Organic solar cells (OSCs) harvesting indoor light are highly promising for emerging technologies, such as internet of things. Herein, the photovoltaic performance of PTB7-Th:PC71 BM solar cells constructed using "optimized (with 1,8-diiodooctane (DIO))" and "non-optimized (without DIO)" processing conditions are compared for indoor and outdoor applications. We find that in comparison to the "optimized" solar cell, the "non-optimized" solar cell is less efficient under simulated solar light illumination (100 mW cm-2 , spectral range 350-1100 nm), owing to significant bimolecular charge carrier recombination losses. However, under simulated indoor illumination (3.28 mW cm-2 , spectral range 400-700 nm), bimolecular recombination losses are effective suppressed, thus the power conversion efficiency of the solar cell without DIO was increased to 14.7 %, higher than that of the solar cell with DIO (14.2 %). These results suggest that the common strategy used to optimize the OSCs could be undesired for indoor OSCs. We demonstrate that the efforts for realizing the desired "morphology" of the active layer for the outdoor OSCs may be unnecessary for indoor OSCs, allowing us to realize high-efficiency indoor OSCs using a non-halogenated solvent.
Keywords: bimolecular recombination; device optimization; energy conversion; morphology; organic solar cells.
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