High-efficiency organic-inorganic hybrid perovskite solar cells have experienced rapid development and attracted significant attention in recent years. However, instability to an ambient environment such as moisture is a facile challenge for the application of perovskite solar cells. Herein, 1,8-octanediammonium iodide (ODAI) is employed to construct a two-dimensional modified interface by in situ combined with residual PbI2 on the formamidinium lead iodide (FAPbI(3)) perovskite surface. The ODA(2+ )ion seems to lie horizontally on the surface of a three-dimensional perovskite due to its substitution for two FA(+) ions, which could protect the bulk perovskite more effectively. The unencapsulated perovskite solar cells showed notably improved stability, which remained 92% of its initial efficiency after storing in an ambient environment for 120 days. In addition, a higher open-circuit voltage of 1.13 V compared to that of the control device (1.04 V) was obtained due to the interface energy level modification and defect passivation. A champion power conversion efficiency of 21.18% was therefore obtained with a stabilized power output of 20.64% at the maximum power point for planar perovskite solar cells.

The performance of perovskite solar cells (PSCs) depends on the crystallization of the perovskite layer. Herein, we demonstrate an effective photoannealing (PA) process by a halogen lamp. During the PA process, on the one hand, the lower energy photon, that is, near IR up to similar to 1015 nm photon, drives the crystallization of the perovskite film, similar to the conventional thermal annealing (TA). On the other hand, the higher energy photon of PA can excite the trapped carriers and release the space charges, thus leading to an ideal perovskite layer with better crystallinity and lower density of defect when compared to that of TA. A maximum power conversion efficiency (PCE) has been obtained to be 20.41% in the CH3 NH3 PbI3 -based planar PSCs based on PA because of the increase of J(sc) and V-oc, much higher than the control device based on the conventional TA with a maximum PCE of 18.08%. Therefore, this result demonstrates that PA is an effective method to promote the device performances and reduce the fabrication cost, which provides a potential approach for the commercial application of perovskite devices.

Perovskite solar cells (PSCs) have been paid more attention because of its high power conversion efficiency (PCE) and flexible applications. Low temperature process for PSCs is critical for high performance flexible devices and industrial applications. Herein, the photovoltaic properties of the PSCs based on a polyelectrolyte interfacial layer of polyethyleneimine (PEI) were studied in this work and the configuration of PSCs was indium fin oxide (ITO)/PEI/SnO2/perovskite/spiro-OMeTAD/Ag. Due to the spin-coated PEI on ITO substrates, smooth cathodes (ITO/PEI) with low work function were obtained and the champion PCE of 19.36% and 16.81% for the rigid and flexible devices respectively was achieved accordingly. Moreover, the PCE of the rigid and flexible PSCs with PEI (0.1 mg mL(-1)) remained similar to 95% and similar to 90% of the initial values respectively after 80 days in ambient conditions. Meanwhile, the PCE of the flexible PSCs based on PEI (0.1 mg mL(-1)) remained 85% of the initial value after 100 bending cycles and the bendability of the flexible PSCs was improved accordingly. All the experimental data implied that the fabrication of PEI onto ITO electrodes was an effective way to promote the photovoltaic properties of the low-temperature processed rigid and flexible PSCs.

Organic-inorganic metal halide perovskites have drawn a great deal of attention due to their supreme optical and electrical properties and their potential in future application in optoelectronic devices. Here, we carry out finite-difference time-domain (FDTD) simulation on different experimentally realistic structures of perovskite solar cells (PSC) and optimize their parameters with assistance of neural network (NN). We find an optimized structure with 30.48% enhancement comparing to planar structure and the fact that with properly design, 300-nm-thick nano-textured structure can outperform 900-nm-thick planar structure. We believe that light trapping structure is essential in thin film PSCs and also has a great potential in lead-free PSCs.

Compared with silicon-based solar cells, organic-inorganic hybrid perovskite solar cells (PSCs) possess a distinct advantage, i.e., its application in the flexible field. However, the efficiency of the flexible device is still lower than that of the rigid one. First, it is found that the dense formamidinium (FA)-based perovskite film can be obtained with the help of N-methyl-2-pyrrolidone (NMP) via low pressure-assisted method. In addition, CH3NH3Cl (MACl) as the additive can preferentially form MAPbCl(3-)(x)I(x) perovskite seeds to induce perovskite phase transition and crystal growth. Finally, by using FAI center dot PbI2 center dot NMP+x%MACl as the precursor, i.e., ligand and additive synergetic process, a FA-based perovskite film with a large grain size, high crystallinity, and low trap density is obtained on a flexible substrate under ambient conditions due to the synergetic effect, e.g., MACl can enhance the crystallization of the intermediate phase of FAI center dot PbI2 center dot NMP. As a result, a record efficiency of 19.38% in flexible planar PSCs is achieved, and it can retain about 89% of its initial power conversion efficiency (PCE) after 230 days without encapsulation under ambient conditions. The PCE retains 92% of the initial value after 500 bending cycles with a bending radii of 10 mm. The results show a robust way to fabricate highly efficient flexible PSCs.

Due to the difficulty in achieving high efficiency and high color purity simultaneously, blue emission is the limiting factor for the performance and stability of OLEDs. Since 2003, we have been working on organic light-emitting diodes (OLEDs), especially on blue light. After a series of molecular designs, novel strategies have been proposed from different aspects. At first, highly efficient deep blue emission could be achieved through molecular design with highly twisted structure to suppress fluorescence quenching and redshift. Deep blue emitters with high efficiency in solid state, a twisted structure with aggregation induced emission (AIE) characteristics was incorporated to inhibit molecular aggregation, and triplet-triplet fusion (TTF) and hybridized localized charge transfer (HLCT) were adopted to increase the ratio of triplet exciton used. Secondly, a highly efficient blue OLED could be achieved through improving charge transport. New electron transport materials (ETMs) with wide band gap were developed to control charge transport balance in devices. Thirdly, a highly efficient deep blue emission could be achieved through a mesoscopic structure of out-coupling layer. A mesoscopic photonic structured organic thin film was fabricated on the top of metal electrode by self-aggregation in order to improve the light out-coupling efficiency.

