{'fraction_non_alphanumeric': 0.03222748815165877, 'fraction_numerical': 0.008530805687203791, 'mean_word_length': 4.866666666666666, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Atomic Pathways Underlying Light-Induced Changes in Organic Solar Cell Materials

We identify atomic pathways, involving local O and H motion, which underlie intrinsic light-induced changes of organic materials, utilizing ab initio simulations. Light exposure generates prolonged intrinsic degradation of organic solar cells, when moisture and oxygen are absent. We consider the polymer PTB7, common for higher efficiency cells. Local motion of O from the C–O–C bridge to a C═O bond in the aromatic backbone, creates a C-dangling bond defect, with an energy of 2.1 eV. The energy barrier of ≤2.65 eV can be surmounted with blue photons. Local H motion from βC to αC within the alkyl, also generates a C-dangling bond, a similar rebonding of bridging-O, and cleaving of PTB7. Bridging O creates instability. Defect energies are lowered by ∼0.5 eV by excited electronic states. Defects can anneal reversibly or irreversibly to distorted configurations. We identify why certain organic materials are more stable, and pathways to design more stable materials.