The Study Of The Interface Regulation And Device Performance Of Organic Solar Cells

Organic solar cells(OSCs) are potential candidates for the new generation of photovoltaic industry because their advantages of low cost,lightweight,flexibility,and ease of large area fabrication through roll-to-roll pr inting.High power conversion efficiency(PCE)and excellent stability of OSCs are critical to the commercialization and practical application.Through the tireless efforts of scientists,the PCE for single junction OSCs has exceeded 12%.Besides new materials design and morphology optimization of the photoactive layer,the study of interfacial modification between active layer and electrode has become a hot topic.This paper is about the key issue of interfacial modification of OSCs,focus ing on the ionic organic materials and devices performance.An ionic small molecule based on non-conjugated structure is proposed as a new organic interlayer,leading to a h igh efficiency of 9.69%.Also,the mechanism of the recombination of the device is analyzed to explain its excellent performance.In addition,through changing the test method we studied the hysteresis of the devices with ionic inter layer.The influence of the kinds and number of ions on the PCE and hysteresis of devices is further explored.The main contents are as follows:1.A simple and commercial non-conjugated small molecule electrolyte(SME),ethylene diamine tetraacetic acid tetrasodium(EDTA-4Na),is adopted as the cathode interlayer of OSCs.The work function of ITO electrode is well adjusted and the recombination at the interface is reduced,leading to a high efficiency of 9.69%,which is the maximum PCE of the inverted OSCs based on non-conjugated SMEs.More importantly,EDTA-4Na tremendously alleviates the hysteresis phenomenon(that is,the behavior of device under external bias)happening in organic optoelectronic devices based on ionized interlayer.2.Based on our previous work,we find that EDTA derivatives with different cations exhibit different device efficiency and hysteresis.To clear up the relationship between the cations and device performance,we fabricate devices with EDTA-n H(4-n)Na(n=0,1,2,4)interlayers.As a result,we found that with the increase in the number of H~+,the device PCE decreases,and the device hysteresis increases.We speculate that,it is due to the H migration under external electrical field leads to the carboxyl rearrangement at the interface,which causes the improvement of the device performance.