Solid-state dye-sensitized solar cells (ssDSSCs) and recently developed perovskite solar cells (PSCs) have attracted a great attention in the scientific field of photovoltaics due to their low cost, absence of solvent, simple fabrication and promising power conversion efficiency (PCE). In these types of solar cell, the dye molecule or the perovskite can harvest the light on the basis of electron excitation. Afterwards, the electron and hole are collected at the charge transport materials. Photoelectrochemical polymerization (PEP) is employed in this thesis to synthesize conducting polymer hole transport materials (HTMs) for ssDSSCs. We have for the first time developed aqueous PEP in comparison with the conventional organic PEP with acetonitrile as solvent. This water-based PEP could potentially provide a low-cost, environmental-friendly method for efficient deposition of polymer HTM for ssDSSCs. In addition, new and simple precursors have been tested with PEP method. The effects of dye molecules on the PEP were also systematically studied, and we found that (a) the bulky structure of dye is of key importance for blocking the interfacial charge recombination; and (b) the matching of the energy levels between the dye and the precursor plays a key role in determining the kinetics of the PEP process. In PSCs, the HTM layer is crucial for efficient charge collection and its long term stability. We have studied different series of new molecular HTMs in order to understand fundamentally the influence of alkyl chains, molecular energy levels, and molecular geometry of the HTM on the photovoltaic performance. We have identified several important factors of the HTMs for efficient PSCs, including high uniformity of the HTM capping layer, perovskite-HTM energy level matching, good HTM solubility, and high conductivity. These factors affect interfacial hole injection, hole transport, and charge recombination in PSCs. By systematical optimization, a promising PCE of 19.8% has been achieved by employing a new HTM H11. We believe that this work could provide important guidance for the future development of new and efficient HTMs for PSCs.

The solid-state mesoscopic solar cells (sMSCs) have been developed as a promising alternative technology to the conventional photovoltaics. However, the device performance suffers from the low hole-mobilities and the incomplete pore filling of the hole transport materials (HTMs) into the mesoporous electrodes. A variety of HTMs and different preparation methods have been studied to overcome these limitations. There are two types of sMSCs included in this doctoral thesis, namely solid-state dye-sensitized solar cells (sDSCs) and organometallic halide perovskite based solar cells. Two different types of HTMs, namely the small molecule organic HTM spiro-OMeTAD and the conjugated polymer HTM P3HT, were compared in sDSCs. The photo-induced absorption spectroscopy (PIA) spectra and spectroelectrochemical data suggested that the dye-dye hole conduction occurs in the absence of HTM and appears to be of significant importance to the contribution of hole transport. The PIA measurements and transient absorption spectroscopy (TAS) indicated that the oxidized dye was efficiently regenerated by a small molecule organic HTM TPAA due to its excellent pore filling. The conducting polymer P3HT was employed as a co-HTM to transfer the holes away from TPAA to prohibit the charge carrier recombination and to improve the hole transport. An alternative small molecule organic HTM, MeO-TPD, was found to outperform spiro-OMeTAD in sDSCs due to its more efficient pore filling and higher hole-mobility. Moreover, an initial light soaking treatment was observed to significantly improve the device performance due to a mechanism of Li+ ion migration towards the TiO2 surface. In order to overcome the infiltration difficulty of conducting polymer HTMs, a state-of-the-art method to perform in-situ photoelectrochemical polymerization (PEP) in an aqueous micellar solution of bis-EDOT monomer was developed as an environmental-friendly alternative pathway with scale-up potential for constructing efficient sDSCs with polymer HTMs. Three different types of HTMs, namely DEH, spiro-OMeTAD and P3HT, were used to investigate the influence of HTMs on the charge recombination in CH3NH3PbI3 perovskite based sMSCs. The photovoltage decay measurements indicate that the electron lifetime (τn) of these devices decreases by one order of magnitude in the sequence τspiro-OMeTAD > τP3HT > τDEH.