Predicting thermal stability of organic solar cells through an easy and fast capacitance measurement

Abstract

Degradation of Organic Photovoltaic (OPV) devices is currently a topic under intense research as it is one of the main limitations towards the commercialization of this technology. Morphological changes at both active layer and interfaces with the outer contacts are believed to determine main key issues to be overcome. In-line techniques are essential to rule out any effect arising during sample fabrication.Unfortunately, the number of physical techniques able to provide morphological information on complete and operational devices is certainly limited. In this work, we study the thermal degradation of bulk heterojunction (BHJ) solar cells composed by different donor polymers with techniques developed to provide in-situ information on operational devices. Capacitance measurement as a function of temperature monitors the electrical integrity of the active layer and provides the threshold temperature (T MAX ) at which the whole device becomes thermally unstable. We found a direct correlation between the threshold temperature T MAX , obtained by capacitance-temperature measurements on complete OPV devices, and the power conversion efficiency decay measured at 85°C. Devices show to be thermal stable when the temperature of the thermal stress is below the T MAX , while above the T MAX evident changes in the active layer or at the active layer/electrode interface are also detected by confocal fluorescence microscopy. The capacitance method gives precious guidelines to predict the thermal stability of BHJ solar cells using accelerated and easy tests.

Thermal Stabilization of the Bulk‐Heterojunction Morphology in Polymer:Fullerene Solar Cells Using a Bisazide Cross‐Linker

“…As a third example of a mostly amorphous polymer, we investigated PBDTT‐QFF in a bulk‐heterojunction with PC 61 BM. Similar benzodithiophene‐quinoxaline derivates were previously found to be rather stable at 85 °C and superior over PTB7:PC 61 BM solar cells. During annealing at 120 °C for 40 h, however, the performance of PBDTT‐QFF:PC 61 BM solar cells decreased to 43% (rel.…”

Toward High‐Temperature Stability of PTB7‐Based Bulk Heterojunction Solar Cells: Impact of Fullerene Size and Solvent Additive

“…[37] Interfaces between the active layer and outer contacts also play a very important role in device operation and stability as shown recently. [37,57,60] The quality of an interface is influenced by potential charge accumulation and formation of leakage current, which depends on the concentration of donor and acceptor at the contacts. [61,62] Here, we observe that leakage current is reduced after PAS-140 accompanied by an increase in V oc .…”

“…[25,27] While thermal stability of PTB7:PC 70 BM blends was not yet studied in details, device using PTB7:PC 70 BM BHJs processed with DIO show already strong losses in performance at moderate annealing temperature of 80 °C-100 °C. [37] In contrast, solar cells using PTB7:PC 70 BM blends processed without DIO are reported to possess good thermal stability at 140 °C in the range of several minutes. [38,39] Similar results were obtained for solar cells using poly [(4,8- 70 BM BHJs.…”

Thermally Stable High‐Performance Polymer Solar Cells Enabled by Interfacial Engineering

“…Ta ble 1s hows the results of this study compared with previous reports on the thermal stabilityo fP SCs. [3,4,7,9,[21][22][23] For both normala nd inverted PSC structures, the initial efficiency and long-term thermals tability of the performance werei mproved significantly in this study.…”

“…[3,4,7,9,[21][22][23] For both normala nd inverted PSC structures, the initial efficiency and long-term thermals tability of the performance werei mproved significantly in this study. [3,4,7,9,[21][22][23] For both normala nd inverted PSC structures, the initial efficiency and long-term thermals tability of the performance werei mproved significantly in this study.…”