# POSS Polyimide Composite Sealed Triple‐Junction GaAs Thin‐Film Solar Cell for Long‐Term Low Earth Orbit Serve

## TL;DR

A new POSS polyimide composite is developed to protect solar cells in space from atomic oxygen and UV exposure, maintaining performance for up to eight years.

## Contribution

A POSS polyimide composite with ultrathin oxide and UV absorbent is introduced to achieve near-zero mass loss and high solar cell efficiency in low Earth orbit.

## Key findings

- The POSS polyimide composite achieves ≈0 wt% mass loss after eight years of atomic oxygen exposure.
- The solar cell maintains 23.38% efficiency at end of life after long-term atomic oxygen exposure.
- Ultrathin oxide and UV absorbent improve transmittance and resistance to degradation.

## Abstract

Polyhedral oligomeric silsesquioxane (POSS) polyimide is promising for sealing flexible photoelectronic devices for space applications. However, atomic oxygen interaction with POSS polyimide results in a porous SiOx passivating layer, ultraviolet interaction results in bonding degradation, both causing the transmittance decrease in the visible light range. In this study, the atomic oxygen exposure‐induced transmittance decrease of POSS polyimide is explained and simulated by Rayleigh scattering. Ultrathin oxide films and ultraviolet absorbent are introduced to POSS polyimide by surface‐ and bulk‐phase modifications to improve atomic oxygen and ultraviolet resistance, which achieves ≈0 wt% mass loss upon an eight‐year long‐term atomic oxygen exposure and is deduced by molecular dynamics. The atomic oxygen exposure effect on the sheet resistance of flexible conductive indium tin oxide‐POSS polyimide is explained by band structure calculation. The SiO2‐POSS polyimide sealed triple‐junction GaAs thin‐film solar cell exhibits beginning of life (BOL) and end of life (EOL) efficiencies of 27.67% and 23.38% upon an eight‐year long‐term to atomic oxygen. The atomic oxygen reactions with polyimide‐based films are explained by zero‐ and first‐order reactions, and predictive formulas are created for the film mass loss and sealed solar cell performance under the long‐term atomic oxygen exposure. This study suggests a POSS polyimide composite as a packaging film for flexible photoelectronic devices in low Earth orbit.

Ultrathin oxide layer and ultraviolet absorbent are introduced into polyhedral oligomeric silsesquioxane (POSS) polyimide to improve the transmittance conservation and realize near zero mass loss against ultraviolet and atomic oxygen exposures. The POSS polyimide composite sealed triple‐junction GaAs thin‐film solar cell exhibits enhanced endurance of atomic oxygen and thermal cycling for long‐term low Earth orbit service.