Method for designing a broadband and omnidirectional hybrid antireflection coating for organic solar cells using the quarter-wavelength rule

The reflection losses are among the principal causes that limiting the performances of the solar cells. Indeed, the conventional organic solar cell (OSC) provides a relatively low photocurrent mainly due to light reflection at the front and back sides of the glass-substrate. To overcome this limitation we propose an optimized hybrid antireflective structure. The proposed design is a combination between multilayer antireflection coating (MARC) and moth eye structure (MES). The OSC with this antireflection coating, consisting of thin coherent multilayer stack and moth eye subwavelength structure, is modeled using transfer matrix method (TMM) and effective medium theory (EMT). In this work, several antireflection coating designs with different dielectric material films are investigated. The layer thicknesses of the MARC were tuned such that they obey to quarter-quarter-quarter (Q-Q-Q) and quarter-half-quarter (Q-H-Q) wavelength rules to obtain zero reflectance. Based on these configurations, we performed an optimization algorithm to design the antireflection coating that maximizes the short circuit photocurrent density (J_SC). The optical analysis is applied to ITO/PEDOT:PSS/P3HT:PCBM/Al bulk heterojunction (BHJ) organic solar cell. The highest value of short circuit photocurrent density is obtained for OSC with hybrid MES/Glass-substrate/MARC(QHQ) antireflective structure using Al₂O₃/ZrO₂/M-optm material films. In comparison with the conventional organic solar cell without antireflection coating, the short circuit photocurrent density was improved by 5% at normal incidence. Besides, the antireflection effect is maintained even at large incidence angle of 68° thanks to the omnidirectional optical propriety of the moth eye structure.