Modeling the Effect of Annealing and Regioregularity on Electron and Hole Transport Characteristics of Bulk Heterojuncti
- PDF / 164,650 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 8 Downloads / 235 Views
1270-HH14-56
Modeling the Effect of Annealing and Regioregularity on Electron and Hole Transport Characteristics of Bulk Heterojunction Organic Photovoltaic Devices Shabnam Shambayati1 , Bobak Gholamkhass2 , Soheil Ebadian1 , Steven Holdcroft2 , and Peyman Servati1 1 Electrical and Computer Engineering Department, University of British Columbia, Vancouver, BC V6T 1Z4, Canada 2 Department of Chemistry, Simon Fraser University, Burnaby, BC V5A 1S6, Canada ABSTRACT In this study, the dark current-voltage characteristics of electron-only and hole-only poly(3-hexyl thiophene) (P3HT):[6,6]-phenyl C61 -butyric acid methyl ester (PCBM) as a function of regioregularity (RR) and annealing time is investigated using the mobility edge (ME) model. This model is used to analyze the degradation of electron and hole mobilities as a function of annealing time for 93%-RR and 98%-RR P3HT:PCBM devices. The hole mobility is almost unchanged by the RR nature of P3HT and thermal annealing. The electron mobility, however, behaves differently after annealing. The electron mobility of 98%-RR devices, which is initially higher than that of the 93%-RR devices, experiences a steep decline with annealing. Based on ME analysis, this is due to an increase in trap states in the exponential tail caused by phase segregation of solid state blends of 98%-RR polymer and PCBM. The electron mobility of 93%-RR devices increases with annealing due to an optimization of nano-phase separated morphology. INTRODUCTION In recent years, organic photovoltaic (OPV) devices have shown significant potential for use as low cost, lightweight and flexible solar cells. Many different OPV structures have been investigated; the most promising candidate is bulk heterojunction (BHJ) solar cells, namely, BHJs based on poly(3-hexyl thiophene) (P3HT):[6,6]-phenyl C61 butyric acid methyl ester (PCBM) blends [1]. The electron-donating polymer and electron-accepting fullerene constituents form a nanometer-sized binary network, referred to as a “donor-acceptor (D-A) BHJ”. Photogenerated excitons are dissociated into free charge carriers at the junction between the P3HT and PCBM interpenetrating networks, and the bi-continuity of the network provides separate pathways for hole and electron transportation to their respective electrodes [2]. The photocurrent of the OPV devices is influenced by several parameters, most significantly light absorption, charge transport, and charge separation efficiency. One of the most important limiting factors for these solar cells is mobility [3]. It has been shown that mobility can be improved by optimizing the morphology of the P3HT:PCBM networks and the molecular packing [4]. One method of achieving an optimum morphology is through increasing the degree of regioregularity (RR); regioregularity is the percentage of monomers in the head-to-tail configuration rather than head-to-head [3]. Photocurrent has been shown to increase through improved crystallinity of the polymer as a result of a higher RR [3]. The initial enhancement in performance with in
Data Loading...
