Employing Non-halogen Solvents To Process Non-fullerene Organic Solar Cells And Study Their Photovoltaic Performance

In recent years,organic photovoltaics（OPVs）have been deeply favored by scholars due to its’advantages of low cost,light weight,could be made into flexible device through solution process,compatible with large scale industrial roll-to-roll printing and so on.Lately,the reported power conversion efficiency（PCE）of single-junction bulk-heterojunction（BHJ）devices has exceeded 18%,and the efficiency of layer-by-layer（Lb L）devices made by sequential deposition way has also exceeded 17%.However,the active layer component of these high efficiency OPVs are mostly cast by chloroform（CF）,chlorobenzene（CB）,ortho-dichlorobenzene（o-DCB）and other hazardous halogen solvent,which will not only cause significant pollution to the environment,but also threat the body health of involved staff.Therefore,in order to ensure that OPV could be extensively applied in practical production,it is particularly important to utilize lower toxic non-halogen solvent as far as possible and guarantee the final devices own good stability performance.This paper contains six chapters,the introduction of this paper first briefly describes the basic concepts involved in OPV field;including OPV’development history,working mechanism,the preparation process of the device,common methods of characterization of active layer morphology,and so forth.Then,the related research progress of OPV processed from non-halogen solvent is also introduced briefly;and the following five chapters are briefly summarized as follows.A non-halogen solvent additive 1-phenylnaphthalene（1-PN）,which is less mixed with ortho-xylene（o-XY）,is utilized to process PTB7-Th:EH-IDTBR system,and final inverted device’PCE reaches 10.37%.Compared with the pure o-XY processed device（PCE is 8.43%）,three parameters of photovoltaic performance are promoted simultaneously.Moreover,this value is slightly higher than that of pure CB processed device（PCE is 9.94%）.And the air storage stability of the devices processed by this solvent combination is better than that of devices prepared by CB.In addition,the PM6:IT-4F and PM7:IT-4F active layer materials are cast from this three solvent systems,respectively.The inverted devices’efficiency based on o-XY and 1-PN combination processing are the highest,corresponding to 12.48%and 12.29%,respectively.A low boiling point non-halogen and non-aromatic solvent carbon disulfide（CS₂）is used to process PM7:IT-4F and PM7:IT-4Cl by contrast with o-XY.Finally,the efficiency of pure CS₂processed devices are 11.72%and 12.52%,respectively,which are higher than that of o-XY processed devices（PCE are 10.93%and 10.77%,respectively）,mainly owes to the higher and more balanced carrier mobility from CS₂prepared devices.Additionally,these two sets of devices with active layer cast from CS₂present a good heating stability.A non-halogen solvent o-XY with higher boiling point used for a secondary solvent is added into the low boiling point solvent CS₂to find a suitable film drying process.Finally,efficiency of 14.70%is reached after utilizing CS₂solvent containing 3%volume fraction of o-XY to process PM7:Y6-BO-4F active layer material,which is higher than that of devices processed with only one of the solvents.In addition,the devices prepared from this solvent combination based on PM6:Y6-BO-4F and J61:Y6-BO-4F systems,corresponding to PCE of15.24%and 13.29%,respectively.A less reported non-halogen solvent Indan is applied to PTQ10/Y6 active layer,while small molecular Y6 is processed by CF due to its’limited solubility.Eventually,the efficiency of inverted Lb L devices prepared by Indan/CF is 15.36%,which is higher than that of devices processed by CF/CF with PCE of 14.93%.Additionally,the Indan/CF solvent combination can also be applied to PM6/Y6 based Lb L devices,and efficiency reaches 14.99%,higher than that of CF/CF processed devices with PCE of 14.43%.A Lb L type photoactive layer cast from whole non-halogen solvents is explored.Polymer donor PTQ10 is still selected and Indan is used as solvent,and acceptor Y6-BO-4F with longer side chain than Y6 can be dissolved in non-halogen solvent tetraphydrofuran（THF）.Adding small amount of mesitylene（MES）into THF as non-halogen solvent additive can improve device photovoltaic performance.Eventually,the efficiency of PTQ10/Y6-BO-4F inverted Lb L devices processed by Indan/THF+3%MES reaches 14.95%,higher than that of BHJ devices processed by CF+0.5%DIO with PCE of 14.24%.Meanwhile,the highest efficiency among the inverted Lb L devices processed from non-halogen solvent is achieved.