Interface modification engineering has been widely used as a flexible and effective method to optimize the performance of perovskite photovoltaic devices. Herein, we adopt NiCl2 as a modifier to passivate the interface at the electron transporting layer (ETL) and perovskite layer to drive high-efficiency perovskite solar cells (PSCs) with increased open circuit voltage (V-oc) and neglectable hysteresis. The devices based on SnO2/NiCl2 ETL achieved a high V-oc (1.17 V) and power conversion efficiency (PCE) (19.46%). The improvement is attributed to the increased energy level of the conduction band minimum (E-CBM) and reduced defect states by NiCl2 interface modification. Our findings provide an effective way to obtain higher V-oc and PCE values as well as neglectable hysteresis for planar PSCs.

Compared with silicon-based solar cells, organic-inorganic hybrid perovskite solar cells (PSCs) possess a distinct advantage, i.e., its application in the flexible field. However, the efficiency of the flexible device is still lower than that of the rigid one. First, it is found that the dense formamidinium (FA)-based perovskite film can be obtained with the help of N-methyl-2-pyrrolidone (NMP) via low pressure-assisted method. In addition, CH3NH3Cl (MACl) as the additive can preferentially form MAPbCl(3-)(x)I(x) perovskite seeds to induce perovskite phase transition and crystal growth. Finally, by using FAI center dot PbI2 center dot NMP+x%MACl as the precursor, i.e., ligand and additive synergetic process, a FA-based perovskite film with a large grain size, high crystallinity, and low trap density is obtained on a flexible substrate under ambient conditions due to the synergetic effect, e.g., MACl can enhance the crystallization of the intermediate phase of FAI center dot PbI2 center dot NMP. As a result, a record efficiency of 19.38% in flexible planar PSCs is achieved, and it can retain about 89% of its initial power conversion efficiency (PCE) after 230 days without encapsulation under ambient conditions. The PCE retains 92% of the initial value after 500 bending cycles with a bending radii of 10 mm. The results show a robust way to fabricate highly efficient flexible PSCs.

Due to the difficulty in achieving high efficiency and high color purity simultaneously, blue emission is the limiting factor for the performance and stability of OLEDs. Since 2003, we have been working on organic light-emitting diodes (OLEDs), especially on blue light. After a series of molecular designs, novel strategies have been proposed from different aspects. At first, highly efficient deep blue emission could be achieved through molecular design with highly twisted structure to suppress fluorescence quenching and redshift. Deep blue emitters with high efficiency in solid state, a twisted structure with aggregation induced emission (AIE) characteristics was incorporated to inhibit molecular aggregation, and triplet-triplet fusion (TTF) and hybridized localized charge transfer (HLCT) were adopted to increase the ratio of triplet exciton used. Secondly, a highly efficient blue OLED could be achieved through improving charge transport. New electron transport materials (ETMs) with wide band gap were developed to control charge transport balance in devices. Thirdly, a highly efficient deep blue emission could be achieved through a mesoscopic structure of out-coupling layer. A mesoscopic photonic structured organic thin film was fabricated on the top of metal electrode by self-aggregation in order to improve the light out-coupling efficiency.

Interface modification engineering has been widely used as a flexible and effective method to optimize the performance of perovskite photovoltaic devices. Herein, we adopt NiCl2 as a modifier to passivate the interface at the electron transporting layer (ETL) and perovskite layer to drive high-efficiency perovskite solar cells (PSCs) with increased open circuit voltage (V-oc) and neglectable hysteresis. The devices based on SnO2/NiCl2 ETL achieved a high V-oc (1.17 V) and power conversion efficiency (PCE) (19.46%). The improvement is attributed to the increased energy level of the conduction band minimum (E-CBM) and reduced defect states by NiCl2 interface modification. Our findings provide an effective way to obtain higher V-oc and PCE values as well as neglectable hysteresis for planar PSCs.

Organic inorganic perovskite solar cells have seen tremendous developments in recent years. As a hole transport material, 2,2',7,7'-tetrakis(N,N-di-p-methoxyphenylamine)-9,9'-spirobifluorene (Spiro-OMe-TAD) is widely used in n-i-p perovskite solar cells. However, it may lead to the perovskite film degradation due to the dopant lithium bis-((trifluoromethyl)sulfonyl)amide (Li-TFSI), which has strong hydrophilicity. Cu9S5 is considered as a superior p-type transport material, which also has a favorable energy level matching with the highest occupied molecular orbital of Spiro-OMeTAD. Herein, a solution-processed organic-inorganic-integrated hole transport layer was reported, which is composed of the undoped Spiro-OMeTAD and Cu9S5 layer. Since there is no Li-TFSI doping, it is extremely conductive to the long-term stability of the solar cells. In the meantime, we proposed a method to adjust the lowest unoccupied molecular orbital (LUMO) of SnO2 via nitrogen implantation (N:SnO2). The LUMO of SnO2 can be tuned from -4.33 to -3.91 eV, which matches well with the LUMO of CH3NH3PbI3 (-3.90 eV), and thus helps to reduce hysteresis. The modified hole and electron transport layers were applied in n-i-p perovskite solar cells, which achieve a maximum power conversion efficiency (PCE) of 17.10 and 96% retention of PCE after 1200 h in air atmosphere without any encapsulation.