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The lifetime of a device depends highly on that of its battery. In order to enhance the longevity of microsystems or sensor networks, it is necessary for these devices to be self‐powered. Indoor photovoltaics allow the possibility of harvesting artificial light sources for powering microsystems. Whereas indoor photovoltaics based on single active layers have showed high efficiencies under LED lighting, tandem structures have yet to be tested extensively. In our study, we use finite‐difference time‐domain simulations to study the highest possible short‐circuit current density that can be extracted from tandem organic devices. We compare the simulation results to the results for photovoltaic devices based on single bulk active layer heterojunctions. Our simulations found that although detailed balanced band gap calculations show tandem photovoltaics to be viable, the low‐intensity emission spectra of white LED light sources can be better harvested by single active layer‐based photovoltaics. The current‐matching limitation of a tandem photovoltaic structure connected in series limits the highest output current and open‐circuit voltage of the device and, thus, its performance for the illumination of lower intensity light.

A bulk heterojunction (BHJ) consisting of more than one donor/acceptor is one plausible way to improve the charge transport and/or the spectral absorption range in organic solar cells. Ternary and quaternary solar cells have shown promise in this regard. However, quaternary structures have not yet been intensively tested under indoor lighting conditions. A finite-difference time-domain (FDTD)-based simulation was used to solve for the electric field intensity distribution inside a quaternary photovoltaic device illuminated by 500 lx indoor white light emitting diodes (LEDs). We found that quaternary indoor photovoltaics (IPVs) showed peculiarly high oscillations in the simulated ideal short-circuit current density (Jsc,ideal). Here, we simulated the electric field intensity inside the photovoltaic, compared it to single BHJ photovoltaics, and deduced that the electric field intensity inside the active layer of the IPV was highly sensitive to its thickness due to interference between the incident light and the light reflecting from the back electrode. We also found that Poly[N-9′-hepta-decanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT) acted as the primary light absorber in the quaternary blend while poly({4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl}{3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl}) (PTB7) acted primarily as a cascade energy level and secondarily as a supplementary light absorber.

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Conventional solar cells are predominately designed similar to a stacked structure. Optimizing the layer thicknesses in this stack structure is crucial to extract the best efficiency of the solar cell. The commonplace method used in optimization simulations, such as for optimizing the optical spacer layers' thicknesses, is the parameter sweep. Our experiments show that the introduction of genetic algorithm based method results in a significantly faster and accurate search method when compared to brute-force parameter sweep method in both single and multi-layer optimization. While other sweep methods can also outperform the brute-force method, they do not consistently exhibit 100% accuracy in the optimized results like our genetic algorithm. Our best case scenario was observed to utilize 57.9% less simulations than brute-force method. 1

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