There are several methods for the evaluation of the performance of solar cells through the voltage loss. However, the advantages and disadvantages of each method have not been thoroughly discussed nor elucidated. This study compares these various methods to clarify their advantages and disadvantages. The bandgap offset W OC has been used for the evaluation of the voltage loss. However, it was found that such approach gives inaccurate assessment of the voltage loss in thin-bulk and quantum-structure solar cells. Our study discusses the reasons for such inaccuracy and proves that we can accurately evaluate the nonradiative voltage loss in quantum-structure solar cells using the optoelectronic reciprocity theorem and detailed-balance theory. Our findings enable a fair, accurate, and accessible evaluation of the nonradiative voltage loss in solar cells which facilitates the development of high-efficiency quantum-structure solar cell.