Simultaneous enhancement of light absorption and improved charge collection in PTB7-Th: PC 70 BM organic solar cells
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Simultaneous enhancement of light absorption and improved charge collection in PTB7-Th: PC70BM organic solar cells a,
Kunal Borse 1, Ramakant Sharma
a,1
a,
a,
, Dipti Gupta * and Aswani Yella *
a
Department of Metallurgical Engineering and Materials Science, Indian Institute of Technology Bombay, Powai, Mumbai- 400076, India *Corresponding Author E-mail: [email protected] (D.G), [email protected] (A.Y) 1 Kunal Borse and Ramakant Sharma contributed equally to this work. ABSTRACT Enhancing the light absorption and improving the charge collection are considered as two major prerequisite for achieving highly efficient bulk heterojunction organic solar cells (BHJ OSCs). In the present study, we have explored Ga doped ZnO as an electron transport layer for improving the charge collection in one of the promising donor: acceptor system comprised of Poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b;4,5-b']dithiophene-2,6diyl-alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4-b]thiophene-)-2-carboxylate-2-6-diyl)] (PTB7Th):phenyl-C71-butyric acid methyl ester (PC70BM). With the inverted geometry having a configuration of ITO/GZO (40nm)/PTB7-Th: PC70BM (100nm)/MoO3 (10nm)/Ag (100nm), maximum power conversion efficiency (PCE) of 7.24% has been achieved, while it is limited at 6.89% for devices with undoped ZnO.It was found that PCE can be further improved to 8.35 % after V-grooved textured PDMS films were attached to the backside of OSC substrates. We attribute this performance enhancement in OSCs is due to increased total optical path length of the incident light within the device. INTRODUCTION Although power conversion efficiency (PCE) for solution processed bulk heterojunction organic solar cells (OSCs) is way behind the other emerging PV technologies, they have attracted a significant attention owing to the many advantages such as good cost-efficiency balance, short energy payback time and unique form-factor.1, 2 Enhancing the light absorption and improving the charge collection are considered as two major prerequisite for achieving highly efficient bulk heterojunction OSCs. Previous studies have suggested that device and interfacing engineering is challenging yet cheaper way for enhancing the light absorption and improving the charge collection when compared to designing and developing new donor and/or acceptor molecules. Over the years, use of different combinations of electron and/or hole transport layers, solvent additives, incorporation of metal, dielectric and/or semiconducting nanoparticles (NPs), etc.in active layer have evolved as some of the traditional approaches of device engineering. Sandwiching active layer between different combinations of electron and/or hole transport layers and/or using different solvent additives is less challenging and guarantees the enhancement in device performance due to improved charge collection.3 But incorporation of metal, dielectric and/or semiconducting nanoparticles (NPs), which does help in enhancing the light absorption, is tricky as it has many problems associated wi
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