Correlation of Changes in Electronic and Device Properties in Organic Photovoltaic with Exposure to Air

Abstract In polymer‐based organic photovoltaic cells, the capability of charge extraction/injection of molybdenum trioxide (MoO ₃ ) is demonstrated as interface layer for polymer bulk heterojunction (BHJ). The present work determines the dipole formed at the MoO ₃ and conjugated poly [2,3‐bis (3‐octyloxyphenyl) quinoxaline‐5,8‐diyl‐alt‐thiophene‐2,5‐diyl] (TQ1):(6,6)‐Phenyl C71 butyric acid methyl ester (PC ₇₁ BM) bulk heterojunction interface. This dipole has a major influence on the charge transport across the TQ1:PC ₇₁ BM interface. The formation of the dipole is determined with electron spectroscopy and the depth profiling technique neutral impact collision ion scattering spectroscopy. Metastable induced electron and UV‐photoelectron spectroscopy is applied to determine the enclosed surface coverage of minimum 1.5 nm MoO ₃ and a maximized dipole strength of 2.4 eV with >2 nm MoO ₃ deposition on BHJ. It is also demonstrated that the air exposure reduces the dipole at the interface and leads to a decrease in cell performance providing evidence that the dipole formed at the interface is beneficial for the functioning of photovoltaic cells. The results indicate that the reduction in dipole might not be the only mechanism leading to cell performance degradation. The findings of the present work have relevance for other BHJ systems because MoO ₃ as high work function material is likely to interact with other organic materials in a similar way.