The Formation And Study Of Authigenic Buffer Layer In Organic Semiconductor Photovoltaic Materials

The many advantages of organic solar cells have make it become one of the most promising of photovoltage devices,the improvement of performance of organic solar cells is mainly focusing on materials,device structure,morphological control and interfacial engineering.The performance of devices usually inhabited by larger roughness?energy level mismatch during making progress,but the buffer layer of interfacial engineering could solve this problem well,so it has attracted much attention.Solvent treatment is the commonly effective method in interfacial engineering,which could derive conveniently composition and thickness control buffer layer,but good solvent was used in the past research.In this paper,poor solvent methanol was used to treat poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b?]dithiophe-ne-alt-3-fluorothieno[3,4-b]thiophene-2-carboxy-late](PTB7-Th)and poly[[N,N-bis(2-octyldodecyl)-napthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5?-(2,2?-bithiophene)](N2200)binary mixed active layer by soaking or solvent vapor annealing two different methods.According to the principle of polarity,there is stronger interaction between polar solvent and polar material.Polymer N2200 has a stronger interaction with methanol than PTB7-Th,so as treatment time went on,the authigenic buffer layers with different main composition formed on the surface,First,using methanol soaking active layer,we have proved the N2200 has stronger interaction with methanol than PTB7-Th by the measurement of contact angle and film thickness;what's more,with the increased of soaking time,the authigenic buffer layers with N2200 as main composition formed on the surface were found by the measurement of surface work function and surface composition,which deduced the surface work function of the active layer and the potential barrier between active layer and electrode of conventional device and realized the purpose of improving device efficiency.Second,with further increasing methanol soaking time,the authigenic buffer layers with PTB7-Th as main composition formed on the surface,which increased the surface work function of the active layer and reduced the potential barrier between active layer and electrode of inverted device and realized the purpose of improving device efficiency.Third,further studid the work mechanism of methanol to PTB7-Th / N2200 active layer by annealing treatment.When annealing time short 3 minutes,the surface work function continuing decreased because more N2200 diffuse to active layer surface and the authigenic buffer layers with N2200 as main composition formed on the surface.With the annealing time further increased,the surface work function would keep consistent and no change.This paper put forward using poor solvents to treatment active layer firstly and proved this is efficiently method to improvement device performance by experiment,at the same time,we also explored the work mechanism of methanol to PTB7-Th / N2200 active layer.