TY - JOUR
T1 - Quantifying Quasi-Fermi Level Splitting and Open-Circuit Voltage Losses in Highly Efficient Nonfullerene Organic Solar Cells
AU - Phuong, Le Quang
AU - Hosseini, Seyed Mehrdad
AU - Sandberg, Oskar J.
AU - Zou, Yingping
AU - Woo, Han Young
AU - Neher, Dieter
AU - Shoaee, Safa
N1 - Funding Information:
The authors acknowledge the Alexander von Humboldt Foundation for funding. H.Y.W. acknowledges financial support from the National Research Foundation (NRF) of Korea (2019R1A2C2085290 and 2019R1A6A1A11044070). O.J.S. acknowledges support from the Sêr Cymru Program through the European Regional Development Fund, Welsh European Funding Office, and Swansea University strategic initiative in Sustainable Advanced Materials. The authors thank Bowen Sun for partly preparing the studied devices. Open access funding enabled and organized by Projekt DEAL.
Publisher Copyright:
© 2020 The Authors. Solar RRL published by Wiley-VCH GmbH
PY - 2021/1
Y1 - 2021/1
N2 - The power conversion efficiency (PCE) of state-of-the-art organic solar cells is still limited by significant open-circuit voltage (VOC) losses, partly due to the excitonic nature of organic materials and partly due to ill-designed architectures. Thus, quantifying different contributions of the VOC losses is of importance to enable further improvements in the performance of organic solar cells. Herein, the spectroscopic and semiconductor device physics approaches are combined to identify and quantify losses from surface recombination and bulk recombination. Several state-of-the-art systems that demonstrate different VOC losses in their performance are presented. By evaluating the quasi-Fermi level splitting (QFLS) and the VOC as a function of the excitation fluence in nonfullerene-based PM6:Y6, PM6:Y11, and fullerene-based PPDT2FBT:PCBM devices with different architectures, the voltage losses due to different recombination processes occurring in the active layers, the transport layers, and at the interfaces are assessed. It is found that surface recombination at interfaces in the studied solar cells is negligible, and thus, suppressing the non-radiative recombination in the active layers is the key factor to enhance the PCE of these devices. This study provides a universal tool to explain and further improve the performance of recently demonstrated high-open-circuit-voltage organic solar cells.
AB - The power conversion efficiency (PCE) of state-of-the-art organic solar cells is still limited by significant open-circuit voltage (VOC) losses, partly due to the excitonic nature of organic materials and partly due to ill-designed architectures. Thus, quantifying different contributions of the VOC losses is of importance to enable further improvements in the performance of organic solar cells. Herein, the spectroscopic and semiconductor device physics approaches are combined to identify and quantify losses from surface recombination and bulk recombination. Several state-of-the-art systems that demonstrate different VOC losses in their performance are presented. By evaluating the quasi-Fermi level splitting (QFLS) and the VOC as a function of the excitation fluence in nonfullerene-based PM6:Y6, PM6:Y11, and fullerene-based PPDT2FBT:PCBM devices with different architectures, the voltage losses due to different recombination processes occurring in the active layers, the transport layers, and at the interfaces are assessed. It is found that surface recombination at interfaces in the studied solar cells is negligible, and thus, suppressing the non-radiative recombination in the active layers is the key factor to enhance the PCE of these devices. This study provides a universal tool to explain and further improve the performance of recently demonstrated high-open-circuit-voltage organic solar cells.
KW - nonfullerene acceptors
KW - organic solar cells
KW - quasi-Fermi level splitting
KW - quasi-steady-state photoinduced absorptions
KW - surface recombinations
KW - voltage losses
UR - http://www.scopus.com/inward/record.url?scp=85096722815&partnerID=8YFLogxK
U2 - 10.1002/solr.202000649
DO - 10.1002/solr.202000649
M3 - Article
AN - SCOPUS:85096722815
VL - 5
JO - Solar RRL
JF - Solar RRL
SN - 2367-198X
IS - 1
M1 - 2000649
ER -