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 (Rsh) and low series resistance (Rs), 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.