{'fraction_non_alphanumeric': 0.02947845804988662, 'fraction_numerical': 0.007558578987150416, 'mean_word_length': 4.781659388646288, '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}}
Improving quantum efficiency in organic solar cells with a small energetic driving force

Organic solar cells based on a polymer donor (PM7) and a non-fullerene acceptor (Y5) with a very small energetic difference between the local excited state and the charge transfer (CT) state are investigated. We find that the small energetic difference (ΔECT) leads to a low voltage loss (0.44 eV). However, the short-circuit current density (Jsc) of the solar cell based on PM7:Y5 is very low, due to monomolecular recombination of the CT state excitons, limiting the internal quantum efficiency of the device. To solve the problem with the inefficient exciton dissociation, a polymer donor (PBDB-T) with a similar chemical structure to PM7 is employed as a second donor component for constructing ternary solar cells. We find that the frontier energy levels of the two donors are hybridized, allowing us to realize fine-tuning of the effective energy of the CT state and ΔECT of the ternary blend, by varying the PBDB-T content. As a result, a significantly improved CT state dissociation efficiency is achieved by adding a small amount of PBDB-T in the active layer. Meanwhile, the low voltage loss property of PM7:Y5 is very well maintained in the ternary solar cell, due to the energy level hybridization of the donor materials.