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Environment-friendly flexible Cu2ZnSn(S,Se)4 (CZTSSe) solar cells show great potentials for indoor photovoltaic market. Indoor lighting is weak and multi-directional, thus the researches of photovoltaic device structures, techniques and performances face new challenges. Here, we design symmetrical bifacial CZTSSe solar cells on flexible Mo-foil substrate to efficiently harvest the indoor energy. Such devices are fabricated by double-sided deposition techniques to ensure bifacial consistency and save cost. We report 9.3% and 9% efficiencies for the front and back sides of the flexible CZTSSe solar cell under the standard sun light. Considering the indoor environment, we verify weak-light response performance of the devices under LED illumination and flexibility properties after thousands of bending. Bifacial CZTSSe solar cells in parallel achieve the superposition of double-sided output current from multi-directional light, significantly enhancing the area utilization rate. The present results and methods are expected to expand indoor photovoltaic applications. Indoor lighting is weak and multi-directional, thus the requirement for photovoltaic differs from that designed for outdoor. To efficiently harvest the indoor energy, the authors designed CZTSSe bifacial solar cells on flexible Mo substrate using double-sided deposition to ensure consistency and to save cost. [ABSTRACT FROM AUTHOR]

We present a self-cleaning organic solar cells (OSCs) with a light-trapping structure by introducing a groove-shaped micro/nanostructured haze thin films (GHFs). The GHF with periods larger than wavelengths of incident light can broaden the effective optical paths and promote the diffused lights, while keeping high (low) total transmission (reflectance) properties. When laminated GHF on top of the light-in side of OSCs, the power conversion efficiency of OSCs is improved more than 10%. Simultaneously, the superhydrophobic GHF composed of the groove structure allows the droplets to successfully remove dust particles from the polydimethylsiloxane (PDMS) surface during the roll-off process of the drop. Under 10 cycles of dust contamination and cleaning treatment, OSCs with GHF can still guarantee an initial efficiency of 84% (76%), showing great potentials of OSCs in practical applications. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The Cu 2 ZnSnS 4 (CZTS) films are prepared by sol-gel method following sulfurization. • The defects at the interface of CZTS thin film and Mo foil make the electrical properties of solar cell worse. • The Mo layer inserted between CZTS thin film and Mo foil has the effects on the properties of solar cell. • •The flexible CZTS TFSC with Mo layer inserted has a conversion efficiency of 1.58%. Abstract CZTS thin films are fabricated using sol-gel method following sulfurization. The material properties of the CZTS films which are prepared under different preheating temperatures and times are systematically investigated. The TGA-DTA analysis shows that the sulfides begin to be oxidized and the CZTS nanoparticles would be formed when the preheating temperature is above 300 °C. Moreover, with increasing the preheating temperature and time, the crystallinity of the CZTS thin films becomes stronger firstly and then weaker. Morphological characterizations show that the CZTS thin films deliver the best crystallinity under the preheating temperature of 250 °C for 5 min. The E g , resistivity, carrier concentration, and mobility of the CZTS thin films is 1.45 eV, 3.56 Ω·cm, 2.47 × 1017 cm−3, 7.12 cm2·V−1·s−1, respectively. The solar cells with the efficiency of 1.51% is successfully configured. [ABSTRACT FROM AUTHOR]

The multifunctional silica-coated Au nanobowtie (GNB@SiO2) core-shell structure was embedded in organic solar cells (OSCs), and an intense performance promotion of the devices was achieved by optimizing the shape and the size of the GNB@SiO2. The light absorption of the active layer was increased with GNB@SiO2 doping concentration increasing until the doping concentration exceeds 10 nM. The devices obtain the best J-V characteristics when GNB@SiO2 doping concentration is 10 nM. Comparing with that of the control cells, the optimal performance of the devices with GNB@SiO2 incorporated was significantly increased by 47%. The finite-difference time-domain method was used to simulate the special asymmetry shape and the size of the multifunctional GNB@SiO2 impact on the performance of the OSCs. The electric field intensity |E|2 in the different planes revealed that the local surface plasmon resonance (LSPR) and far-field scattering effect played an important role in the light absorption of the devices. The cooperation effect of LSPR near-field and the far-field scattering resulted in the electric field redistribution of the active layer as the result of the absorption enhanced. [ABSTRACT FROM AUTHOR]

