The Effect Of Alkanedithiols As Solvent Additives On The Performance Of Polymer Solar Cells

The work of this paper mainly focuse on improvement of the performance of solar cells based on P3HT:PC61BM blend bulk heterojunction. The approach used in this paper is mixing some high boiling point additives with Chlorobenzene in the solvent processing of active layer, aiming at improving the morphology of blend film and promoting phrase separation between donator and acceptor material. Thus an effective transportation network is fabricated in the active layer, which results in high carrier mobility and collection ratio, good performance of the devices as well. The work of this paper includes three parts. First, different amount of1,8-octanedithio (ODT) is added into the solvent in order to study the relationship between additive concentration and the performance of photovoltaic devices. Second, additives with different molecular groups in the same amount are added into the blend film, which can lead to good performance for the photovoltaic devices in varying degrees. Third, alkanedithiols with different length of alkane are added into the solvent, but not all of them can enhance the device performance. The conclusions of the work above are as follows:1. Different amount of ODT is added into the P3HT:PC61BM blend solvent. Through the I-V characteristic curve, we find none of VOC, JSC, FF and PCE enhances linearly as the amount of ODT increases. Only when the amount of ODT is60μL per mL CB, JSC and FF increase. And PCE reachs its maxmum. On the contrary, if the amount of ODT continues to increase, all these four parameters tend to decrease.2. The addition of alkane with different molecular groups aims at figuring out the relationship between molecular groups and device peformance. This work mainly takes advantage of the characteristics of different additives, such as boiling point and rate of volatilization. The results reveal that additives improve the performance of solar cells, especially the effect of DIO. The power conversion efficiency enhances as the molecular weight of groups increases.3. The last part is research about the effects of length of alkane in dithiol on performance of photovoltaic devices. The study reveals that all polarity, solubility parameter and boiling point have influences on morphology of blend film in varying degrees. In addition, the solubility parameter differences between additives and PC61BM play an important role in aggregation of PC61BM as well. Accordingly, in this case we should take the boiling points and solubility parameters of additives into consideration. This paper makes a systematic research about the effect of additives on the performance of bulk heterojunction photovoltaic devices. We make a concrete experiments and study of it in several aspects, such as concentration of additives, molecular groups and length of alkane. Last but not least, we are acknowledged with the specific function and mechanism of alkanedithiols in the polymer photovoltaic devices.