a few mm and exhibit power conversion efficiency of 10%. We believe the proposed method can be advantageous in that the top electrode can be prepared separately and later combined seamlessly with the roll-to-roll, solution-processed solar cells and is conformable to a rather thick structure, which is relevant to fabrication of modules in psSCs.