Organometal halide perovskite is a promising material in photovoltaic (PV) cells. Within a short time, its performance has increased dramatically to become a real competitor to silicon solar cells. Here we report on the temperature dependence (annealing temperature and the dependence of the photovoltaic parameters on temperature) of formamidinium (FA) lead iodide (FAPbI3), methylammonium (MA) lead iodide (MAPbI3) and their mixture (MAPbI3 : FAPbI3) in hole conductor free perovskite solar cells. These three types of perovskites function both as light harvesters and as hole conductors. Surface photovoltage and optical characterization reveal the p-type behavior and the band gap of the different perovskites. We observed that the ratio between the MA and FA cations might change during the annealing process, affecting the band gap and the stability of the layers. The PV parameters at different temperatures show better stability for the pure MAPbI3 and FAPbI3 solar cells compared to their mixture. Using intensity modulated photovoltage/photocurrent spectroscopy, we found that the diffusion length is weakly dependent on the light intensity, while the charge collection efficiency drops with light intensity for the FAPbI3-based cells. However, for MAPbI3 and the mixture, the charge collection efficiency remains constant for a wide range of light intensities.
Organo metal halide perovskite has attracted considerable attention recently due to its distinctive properties that make it especially useful in photovoltaic solar cells. In this work we demonstrate high open circuit voltage of 1.35 V using Al2O3/CH3NH3PbBr3 perovskite solar cells without a hole conductor. The contact potential difference under light measured by surface photovoltage spectroscopy of CH3NH3PbBr3 was more than twice that of CH3NH3PbI3, which results in smaller surface potential for the Al2O3/CH3NH3PbBr3 cells. Incident modulated photovoltage spectroscopy shows a longer recombination lifetime for the Al2O3/CH3NH3PbBr3 cells than for the TiO2/CH3NH3PbI3 cells or for the TiO2/CH3NH3PbBr3 cells, further supporting the high open circuit voltage. The possibility to gain high open circuit voltage even without a hole transport material in perovskite solar cells shows that the perovskite/metal oxide interface has a major effect on the open circuit voltage in perovskite based solar cells.
We report for the first time on co-sensitization between CH3NH3PbI3 perovskite and PbS quantum dots (QDs) in a heterojunction solar cell to obtain a panchromatic response from the visible to near IR regions. Following the deposition of the sensitizers on a TiO2 film, an Au thin layer is evaporated on top as a back contact. Importantly, the CH3NH3PbI3 nanoparticles and the PbS QDs used here simultaneously play both the role of a light harvester and a hole conductor, rendering superfluous the use of an additional hole transporting material. The mesoscopic CH3NH3PbI3 (perovskite)–PbS (QD)/TiO2 heterojunction solar cell shows an impressive short circuit photocurrent (Jsc) of 24.63mA cm2, much higher than those of the individual CH3NH3PbI3 perovskite and the PbS QD solar cells. The advent of such co-sensitization mesoscopic heterojunction solar cells paves the way to extend the absorbance region of the promising low cost, high-efficiency perovskite based solar cells.
Organo-metal halide perovskites are composed of an ABX3 structure in which A represents a cation, B a divalent metal cation and X a halide. The organo-metal perovskite shows very good potential to be used as a light harvester in solar cells due to its direct band gap, large absorption coefficient, high carrier mobility and good stability. However, there is an important question in the photovoltaic field regarding the most advantageous architecture for perovskite based solar cells. Several studies showed sensitized perovskite solar cells achieving high performance, while high efficiency was also observed with the planar architecture. Consequently, it is still an open question regarding which operation mechanism and which architecture offers better results. This review describes both architectures, based on studies in the field. In the case of the sensitized structure, there are more difficulties in pore filling, naturally more recombination, and the possibility to use thicker metal oxide films. In the planar structure, thin metal oxide films are used, less recombination was observed and there are no infiltration problems. Both architectures exhibit long-range diffusion length and meet the demand for excellent coverage of the perovskite film.
