The Organic Solar Cells Based On Tunable Sensitization And Size Of ZnO Hybrid Structure Of Electron Transport Layer

The bulk heterojunction(BHJ) organic photovoltaics(OPVs) with an active layer composited of conjugated polymer as the donor and fullerene derivative as the acceptor haveattracted great attention for low-cost energy harvesting, which areenvisioned to exhibit advantages such as their ease of fabrication, low cost, possibility for high throughput solution-processable fabrication techniques and compatibility for large area and flexible plastic substrate. In recent years, the power conversion efficiency(PCE) of single solar cell has been dramatically improved and already reached over 10%, which has been reached the requirement of commercial production. The advantages of organic solar cells make us to find new ways to improve the PCE and stability of the device, including designing new semiconducting light-absorbing conjugated polymer donor materials, controlling the photoactive layer morphology, optimization and tailored of device architectures and interface engineering for devices, and so on. In our manuscript, we focus on designing and synthesizing different ZnO nanostructure materials, and used as the electron transport layer of the inverted organic solar cells, for significantly improving the PCE and the stability of the devices.Tunable size ZnO nanoarrays(NAs) sensitized with CdS, Ag2 S, CdS/Ag2 S quantum dots and solution processed 2-(2-(2-methoxyethoxy) ethoxy) ethyl undec-10-enyl malonate(EEMC) fullerenes have been developedas electron transportlayer for improving polymer solar cellsperformance. ZnO NAs could provide direct and ordered electron channels for electron transportation, the optimized thickness of ZnO NAs was determined by means of contrast experiments with P3HT:PC61BM active layer. CdS, Ag2 S shell and CdS/Ag2 S double-shells could passivate the surface defects of ZnO NAs, increase the electron mobility and enhance light absorption. Besides, EEMC assist the infiltration of active layer into inorganic nanoarrays. Consequently, the performance of the inverted device based on thieno[3,4-b]-thiophene/benzodithiophene(PTB7)?[6,6]-phenyl C71-butyric acid methyl ester(PC71BM) with ZnO/CdS/Ag2S/EEMC core/multi-shells NAs as electron transportlayer has been greatly improved to 7.7% with a high short-circuit current density of 17.9 mA/cm2.Highly uniform one-dimensional ZnO nanoarrays(ZnO NAs) fabricated by hydrothermal process were successfully explored as electron transport layer(ETL) for offering a directand efficient path for electron transport in inverted polymer solar cells(PSCs). The inorganic CdS shell layer by in situ growthon the ZnO NAs surface was used to passivate and repair the surface defects of ZnO NAs. To further engineer the ZnO surface and improve the compatibility between ETL of inorganic ZnO/CdS core/shell and polymer blend contact junction, those organic molecules of 3,6,7,10,11-pentakis-(hexyloxy)-2-hydroxytriphenylene(TP-OH), 1-pyrenol(Py-OH) and 4'-(7-hydroxy-heptanoyl)-biphenyl-4-carbonitrile(BP-OH) were respectively spin-coated on the ZnO NAs/CdS surface to fabricate ETL based on ZnO/CdS/TP-OH NAs, ZnO/CdS/Py-OH NAs, ZnO/CdS/BP-OH NAs. The ?-? interactionsbetween the organic molecules and fullerene acceptors could lead to the well-organizeddistribution of active layer materials, which is in favor ofthe enhancement of electron selectivity and thereduction of recombination probability of electrons and holes. The incorporation of ZnO/CdS/Py-OH NAs as ETL into the inverted PSCs based on P3HT:PC61BM resulted in a superior power conversion efficiency(PCE) of 4.2% with enhanced short circuit current(Jsc) and fill factor(FF), compared to 3.1% for bare ZnO NAs, due to the intermolecular close-stacking and relative stronger?-?interaction energy between Py-OH and fullerenes. In addition, the sensitized ZnO surface led to intimate interface between ETL and active layer, which would be in favor ofincreasing the stability of the device.The solution-processed ZnO electron transport layers(ETLs) of the inverted polymer solar cells leads to various surface defects,which act as interfacial recombination centers for photogenerated charges and thereby degrade the device performance. Thethree-dimensional(3D) CdS with different morphologies, such as flower-like CdS(F-CdS), branched CdS(B-Cd S) and spherical CdS(S-CdS), are synthesized to modify ZnO ETLs, which effectively remove the intragap states of the ZnO nanocrystal films by forming Zn O/F-CdS, ZnO/B-CdS, and ZnO/S-CdS composite ETLs, respectively. Moreover, Zn O/CdS possess higher electron mobility and provide larger interface between ETL and active layer, which is beneficial for enhancing the power conversion efficiency(PCE) of the inverted organic solar cells. Especially, the device based on Zn O/S-CdS ETL and thieno[3,4-b]-thiophene/benzodithiophene(PTB7):[6,6]-phenyl-C71-butyric acid methyl ester(PC71BM) active layer achieves PCE of 8.0% with better long-term stability.