Intrinsic thermal stability of inverted perovskite solar cells based on electrochemical deposited PEDOT

Thermal stability of perovskite materials is an issue impairing the long-term operation of inverted perovskite solar cells(PSCs). Herein, the thermal attenuation mechanism of the MAPb I3films that deposited on two different hole transport layers(HTL), poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate)(PEDOT:PSS) and poly(3,4-ethylenedioxythiophene)(PEDOT), is comprehensively studied by applying a heat treatment at 85℃. The thermal stress causes the mutual ions migration of I, Pb and Ag through the device, which leads to the thermal decomposition of perovskite to form Pb I2. Interestingly, we find that I ions tend to migrate more towards electron transport layer(ETL) during heating, which is different with the observation of I ions migration towards HTL when bias pressure is applied. Moreover, the use of electrochemical deposited PEDOT as HTL significantly decreases the defect density of MAPb I3films as compared to PEDOT:PSS supported one. The electrochemical deposition PEDOT has good carrier mobility and low acidity, which avoids the drawbacks of aqueous PEDOT:PSS. Accordingly, the inverted PSCs based on PEDOT show superior durability than that with PEDOT:PSS. Our results reveal detailed degradation routes of a new kind of inverted PSCs which can contribute to the understanding of the failure of thermal-aged inverted PSCs.

Recent progress on efficient perovskite/organic tandem solar cells

The concept of tandem solar cells(TSCs) is an effective way to substantially further improve the efficiency of solar cells. The excellent optoelectronic properties and bandgap tunability of perovskites make them promising for constructing efficient TSCs. Currently, TSCs based on perovskite have been extensively studied. Besides, the performance of organic solar cells has been greatly improved recently due to the wider and more efficient spectral utilization. Accordingly, research on perovskite/organic TSCs has garnered significant attention. It has potential application advantages in emerging fields such as wearable devices by virtue of flexibility. In addition, orthogonal solvents can be adopted to realize the separate preparation of subcells with the solution method, which greatly reduces fabrication complexity;moreover, fabrication with less equipment significantly cuts down the device cost. Meanwhile, organics with more adjustability on the optoelectronic properties provide more tuning strategies for high-performance perovskite/organic TSCs. However, comprehensive and timely reviews on the perovskite/organic TSCs are deficient. Therefore, we expect to accomplish a review on this innovative TSCs to facilitate researchers with a deeper understanding of perovskite/organic TSCs. Herein, we firstly review the significant progress of perovskite and organic solar cells. Then, current achievements of perovskite/organic TSCs are summarized and introduced with a particular focus on the device structure design. Finally, we discuss existential challenges and propose effective strategies for future engineering.

Infrared response of the lateral PIN structure of a highly titanium-doped silicon-on-insulator material

The intermediate band （IB） solar cell is a promising third-generation solar cell that could possibly achieve very high efficiency above the Shockley-Queisser limit. One of the promising ways to synthesize IB material is to introduce heavily doped deep level impurities in conventional semiconductors. High-doped Ti with a concentration of 10^20 cm^-3- 10^21 cm^-3 in the p-type top Si layer of silicon-on-insulator （SOI） substrate is obtained by ion implantation and rapid thermal annealing （RTA）. Secondary ion mass spectrometry measurements confirm that the Ti concentration exceeds the theoretical Mott limit, the main requirement for the formation of an impurity intermediate band. Increased absorption is observed in the infrared （IR） region by Fourier transform infrared spectroscopy （FTIR） technology. By using a lateral p-i-n structure, an obvious infrared response in a range of 1100 nm 2000 nm is achieved in a heavily Ti-doped SOI substrate, suggesting that the improvement on IR photoresponse is a result of increased absorption in the IR. The experimental results indicate that heavily Ti-implanted Si can be used as a potential kind of intermediate-band photovoltaic material to utilize the infrared photons of the solar spectrum.

Photocurrents induced by stimulated absorption of light

In organic materials absorption of light results in creation of the Frenkel excitons, Coulomb -bound electron-hole pairs having an integer spin. Being composite bosons, Frenkel excitons may accumulate in significant quantities in a single quantum state. The probability of photon absorption by such a state increases as (N+1) where N is the occupation number of the state. This enhancement is due to the stimulated ab-sorption of light, which is a final-state stimu-lated process analogous to the well-known stimulated emission of light. We propose using the stimulated absorption for creation of solar cells of a record quantum efficiency. We are going to use the organic microspheres to ac-cumulate the Frenkel excitons at the discrete frequencies corresponding to the photonic whispering gallery modes of the sphere. The dissociation of accumulated Frenkel excitons will be effectuated periodically using the trans-parent carbon contacts on a piezoelectric mechnical support.

All-carbon nanotube diode and solar cell statistically formed from macroscopic network

Schottky diodes and solar cells are statistically created in the contact area between two macroscopic films of single-walled carbon nanotubes （SWNTs） at the junction of semiconducting and quasi-metallic bundles consisting of several high quality tubes. The n-doping of one of the films allows for photovoltaic action, owing to an increase in the built-in potential at the bundle-to-bundle interface. Statistical analysis demonstrates that the Schottky barrier device contributes significantly to the I-V characteristics, compared to the p-n diode. The upper limit of photovoltaic conversion efficiency has been estimated at N20%, demonstrating that the light energy conversion is very efficient for such a unique solar cell. While there have been multiple studies on rectifying SWNT diodes in the nanoscale environment, this is the first report of a macroscopic all-carbon nanotube diode and solar cell.

Structural, optical and electrical properties of ZnO： B thin films with different thickness for bifacial a-Si：H/c-Si heterojunction solar cells

Textured surface boron-doped zinc oxide （BZO） thin films were fabricated by metal organic chemical vapor deposition as transparent conductive oxide （TCO） for solar cells. The surface microstructure was characterized by X-ray diffraction spectrum and scan- ning electron microscope. The optical transmittance was shown by optical transmittance microscope and the electrical properties were tested by Hall measurements. The thickness of the BZO film has crucial impact on the surface morphology, optical transmittance, and resistivity. The electrical and optical properties as well as surface microstructure varied inconsistently with the increase of the film thickness. The grain size and the surface roughness increased with the increase of the film thickness. The conductivity increased from 0.96x 103 tO 6.94x 103 S/cm while the optical transmittance decreased from above 85% to nearly 80% with the increase of film thickness from 195 to 1021 nm. The BZO films deposited as both front and back transparent electrodes were applied to the bifacial p- type a-Si：H/i-type a-Si：H/n-type c-Si/i-type a-Si：H/n＋-type a-Si：H heterojunction solar cells to obtain the optimized parameter of thickness. The highest efficiency of all the samples was 17.8% obtained with the BZO film thickness of 829 nm. Meanwhile, the fill factor was 0.676, the open- circuit voltage was 0.63 Vand the short-circuit density was 41.79 mA/cm2. The properties of the solar cells changing with the thickness were also investigated.

Influence of defect density on the ZnO nanostructures of dye-sensitized solar cells

The relationship between bilayer nanostructure, defect density and dye-sensitized solar cell （DSCC） per- formances was investigated. By adjusting bilayer nano- structures, defect density of ZnO nanodendrite-nanorods structure was decreased comparing to that of nanoflower- nanorods structure. The performances of DSCC based on ZnO nanodendrites-nanorods structure and nanoflower- nanorods structure were studied by Raman spectrum, room temperature photoluminescence, dye loading, photocurrent density-voltage characteristic and open-circuit voltage decay （OCVD） technique. The device with nanodendrite- nanorods structure has lower charge recombination rate and prolonged electron lifetime due to its microstructure feature.