| Mesoscopic solar cells (MSCs) are one of the most promising third-generation photovoltaic technologies due to its simple fabrication process, wide raw material sources, and low price advantages. In MSCs, mesoporous nanocrystalline with high specific surface area are used as charge collection layer, dyes (Dye-sensitized solar cells, DSSCs) and organic-inorganic hybrid perovskite (Perovskite solar cells, PVSCs) are used as light harvesting layer, where the work electrode interface consisted of mesoporous nanocrystalline and light-absorber have significant influence on the photovoltaic performance. To date, the reported power conversion efficiency (PCE) of DSSCs have reached 13.0%. The exceptional optoelectronic properties make hybrid halide perovskite materials ideal for PVSCs that stepped from DSSCs. To date, the certificated power conversion efficiency (PCE) of PVSCs have reached 21.0%, which is comparable to the PCE of best CIGS and CdTe thin film solar cells.Traditional MSCs (n-type MSCs) usually are based on a mesoporous n-type semiconductor/light-absorber as work electrode. Recently, p-type MSCs with a mesoporous p-type semiconductor/light-absorber as work electrode become attractive due to their potential to construct high-efficiency pn tandem cells with n-type MSCs through molecular engineering of light-harvesting materials. This pn tandem cells possesses a theoretical efficiency limitation well beyond that of single-junction MSCs. However, low photocurrent densities from state-of-the-art p-type MSCs limit output of current density of tandem cells; therefore it has become a bottleneck for the development of high efficiency tandem cells. Therefore, optimizing the power conversion efficiency of p-type MSCs is a key issue.In p-type MSCs, p-type semiconductor/light-absorber interface play an important role in photo-to-electric process. Herein, my thesis topic is focused on synthesis of p-type dyes for p-type DSSC, synthesis of p-type semicondutor for carbon electrode based pn tandem PVSCs, and systematically investigation of the influence of p-type semiconductor/light absorber interface on device performance. It is expected that this study set up important experimental and theoretical basis for the development of high-performance MSCs. The main contents of this thesis are listed as following:Three organic dyes zzx-opl, zzx-op2 and zzx-op3 with carboxyl group functionalized diphenylamine as electron donors,9,9-dihexyl-fluorene as linker, and perylene-imide as electron acceptors were designed and synthesized for p-type DSSCs. It was found that when the linker changed from a single fluorene to the combination with 3,4-ethylenedioxythiophene and thiophene units, the absorption maximum gradually shifted to the longer wavelengths, but the energy conversion efficiency decreased from 0.184,0.160, to 0.153%. Photophysical and electrochemical characterization were performed to study difference originated from different charge injection quantum yield, which was 90.3,53.9, and 39.0% for zzx-op1, zzx-op2, and zzx-op3, respectively. We further found that insertion of electron-rich heterocyclic aromatic groups 3,4-ethylenedioxythiophene and thiophene lifted the HOMO energy levels and decreased the driving forces for the hole injection. It is likely that?0.80 eV of hole injection driving force is needed to achieve relatively high hole injection quantum yield for NiO based p-type DSSCs.One or two 9,9-dihexyl-fluorene were introduced into zzx-op1 to obtain zzx-op1-2 and zzx-opl-3. Time-resolved fluorescence decays measurement showed that three dyes were energetically favorable for efficient hole injection. The dark current and electrochemical impedance measurements revealed that the zzx-opl and zzx-opl-2 sensitized cells exhibited smaller dark current densities than that of the zzx-opl-3 sensitized cell. Transient photovoltage/photocurrent decay measurements showed longer electron lifetime in zzx-opl-2 sensitized solar cells. All results indicated that the dye zzx-opl-2 formed a much more compact dye block layer to retarding the charge recombination between the injected hole in the NiO film and the hole acceptor in the electrolyte. The zzx-opl-2 based p-type DSSCs achieved an unprecedented photocurrent density of 7.57 mA/cm2 with a power conversion efficiency (PCE) of 0.357% under AM 1.5G conditions.Inspired by pn tandem DSSCs, we replaced the ZrO2 insulator layer in the state-of-the-art TiO2/ZrO2/carbon(perovskite) PVSCs with mesoscopic p-type NiO particles layer led to 39% increase of energy conversion efficiency. In these cells, the light absorber, CH3NH3PbI3, formed instantly inside the pores of the entire TiO2/NiO/carbon layer upon sequential deposition of PbI2 and CH3NH3I. Photoluminescence, impedance spectroscopy and transient photovoltage decay measurements have revealed that introduction of NiO extended the electron lifetime and augmented the hole extraction of the counter electrode. As a result, the photocurrent and open-circuit voltage both increased, resulting in a cell with impressive energy conversion efficiency of 11.4% under AM1.5G conditions.By introducing another mesoporous ZrO2 insulator layer between mesoporous TiO2 layer and NiO layers, we fabricated perovskite solar cells with TiO2/ZrO2/NiO/carbon(perovskite) structure, where the ZrO2 insulator layer retard the direct contact of TiO2 layer and NiO layer to avoid charge recombination. Impedance spectroscopy results clearly show charge accumulation at the interface of perovskite. The NiO is believed to efficiently accelerate charge extraction to the external circuit and retard charge recombination. As a result, the device possesses an appreciated power conversion efficiency of 14.5% under AM 1.5G illumination.Highly crystalline NiO nanosheets were synthesized as top hole transport layers in perovskite solar cells with TiO2/ZrO2/NiO/carbon(perovskite) structure. Time-resolved photoluminescence decay measurements, electron impedance spectroscopy and transient photovoltage decay measurements have revealed that the NiO nanosheets as top hole transporters exhibit superior charge collection efficiency and a prolonged charge lifetime, which was attributed to better charge collection properties and large pore for perovskite pore filling and crystal growth. As a result, an impressive power conversion efficiency of 14.2% is achieved under standard testing conditions. |
PDF Full Text Request