In this work we used CH3NH3PbInBr3−n (where 0 ≤ n ≤ 3) as hole conductor and light harvester in the solar cell. Various concentrations of methylammonium iodide and methylammonium bromide were studied which reveal that any composition of the hybrid CH3NH3PbInBr3−n can conduct holes. The hybrid perovskite was deposited in two steps, separating it to two precursors to allow better control of the perovskite composition and efficient tuning of its band gap. The X-ray diffraction reveals the change in the lattice parameter due to the introducing of the Br− ions. The hybrid iodide/bromide perovskite hole conductor free solar cells show very good stability, their power conversion efficiency achieved 8.54% under 1 sun illumination with current density of 16.2 mA/cm2. The results of this work open the possibility for graded structure of perovskite solar cells without the need for hole conductor.
The inorganic–organic perovskite is currently attracting a lot of attention due to its use as a light harvester in solar cells. The large absorption coefficients, high carrier mobility and good stability of organo-lead halide perovskites present good potential for their use as light harvesters in mesoscopic heterojunction solar cells. This work concentrated on a unique property of the lead halide perovskite, its function simultaneously as a light harvester and a hole conductor in the solar cell. A two-step deposition technique was used to optimize the perovskite deposition and to enhance the solar cell efficiency. It was revealed that the photovoltaic performance of the hole conductor free perovskite solar cell is strongly dependent on the depletion layer width which was created at the TiO2–CH3NH3PbI3 junction. X-ray diffraction measurements indicate that there were no changes in the crystallographic structure of the CH3NH3PbI3 perovskite over time, which supports the high stability of these hole conductor free perovskite solar cells. Furthermore, the power conversion efficiency of the best cells reached 10.85% with a fill factor of 68%, a Voc of 0.84 V, and a Jsc of 19 mA cm2, the highest efficiency to date of a hole conductor free perovskite solar cell.
Lead halide perovskite is an excellent candidate for use as a light harvester in solar cells. Our work presents a depleted hole conductor free CH3NH3PbI3/TiO2 heterojunction solar cell using a thick CH3NH3PbI3 film. The CH3NH3PbI3 formed large crystals which function simultaneously as light harvesters and as hole transportmaterials. We performed capacitance voltage measurements, which show a depletion regionwhich extends to both n and p sides. The built-in field of the depletion region assists in the charge separation and suppresses the back reaction of electrons from the TiO2 film to the CH3NH3PbI3 film. This depleted hole conductor free CH3NH3PbI3/TiO2 heterojunction solar cell provides a power conversion efficiency of 8% with a current density of 18.8 mA cm2, the highest efficiency achieved to date for perovskite based solar cells without a hole conductor.
We prepared a quasi-solid electrolyte for dye-sensitized solar cells (DSSCs) that consist of ionic liquid and modified silica particles. Commercial bare silica F5 particles and modified silica F5 by NH2 and NH3+ groups were prepared, and fully characterized. The best photovoltaic performance was observed using the NH2 modified silica particles giving an open circuit voltage (Voc) of 815 mV, a short-circuit current (Jsc) of 11.23 mA cm-2, and a fill factor (FF) of 0.75 corresponding to an overall power conversion efficiency of 7.04% at 100 mW cm-2 AM 1.5. The modification of the silica particles by NH2 groups increases the Voc of DSSCs by around 60 mV compared to pure ionic liquid electrolyte based DSSCs.
Photovoltaic cells use semiconductors to convert sunlight into electrical current and are regarded as a key technology for a sustainable energy supply. Quantum dot-based solar cells have shown great potential as next generation, high performance, low-cost photovoltaics due to the outstanding optoelectronic properties of quantum dots and their multiple exciton generation (MEG) capability. This review focuses on QDs as light harvesters in solar cells, including different structures of QD-based solar cells, such as QD heterojunction solar cells, QD-Schottky solar cells, QD-sensitized solar cells and the recent development in organic-inorganic perovskite heterojunction solar cells. Mechanisms, procedures, advantages, disadvantages and the latest results obtained in the field are described. To summarize, a future perspective is offered.