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Inefficient light absorption and poor charge separation are considered as two major bottlenecks for achieving highly efficient bulk heterojunction organic solar cells (BHJ OSCs). In the present study, we have introduced an additional phenyl-C71-butyric acid methyl ester (PC 70 BM) layer to modify the interface between ZnO based electron transport layer (ETL) and photoactive layer comprised of Poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b; 4,5-b′]dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4- b ]thio-phene-)-2-carb-oxylate-2-6-diyl)] (PTB7-Th):PC 70 BM. This interface engineering has quenched the electron–hole recombination at the interface and has improved power conversion efficiency (PCE) from 6.65 to 7.74%. Devices were fabricated in an inverted geometry having a structure ITO/ZnO (40 nm)/PC 70 BM (5 nm)/PTB7-Th:PC 70 BM (70 nm)/MoO 3 (10 nm)/Ag (100 nm). Additionally, V-grooved textured PDMS films were attached to the backside of OSC substrates which has further improved PCE to 9.12%. Our study suggests that the performance enhancement as observed in OSCs with V-grooved textured PDMS films could be due to increased total optical path length of the incident light within the device. [ABSTRACT FROM AUTHOR]

Ga-doped ZnO(GZO) is investigated as an electron transport layer in organic solar cells based on a promising donor: acceptor system of poly[(5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl)-alt-(3,3‴-di(2-octyldode-cyl)-2,2′; 5′,2″; -5″,2‴-quaterthio-phen-5,5‴-diyl)] (PffBT4T-2OD):phenyl-C71-butyric acid methyl ester (PC 70 BM). With the inverted geometry having a configuration of ITO/GZO (40 nm)/PffBT4T-2OD:PC 70 BM (270 nm)/MoO 3 (20 nm)/Al (100 nm), maximum power conversion efficiency (PCE) of 9.74% has been achieved, while it is limited at 8.72% for devices with undoped ZnO. Our study based on the structural, morphological, compositional, and electrical characterizations indicate that suggests enhanced device performance of the GZO-based devices resulted mainly from the improved electrical properties of Ga-ZnO thin films as compared to undoped ZnO. [ABSTRACT FROM AUTHOR]

Abstract We investigate the charge carrier dynamics of inverted organic solar cells (OSCs) based on PffBT4T-2OD: PCBM and PTB7: PCBM – the two leading systems among the OSCs based on polymer-fullerene bulk-heterojunction – to elucidate the origin of their performance difference. Transient absorption spectroscopy (TAS) and photo-electrochemical impedance spectroscopy (photo-EIS) were employed to unravel the photo-physics that govern the cell operation of these two highly efficient bulk heterojunction OSCs. While photo-EIS indicates that the two systems under study exhibit similar behavior in terms of recombination, TAS results reveal that PffBT4T-2OD: PCBM systems not only have higher charge generation rate but also more efficient charge transfer than PTB7: PCBM systems, leading to the power conversion efficiency of PffBT4T-2OD: PCBM-based OSCs (9.16%) that is higher than that of PTB7: PCBM-based OSCs (6.44%). Graphical abstract Image 1 Highlights • Charge carrier dynamics of PffBT4T-2OD: PCBM and PTB7: PCBM OSCs have been compared. • TAS and Photo-EIS measurements along with optical simulation were carried out. • Higher PCE for PffBT4T-2OD: PCBM OSCs is due to better absorption and carrier collection efficiency. [ABSTRACT FROM AUTHOR]