Experimental determination of the relationship between the elements of a back-to-back diode model for organic photovoltaic cells’ S-shaped I-V characteristics and cell structure

Elisa Sesa,Warwick J Belcher,Paul C Dastoor,Darmawati Darwis,Xiaojing Zhou

doi:10.1063/1.5063467

Elisa Sesa, Warwick J Belcher + Show 3 more

Open Access

https://doi.org/10.1063/1.5063467

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Abstract

Equivalent circuit models are becoming increasingly important for the development of large scale demonstrations of organic photovoltaics. The ‘S’ shaped profile is a common feature of OPV current-voltage (I-V) curves and consequently equivalent circuit models that replicate these features are urgently required. In this paper we prepare a case study based on ITO/PEDOT-PSS/P3HT:PCBM/Al devices whose I-V profiles transition from ‘S’ shape to ‘J’ shape with increasing aluminium thickness prepared using low evaporation rates. We show that the new back-to-back diode model (B2BDM) not only faithfully models these I-V profiles but, more importantly, that the specific circuit elements in the model directly correlate with the physical structures in OPV devices that determine the ‘S’ shaped character. On the basis of these observations, the physical interpretation of the B2BDM is discussed.

Highlights

As organic photovoltaics (OPVs) approach commercial scale production, the need for accurate equivalent circuit modelling of these systems has become more pressing
We show that the well-characterised P3HT:PCBM system provides an ideal case study for validating the B2BDM model; demonstrating definitively that the equivalent circuit elements in the B2BDM are directly correlated with real physicochemical structures within the OPV device
It is clear that the in the current-voltage (I-V) curves vary systematically from ‘S’ to ‘J’ shaped with increasing aluminium cathode thickness

Summary

Introduction

As organic photovoltaics (OPVs) approach commercial scale production, the need for accurate equivalent circuit modelling of these systems has become more pressing. In this paper we systematically change the I-V profile in OPV devices from ‘S’ to ‘J’ shaped by varying the top aluminium layer thickness and changing the degree of oxidation of the metal cathode.

Results

Conclusion