Abstract
The operation and the design of organic solar cells with donor/acceptor heterojunction structure and exciton blocking layer is outlined and results of their initial development and assessment are reported. Under halogen lamp illumination with 100 mW/cm2 incident optical power density, the devices exhibits an open circuit voltage VOC = 0.45 V, a short circuit current density JSC between 2 and 2.5 mA/cm2 with a fill factor FF ≈ 50%, an external quantum efficiency (electrons/s over incident photons/s) EQE ≈ 5% and a power conversion efficiency of about 0.5%. Measurements of the photoelectrical characteristics with time are also reported, confirming that non encapsulated organic solar cells have limited stability in ambient atmosphere.
Highlights
Organic amorphous semiconductors in the form of polymers or oligomers have made their way in Electronics and Optoelectronics [1]
Organic solar cells (SCs) with improved structures and materials, including bulk heterojunction [5] and perovskites [6], have reached power conversion efficiencies above 10% [7] but stability and lifetime is still an issue even with encapsulated devices [8]. In this contribution we report the design, initial development and assessment of donor (D)/acceptor (A) heterojunction SCs
The difference in energy between the lowest unoccupied molecular orbital (LUMO) of A and the highest occupied molecular orbital (HOMO) of D must be smaller than the Frenkel exciton energy to ensure an ideally 100% probability of charge transfer (CT) exciton formation at the D-A interface with subsequent charge separation by the internal electric field
Summary
Organic amorphous semiconductors in the form of polymers or oligomers ( called small molecules) have made their way in Electronics and Optoelectronics [1]. The difference in energy between the LUMO of A and the HOMO of D must be smaller than the Frenkel exciton energy to ensure an ideally 100% probability of CT exciton formation at the D-A interface with subsequent charge separation by the internal electric field. This is believed to occur, even in this three-layer case, through allow electrons energy states below the LUMO energy level created in the EBL by damage during the metal cathode deposition [11,12].
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