Design of a Flexible Thin-Film Encapsulant with Sandwich Structures of Perhydropolysilazane Layers.

Perovskite solar cells (PSCs) have attracted considerable attention due to their excellent photovoltaic properties, but stability issues have prevented their widespread application. PSCs must be protected by encapsulation to extend their lifetime. Here, we show that perhydropolysilazane (PHPS)-based multilayered encapsulation improves the lifetime of PSCs. The PSCs were encapsulated by converting PHPS into silica under vacuum ultraviolet (UV) irradiation. The PHPS-based multilayer encapsulation method achieved a sandwich structure of PHPS/poly(ethylene terephthalate) (PET)/PHPS with a water vapor transmission rate (WVTR) of 0.92 × 10-3 gm-2 d-1 (at 37.8 °C and 100% relative humidity). We then performed a reservoir test of the encapsulated PSCs to confirm the moisture stability of the encapsulation based on PHPS/PET/PHPS barrier films. The cell lifetime remained stable even after 1000 h of ambient-temperature operation. Finally, we analyzed the mechanical flexibility of the PHPS/PET/PHPS multibarrier through bending tests. The multibarrier exhibited high mechanical stability with no large increase in WVTR after bending.

A Novel Approach for the Development of Moisture Encapsulation Poly(vinyl alcohol-co-ethylene) for Perovskite Solar Cells.

In this study, we developed the universal encapsulation method using poly(vinyl alcohol-co-ethylene) (EVOH) to improve the water stability of perovskite solar cells. In order to enhance the moisture barrier property, we utilized SiO2 and graphene oxide (GO) fillers in the EVOH matrix. First, UV-treated SiO2 increased the dispersibility in the EVOH matrix and made the penetrating path more complicated, which led to a better moisture barrier property. The water vapor transmission ratio (WVTR) is enhanced from 4.72 × 10-2 (EVOH only) to 1.55 × 10-2 (EVOH with SiO2 filler) g/m2 day. Second, we found that GO reduce the unreacted hydroxyl groups that could attract water molecules at the surface of EVOH. The addition of GO increased the WVTR up to 3.34 × 10-3 g/m2 day. Finally, our EVOH-based film successfully encapsulated without the efficiency drop. The encapsulated devices surprisingly maintained 86% of their performance even under direct contact with water for 5 h.

Development of moisture-proof polydimethylsiloxane/aluminum oxide film and stability improvement of perovskite solar cells using the film.

A method for enhancing the moisture barrier property of polydimethylsiloxane (PDMS) polymer films is proposed. This is achieved by filling the PDMS free volume with aluminum oxide (AlO x ). To deposit AlO x inside PDMS, thermal atomic layer deposition (ALD) is employed. The PDMS/AlO x film thus produced has a 30 nm AlO x layer on the surface. Its water vapor transmission rate (WVTR) is 5.1 × 10-3 g m-2 d-1 at 45 °C and 65% relative humidity (RH). The activation energy of permeability with the PDMS/AlO x film for moisture permeation is determined to be 35.5 kJ mol-1. To investigate the moisture barrier capability of the PDMS/AlO x layer, (FAPbI3)0.85(MAPbBr3)0.15/spiro-OMeTAD/Au perovskite solar cells are fabricated, and encapsulated by the PDMS/AlO x film. To minimize the thermal damage to solar cells during ALD, AlO x deposition is performed at 95 °C. The solar cells exposed to 45 °C-65% RH for 300 h demonstrate less than a 5% drop in the power-conversion efficiency.