A Versatile Approach to Organic Photovoltaics Evaluation Using White Light Pulse and Microwave Conductivity

Abstract

State-of-the-art low band gap conjugated polymers have been investigated for application in organic photovoltaic cells (OPVs) to achieve efficient conversion of the wide spectrum of sunlight into electricity. A remarkable improvement in power conversion efficiency (PCE) has been achieved through the use of innovative materials and device structures. However, a reliable technique for the rapid screening of the materials and processes is a prerequisite toward faster development in this area. Here we report the realization of such a versatile evaluation technique for bulk heterojunction OPVs by the combination of time-resolved microwave conductivity (TRMC) and submicrosecond white light pulse from a Xe-flash lamp. Xe-flash TRMC allows examination of the OPV active layer without requiring fabrication of the actual device. The transient photoconductivity maxima, involving information on generation efficiency, mobility, and lifetime of charge carriers in four well-known low band gap polymers blended with phenyl-C(61)-butyric acid methyl ester (PCBM), were confirmed to universally correlate with the PCE divided by the open circuit voltage (PCE/V(oc)), offering a facile way to predict photovoltaic performance without device fabrication.

Benzobisthiazole as Weak Donor for Improved Photovoltaic Performance: Microwave Conductivity Technique Assisted Molecular Engineering

“…As shown in Figure a, 8phgr; Σ μ max of PBBTzBT‐HD increased by three times compared with those of PBBTzCz, PBBTz‐ ran ‐TPD, and PBBTz‐ ran ‐BT. Interestingly, PBBTzBT‐HD exhibited two peaks at PC 61 BM = 20 and 67 wt%, which has been also observed for typical conjugated polymers such as P3HT, poly[ N ‐9''‐hepta‐decanyl‐2,7‐carbazole‐ alt ‐5,5‐(4',7'‐di‐2‐thienyl‐2',1',3'‐benzothiadiazole)] (PCDTBT), and poly[2,6‐(4,4‐bis‐(2‐ethylhexyl)‐4 H ‐cyclopenta[2,1‐ b ;3,4‐ b ']dithiophene)‐ alt ‐4,7(2,1,3‐benzothiadiazole)] (PCPDTBT) . This is due to an interplay of hole mobility, electron mobility, and their photogeneration yield at different p/n blend ratio.…”

A Hybrid Organogel of a Low Band Gap Diketopyrrolopyrrole with PC71BM: Phase Separated Morphology and Enhanced Photoconductivity

“…Upon suitable excitation, the transient photoconductivity maximum of a donor/acceptor system can be quantified from the φΣμ max values, obtained from FP‐TRMC, where φ and Σμ are charge carrier generation quantum yield upon photoexcitation and the sum of charge carrier mobilities, respectively. Photovoltaic performance of an organic semiconductor can be predicted by plotting transient photoconductivity ( Δσ max ) versus different blending ratio of donor/acceptor even without fabricating a device . Δσ max carries information about photoconductivity along with charge carrier lifetime, local charge carrier mobility, and charge carrier density.…”

On the role of local charge carrier mobility in the charge separation mechanism of organic photovoltaics

“…One of the noteworthy aspects of laser-flash TRMC is a good correlation with the device performance of BHJ manifolds, even though it is a contactless evaluation. 24,25 In addition, the use of Xe-flash TRMC with a long (10 ms) pseudo-sunlight pulse results in improved correlation between the photoconductivity maxima (Ds max ) and PCE divided by the open circuit voltage (V oc ) with four low-bandgap polymers, 26 PCDTBT, PCPDTBT, PBDTTT-CF, and PBDTTPD. The improved correlation enabled elucidation of the primary factor governing the overall device performance.…”