Investigation On The Interface And Structure/performance Optimization Of Organic Solar Cells

Organic photovoltaics cells?OPVs?have attracted intensive attentions due to the advantages of low cost,good flexibility,simple preparation,aboundant material-source,and being able to roll-to-roll production,etc.At present,improving device performance,reducing production costs and achieving large-scale production are important issues for the commercialization of organic solar cells.This thesis focuses on the interface and structure/performance optimization of organic solar cells,aiming at disclosing device mechanism as well as improving device performance,which is divided into the following four parts:?1?Anode modification of OPV devices based on copper phthalocyanine:fullerene?CuPc:C60?system.In order to study the effect of anode modification on device performance,we introduced anode layer with different materials including CuPc,MoO₃,HPCzI or MoO₃ doped HPCzI in OPV devices using vaccum deposition method.Among them,HPCzI was prepared in our lab and firstly proposed as an anode buffer in OPV device by us in our previous work.Best performance was achieved with 25%MoO₃ doped HPCzI device.Energy level analysis showed that HPCzI can improve hole extraction efficiency due to the well matched hole levels.Study on the charge transport properties demonstrated that the increase of hole transport ability in MoO₃ doped HPCzI layer was partially account for the improvement of device performance.?2?Anode and cathode modification of OPV devices based on poly-3-hexylthiophene:[6,6]-phenyl C61-butyric acid methyl ester?P3HT:PCBM?system.We used electrostatic spray?ES?method to prepare p-?pure P3HT?and n-?pure PCBM?modified OPV devices with different p-and n-layer thickness.It was found that the efficiencies of devices with additional p-layer or with both p-and n-layers are higher than those without p-or n-layer modification.By analyzing the charge transport properties of the corresponding layers,it turned out that the p and n layers could obviously improve the hole mobility,leading to improved device performance.?3?Gradient concentration investigation of OPV devices based on the P3HT:PCBM system.Using ES method,OPV devices with a vertical concentration gradient were fabricated.The active-layer was as such:P3HT enriched P3HT:PCBM/normal P3HT:PCBM/PCBM enriched P3HT:PCBM.The thickness of the active layer was varied in order to optimize this gradient structure.Results showed that the efficiency of the device with donor enrichment layer had significantly improved comparing to devices with other active layer structure.By studying the charge transport properties of the different structures,it was found that the hole mobilities were significantly increased when adding the donor-rich layer as well as the both donor-rich and acceptor-rich layers to devices.?4?Performanceoptimizationofpoly{4,8-bis[?2-ethylhexyl?oxy]benzo[1,2-b:4,5-b`]dithiophene-2,6-diyl-alt-3-fluoro-2-[?2-ethylhexyl?carbonyl]thieno[3,4-b]thiophene-4,6-diyl}:[6,6]-phenyl C71-butyric acid methyl ester?PTB7:PC70BM?device by varying the preparation conditions.Using ES method,the device optimum preparation conditions were obtained as follows:the concentration of active layer solution is 10 mg/ml,substrate temperature is 40 ^oC and the spray time is 5 min.And the OPV device efficiency reached 4.8%with this conditions.However,thermal annealing could evidently reduce the device performance.When 1 nm LiF was added as a cathode modification layer of the device,the efficiency increased from 4.8%to 6.6%.