Cation substitution has an important impact on the power conversion efficiency (PCE) of Cu 2 ZnSn(S,Se) 4 (CZTSSe) solar cells. Herein, a significant PCE enhancement of flexible indium-doped CZTSSe solar cells has been achieved by partially substituting Sn4+ with In3+. Systematic measurements indicate that In doping in CZTSSe film effectively improves the crystallinity and carrier concentration of the absorber layer. Meanwhile, the treatment reduces interface recombination and band tailing by passivating deep defects and increases the open-circuit voltage (V oc) of the solar cells. By physical analysis, the key parameters for the solar cell diode such as A , J 0 , R s and R sh are significantly improved after In-doping, indicating better PN junction quality. Under the optimal In-doping (x = In/(Sn + In) = 9%), the flexible Cu 2 ZnSn 1- x In x (S,Se) 4 solar cell has been successfully obtained with the best efficiency of 7.19% and the V oc enhancement of 62 mV due to reduced V oc deficit and band tailing. • Flexible CZTISSe solar cells with efficiency of 7.19% are obtained via In doping. • Doping In can improve the V oc and carrier transportation of the solar cells. • Effects of In doping on CZTISSe films and solar cells have been systematically studied. [ABSTRACT FROM AUTHOR]

Partial cation substitution is an effective way to inhibit defects and carrier recombination, which can improve the efficiency of Cu2ZnSn(S,Se)4 (CZTSSe) solar cells. Herein, flexible Cu2Zn1−xCdxSn(S,Se)4 (x = 0–15%) solar cells are fabricated on Mo foils with partial Cd substitution for Zn via a green solution‐process. The best device performance can be achieved when Cd/(Zn + Cd) = 8%, with an efficiency up to 6.49% and a significantly improved device repeatability. The EU decreases from 24 to 15 meV, indicating that antisite defects and band tailings are effectively suppressed. C–V data reveal that Wd and Vbi are enhanced after doping Cd, resulting in a stronger built‐in electric field which facilitates Fermi‐level splitting and hence increases band bending of the absorber toward the junction interface. Furthermore, the mechanism of current shunting is studied using an equivalent circuit model with three parallel current pathways to fit J–V curves. The key parameters for the solar cell diode such as A, J0, and Rsh are significantly improved by partially substituting Zn with Cd, demonstrating that current shunting loss is suppressed and the junction quality is improved, resulting in a significant improvement in device repeatability. [ABSTRACT FROM AUTHOR]

• A pyramid-shaped micron-structured PDMS film was used in organic solar cells. • The size of the pyramid plays an important role of the devices performance. • The power conversion efficiency of PTB7-Th: PC 71 BM-based cells reaches to 10.18%. • The devices with the pyramid-shaped PDMS film presents better stability. Since the light harvesting of the organic solar cells (OSCs) is limited by the ultra-thin active layer film due to the low carrier mobility of the organic materials. This study presents a tractable and cost-effective method for enhancement of the light capture of OSCs. A pyramid-shaped micron-structured polydimethylsiloxane (MST-PDMS) anti-reflection film was pasted on the back surface of the OSCs. The MST-PDMS film can reduce the reflectivity of incident light and enhance light capture. Comparing with that of the devices based on the normal indium tin oxide (ITO) glass substrates, the performance of the devices with MST-PDMS was significant improved. The size of the pyramid is an important factor to the performances of the devices. The short circuit current density could increase mostly without sacrificing the open circuit voltage and fill factor, when the width of the pyramid is 9 µm, and a maximum power conversion efficiency (PCE) of PTB7-Th: PC 71 BM-based OSCs reaches to 10.18%. Compared with that of the device without the anti-reflection film, PCE was increased by 17.96%. Further, the OSCs with the pyramid-shaped MST-PDMS exhibits a relatively high hydrophobic properties leading to a better stability of the devices at the ambient environment. [ABSTRACT FROM AUTHOR]

• Ti doping Sb 2 S 3 films without oxide/hydroxide were prepared by the spin-casting. • Solar cells structure of FTO/TiO 2 /Ti:Sb 2 S 3 /P3HT/Al is fabricated. • The performance of Sb 2 S 3 based solar cells is great improved by Ti doping. The inorganic-organic hybrid solar cells based on Ti doped antimony sulfide (Ti:Sb 2 S 3) was prepared by a simple spin-casting method. Compared with that of the devices with the pristine Sb 2 S 3 , the power conversion efficiency (PCE) of the devices based on Ti:Sb 2 S 3 was increased by 41%. The different Ti doping concentration impact on the performance of the devices was investigated. PCE of the cells was improved with Ti doping concentration increased until Ti concentration exceeds 6%, the highest PCE reaches to 2.70%. The better performance of the devices based on Ti:Sb 2 S 3 is due to the improved optical absorption, and the decreased dangling bonds on the surface of the Ti:Sb 2 S 3 thin film. [ABSTRACT FROM AUTHOR]