Increased efficiency of low band gap polymer solar cells at elevated temperature and its origins

Authors

Bin Yang, University of Nebraska–LincolnFollow
James Cox, University of Nebraska–Lincoln
Yongbo Yuan, University of Nebraska-LincolnFollow
Fawen Guo, University of Nebraska–LincolnFollow
Jinsong Huang, University of Nebraska-LincolnFollow

Document Type

Article

Date of this Version

9-2011

Citation

APPLIED PHYSICS LETTERS 99, 133302 (2011); doi:10.1063/1.3643450

Comments

Copyright (c) 2011 American Institute of Physics. Used by permission.

Abstract

Photovoltaic characteristics of a low bandgap polymer, poly[(4,4′-bis(2-lethylhexyl)dithieno-[3,2-b:2′,3′-d]silole)-2,6-diyl-alt-(2,1,3-benzothiadiazole)-4,7-diyl], based bulk hetero-junction organic photovoltaic were investigated from room temperature (RT) to 145 °C to evaluate its applications in harsh environments. The power conversion efficiency was found to increase from 4.1% at RT to 4.5% at 105 °C with increased short circuit current density (J_sc) and fill factor (FF) despite the decreased open circuit voltage (V_oc). Detailed investigation revealed that J_sc and FF improvements were caused by the increased and balanced carrier mobilities at higher temperatures. The V_oc of the low bandgap polymer solar cell is determined not only by the energy levels and dark currents, but also by the binding energy of charge transfer excitons (CTEs). A slower reduction of V_oc is observed at high temperatures due to the decreased binding energy of CTEs.