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

High efficiency (up to 4.5%) and air-stability (> 10 000 h) of plastics-based and glass-based polymer solar cells (PSCs) with a blended poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C-61 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 degrees 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 x 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 x 10(-4) g m(-2) day(-1)) prevented O-2/H2O-induced degradations for the PSCs, achieving > 10 000 h of storage lifetime in air. This combination of high PCE and long lifetime presents a significant improvement over current achievable results.