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Evaluation of Built‐In Potential and Loss Mechanisms at Contacts in Organic Solar Cells: Device Model Parameterization, Validation, and Prediction
Author(s) -
Liu Bo,
Png RuiQi,
Tan JunKai,
Ho Peter K. H.
Publication year - 2014
Publication title -
advanced energy materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 10.08
H-Index - 220
eISSN - 1614-6840
pISSN - 1614-6832
DOI - 10.1002/aenm.201200972
Subject(s) - materials science , organic solar cell , absorption (acoustics) , open circuit voltage , photovoltaic system , solar cell , acceptor , photoactive layer , optoelectronics , energy conversion efficiency , short circuit , refractive index , quantum efficiency , polymer solar cell , voltage , polymer , composite material , ecology , physics , quantum mechanics , biology , condensed matter physics
Maximizing the power conversion efficiency of organic solar cells requires the simultaneous optimization of its short‐circuit current density, fill factor, and open‐circuit voltage V oc . Several key parameters of the device model needed to understand these quantities have not been reliably determined, even for the prototypical poly(3‐hexylthiophene):phenyl‐C 61 ‐methylbutyric ester (P3HT:PCBM) photoactive layer (PAL). Detailed analysis of the loss mechanisms at contacts and their rational optimization have not been possible. Here, using crosslinked P3HT network:PCBM cells with predefined ultrafine donor–acceptor morphology and very high internal quantum efficiencies, the built‐in potential V bi is measured to decouple and reliably extract other key parameters of the cells. Using the refined device parameters, the general optimization of organic solar cells is evaluated and the following is established: i) The PAL composition of the first optical absorption optimum is displaced towards the more strongly absorbing component due to thin film effects. ii) The optimal cell configuration is the one in which the slower carrier travels on average the shorter distance to the collection contact, a consequence of the asymmetric photogeneration profile. iii) The absorption thickness optima follows a simple λ p / n PAL scaling law, where λ p is its absorption center wavelength and n PAL is the corresponding refractive index.