The study investigates the recombination mechanisms in polymer-fullerene bulk heterojunction (BHJ) solar cells, which significantly impact the short circuit current (Jsc) and fill factor (FF). The authors use light intensity and temperature-dependent current-voltage (IV) measurements to analyze the recombination kinetics, which evolve from first-order recombination at short circuit to bimolecular recombination at open circuit. The "missing 0.3V" observed in the open circuit voltage (Voc) is attributed to the temperature-dependent shift in quasi-Fermi levels in the polymer and fullerene domains. The results highlight the importance of reducing interfacial trap states to enhance charge extraction and improve solar cell performance. The study provides a detailed understanding of the recombination mechanisms and their impact on the power conversion efficiency (PCE) of polymer BHJ solar cells.The study investigates the recombination mechanisms in polymer-fullerene bulk heterojunction (BHJ) solar cells, which significantly impact the short circuit current (Jsc) and fill factor (FF). The authors use light intensity and temperature-dependent current-voltage (IV) measurements to analyze the recombination kinetics, which evolve from first-order recombination at short circuit to bimolecular recombination at open circuit. The "missing 0.3V" observed in the open circuit voltage (Voc) is attributed to the temperature-dependent shift in quasi-Fermi levels in the polymer and fullerene domains. The results highlight the importance of reducing interfacial trap states to enhance charge extraction and improve solar cell performance. The study provides a detailed understanding of the recombination mechanisms and their impact on the power conversion efficiency (PCE) of polymer BHJ solar cells.