Studies On Morphology,Stability And Performance Of The Novel Thin-film Solar Cells

This work is focused on the morphology, stability and performance of the novel thin-film solar cells. The main contents of dissertation include three parts.1、The solvent vapors of THT, THN, DEGDE, and DCB, with different boiling points, vapor pressure and different solubility parameters of P3HT and PCBM, were used to treat the poly(3,4-ethylenedioxylenethiophene):poly(styrenesulphonic acid)(PEDOT:PSS) layers for improving the morphology of active layers and the power conversion efficiency (PCE) of the devices.(?) The device treated with the DEGDE-vapor shows the best performance, which can attribute to the characteristics of DEGDE, low vapor pressure and low solubility of PCBM. Solvent-vapor-treated devices show the optimum morphology with low surface roughness, suitable crystallization of P3HT and clear phase separation with PCBM.(?) The results of XPS show that DEGDE treatment can drive the P3HT and PCBM toward anode and cathode respectively, forming the ideal vertical composition distribution for improving carrier transportation.(?) The investigation on the film composition at the active layer/anode interface reveals that PCBM enriched on the bottom surface lead to the low Voc and FF, which is in accord with the results of solvent-vapor-treatment.2-. The effects of photo-induced defects and thermal degradation on inverted polymer solar cells (PSCs) based on the blends of PBDTTT-C and PC70BM were investigated.(?) The ideality factor was used to analyze the effects of photo-induced defects on PSCs. The results show that the dominant trap states increase with increasing illumination time, which indicates defect-induced recombination at the internal donor/acceptor interface and the electrode interfaces will lead to the decrease in the Voc and Jsc, and the degradation of device performance.(?) The differential scanning calorimetry (DSC) measurement reveals that the temperature of phase transition of PBDTTT-C:PC70BM blend is about64℃, which is much lower than their individual temperature of phase transitions. The J-V curves of heated devices display a steep decline when the temperature is beyond70℃. The investigations on the optoelectronic behaviors and the morphology of heated devices reveal that the more compact distribution of the donor-acceptor phases and the decreased interface areas between the doner and acceptor, with the increase of heating time, lead to unfavorable exciton dissociation, pathway for charge-carrier transport, and finally sustaining decrease in Jsc.3、A solution-processed perovskite solar cell with organolead trihalide perovskite materials(CH3NH3PbI3) as the absorbing layer, improved PCE by optimizing the parameters of the electron transfer layers and the thickness of perovskite films. The possible origins of anomalous hysteresis in the J-V curves were identified by investigating the ideally factor.(?) The PCE of the perovskite solar cell reaches to13%, by using the uniformity and smooth ZnO-NPs film as the the electron transfer layer and an optimized thickness absorbing layer.(?) The linear relation of Jsc on light intensity in a double logarithmic scale with a slope close to1, indicates that no substantial space charge build-up in the perovskite device, charge carrier losses in the absorbing layer are dominated by monomolecular recombination via defects and bimolecular recombination is a rather minor loss. The ideality factors under different scan directions are extracted from the dependence of Voc on illumination intensity and dark J-V curves. The obtained ideality factor is close to2under forward scan, which indicates that the more carrier recombination comes from the trap-assisted recombination, compared with the reverse scan.(?) The dependence of Voc on the light intensity reveals that ideality factor under forward scan (from high to low light intensity) is1.73, while decreases to1.59under reverse scan, which indicated that more defect-assisted recombination via electron traps is existed in the forward-scan-process.