CIGS thin films were irradiated with 100 or 250 keV electrons to reveal the radiation defect by analyzing PL measurement. The PL intensity decreased due to non-radiative recombination defects induced by electron irradiation. Furthermore, the intensity 0.8 eV peak of the PL spectrum was observed from CIGS films irradiated with 250 eV electrons and is said to correspond to In-antisite defects in CIGS materials. The defects can usually change into InCu-VCu complex defects combined with VCu, since the formation energy of the complex defect is lower than that of each defect. Cu interstitial defects induced by 250 keV electron irradiation would diffuse to VCu of the complex defect, whereupon the complex defect might become an In-antisite defect due to 250 keV electron irradiation.

Two alternative chemical etchings (aqueous solution of bromine and bromine methanol solution) have been here tested to replace the KCN etching step in Cu-rich CuInSe2 based solar cells fabrication process. This new oxidative etch aims also at smoothing and thinning the as-grown films. This directly affects the interface between the absorber and the CdS buffer, interface which causes problems for Cu-rich solar cells. We present here the effect of these two alternative etchings on both the absorber surface and the solar cells parameters: whereas the bromine methanol etching destroys the solar cell, the aqueous solution of bromine leads to an improvement of the device through reduced interface and tunneling enhanced recombination.

Perovskite solar cells have caught wide attention. High efficiency, low-cost and high stability are among the major goals, which could eventually move the perovskite solar cells to the market. To achieve these goals, interface deliberation and nanostructural engineering hold the key.

We have investigated the film morphology and photoluminescence properties of spin-coated CH3NH3PbI3-xClx films on mesoporous and compact TiO2 substrates. We observe that the perovskite film deposited on the mesoporous substrate composed of 20 nm TiO2 nanopaticles exhibits relatively uniform grain size, while the films deposited on the compact TiO2 substrate and the mesoporous substrate with large TiO2 nanoparticles (200 nm) show highly heterogeneous film morphology. The heterogeneity of film morphology has significant effect on the photoluminescence spectra and lifetime of the perovskite films. The result of time-resolved confocal microscopy unveils the relation between film structure and photoluminescence properties.

Performance of a perovskite based solar cell is highly determined by the crystalline qualities of the perovskite thin film sandwiched between an electron and a hole transport layer, such as grain size and uniformity of the film. Here, we demonstrated a new hybrid physical-chemical vapor deposition (HPCVD) technique to synthesis high quality perovskite films. First, a PbI2 precursor film was spin-coated on a mesoporous TiO2 (m-TiO2)/compact TiO2 (c-TiO2)/FTO substrate in ambient environment. Then, purified CH3NH3I crystal material was evaporated and the vapor reacted with the PbI2 precursor film in a vacuum pressure/temperature accurately controlled quartz tube furnace. In this technique, high vacuum (2mTorr) and low temperature (100°C) were applied to decrease perovskite film growth rate and reduce perovskite film defects. After vapor reaction, the perovskite film was annealed at 100°C for 10min in 20mTorr vacuum to recrystallize and remove CH3NH3I residue in order to further improve crystal quality of the thin film. Crystal quality of this perovskite thin film was characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), and X-ray diffraction (XRD). SEM and AFM results illustrate perovskite thin films synthesized by this technique have larger grain sizes and more uniformity (RMS 11.6nm/Ra 9.3nm) superior to most existing methods. Strong peaks shown in the XRD chart at 14.18°, 28.52°, 31.96°, which were assigned to (110), (220), (330) miller indices of CH3NH3PbI3 perovskite crystal, indicate the complete reaction between CH3NH3I vapor and PbI2 precursor layer. High power conversion efficiency (PCE) up to 12.3% and stable efficiencies under four hours illumination of AM1.5 standard were achieved by these solar cells. This vacuum/vapor based technique is compatible with conventional semiconductor fabrication techniques and high quality perovskite film could be achieved through delicate process control. Eventually, perovskite based solar cells could be mass produced in low cost for large scale applications by this novel technique.

Long term stability of mixed perovskite compounds is one of the important concerns for prolonged viability and economical use of perovskite based solar cells. Degradation in perovskite films mainly occurs due to exposure to moisture. Hence, a controlled atmospheric condition and lower humidity is preferred for device fabrication and use. Many different strategies such as use of thin and wide band gap semiconductor layer, improvement in pour filling of metal oxide film, and utilization of AgTFSI have been attempted to improve device stability. However, for long term durability, there is an urgent need to increase stability of parent perovskite layer, apart from use of protective layers. In this study we examined water resistant additive, structural modifications, and stoichiometric modification for enhanced film durability. These strategies and preliminary results are discussed in this report.

Hybrid organic/silicon heterostructures have become of great interest for photovoltaic application due to their promising features (e.g. easy fabrication in a low-temperature process) for cost-effective photovoltaics. This work is focused on solar cells with a hybrid heterojunction between the polymer poly(3-hexylthiophene-2,5-diyl) (P3HT) and n-doped monocrystalline silicon. As semi-transparent top contact, a thin (15 nm) Au layer was employed. Devices with different P3HT thicknesses were processed by spin-casting and compared with a reference Au/n-Si Schottky diode solar cell.

The current density-voltage (J-V) measurements of the hybrid devices show a significant increase in open-circuit voltage (VOC) from 0.29 V up to 0.50 V for the best performing hybrid devices compared to the Schottky diode reference, while the short-circuit current density (JSC) does not change significantly. The increased VOC indicates that P3HT effectively reduces the reverse electron current into the gold contact. The wavelength-dependent JSC measurements show a decreased JSC in the wavelength range of P3HT absorption. This is related to the reduced JSC generation in silicon not being compensated by JSC generation in P3HT. It is concluded that the charge generation in P3HT is less efficient than in silicon.

After a thermal annealing of the hybrid P3HT/silicon solar cells, we achieved power conversion efficiencies (PCE) (AM1.5 illumination) up to 6.5% with VOC of 0.52 V, JSC of 18.6 mA/cm² and a fill factor (FF) of 67%. This is more than twice the efficiency of the reference Schottky diode.

A non-aqueous Poly(3,4-ethylenedioxythiophene): poly(styrenesulfonic acid) (PEDOT:PSS) dispersion was developed to enable the accommodation of non-polar additives. This additional functionalisation targets selected interface characteristics and results in an improved adhesion of PEDOT:PSS on the photo-active layer. Such mechanical robustness is paramount in inverted organic photovoltaic cells contributing to improved long-term stability.

The goal of this research is to synthesize novel linear and hyperbranched polythiophene derivatives containing diketopyrrolopyrrole (DPP) as linking groups, and to investigate thermal, optical, electrochemical, and photovoltaic properties of those derivatives. Polymers with high regioregularity were synthesized via the Universal Grignard metathesis polymerization. Those linear or hyperbranched polythiophenes containing DPP bridging moieties showed higher molecular weights and better thermal stability compared with normal P3HT. The UV-vis absorption spectra of the DPP-containing polymers are similar to that of P3HT in film state, while they show distinct attenuation in fluorescent emission. Finally, all polymers were blended with PC61BM and used as active layers for fabrication of inverted solar devices. The devices based on those DPP-containing polythiophenes revealed the open-circuit voltage (VOC) of 0.55–0.58 V, the short-circuit current (JSC) of 8.62–16.21 mA/cm2, the fill factor (FF) of 36–41%, and the power conversion efficiency (PCE) of 1.73–3.74%.