Efficient and air-stable plastics-based polymer solar cells enabled by atomic layer deposition

High efficiency (up to 4.5%) and air-stability (>10000 h) of plastics-based and glass-based polymer solar cells (PSCs) with a blended poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C₆₁ butyric acid methyl ester (PCBM) active layer were achieved by the applications of atomic-layer-deposited (ALD) films for four key functions: electron collection, interface optimization, gas-permeation barrier, and thin-film encapsulation. Using a 60 nm ALD ZnO film deposited at 90 °C as the electron-collection layer (ECL), we obtained inverted PSCs with 4.1% power conversion efficiency (PCE) as well as high shunt resistance (R_sh) and low series resistance (R_s), thanks to the low carrier concentration and high electron mobility of the ALD film. Modifying the ZnO ECL's surface with a 0.6 nm ALD HfO₂ layer further improved the PCE to 4.5% as a result of enhanced electron injection and hole-blocking. The ALD ZnO ECL was also an adequate gas barrier with water vapor transmission rate (WVTR) < 5 × 10^-4 g m^-2 day^-1, eliminating the need for a dedicated gas barrier on the plastic substrates. Combining the ALD ZnO ECL with a 26 nm ALD Al₂O₃/HfO₂ nano-composite encapsulating film (WVTR < 5 × 10^-4 g m^-2 day^-1) prevented O₂/H₂O-induced degradations for the PSCs, achieving > 10000 h of storage lifetime in air. This combination of high PCE and long lifetime presents a significant improvement over current achievable results.