Suppression Of Interfacial Recombination Research Articles

Effect of Cu‐deficient layer formation in Cu(In,Ga)Se2 solar‐cell performance

AbstractCu‐deficient layer (CDL) on Cu(In,Ga)Se2 (CIGS) promotes Cd diffusion from CdS buffer layer and forms a valence band offset (ΔEV) between CDL and CIGS. We quantitively demonstrate the effects of CDL formation on the performance of CIGS solar cells through experiments and theoretical simulation. To investigate the effects of Cd diffusion and ΔEV by CDL, theoretical analysis was carried out for a CIGS solar cell with a surface layer which simulated the CDL at CdS/CIGS interface. It was revealed that when electron concentration in n‐type surface layer is higher than the absolute carrier concentration in CIGS absorber (ND > |NA, CIGS|), open‐circuit voltage and fill factor are improved. Additionally, ΔEV ≥ 0.15 eV leads to the highest open‐circuit voltage by suppression of interfacial recombination. Transmission electron microscope energy dispersive X‐ray spectrometry and scanning spreading resistance microscopy were employed for the same cross section of a CIGS solar cell fabricated by three‐stage process. Despite CDL with Cu/(Ga + In) of 0.31 formed on the surface had high Cd contents of 3.4 at%, its carrier concentration of 4.8 × 1010 cm−3 was lower than that of 1014 –1016 cm−3 in grain interior owing to insufficient activation of Cd atoms. These results indicate the effectiveness of ΔEV formation by introducing CDL with low Cu/(Ga + In) of 0.31 to boost CIGS solar cell performance and difficulty in realizing ND > |NA, CIGS| by surface Cd doping.

Enhancement of the efficiency and stability of planar p-i-n perovskite solar cells via incorporation of an amine-modified fullerene derivative as a cathode buffer layer

A methanol-soluble diamine-modified fullerene derivative (denoted as PCBDANI) was applied as an efficient cathode buffer layer (CBL) in planar p-i-n perovskite solar cells (pero-SCs) based on the CH3NH3PbI3–x Cl x absorber. The device with PCBDANI single CBL exhibited significantly improved performance with a power conversion efficiency (PCE) of 15.45%, which is approximately 17% higher than that of the control device without the CBL. The dramatic improvement in PCE can be attributed to the formation of an interfacial dipole at the PCBM/Al interface originating from the amine functional group and the suppression of interfacial recombination by the PCBDANI interlayer. To further improve the PCE of pero-SCs, PCBDANI/LiF double CBLs were introduced between PCBM and the top Al electrode. An impressive PCE of 15.71% was achieved, which is somewhat higher than that of the devices with LiF or PCBDANI single CBL. Besides the PCE, the long-term stability of the device with PCBDANI/LiF double CBLs is also superior to that of the device with LiF single CBL.

Oriented rutile TiO2 nanorod arrays for efficient quantum dot-sensitized solar cells with extremely high open-circuit voltage

TiO2 nanoparticles are typically employed to construct the porous films for quantum dot-sensitized solar cells (QDSCs). However, undesirable interface charge recombination at grain boundaries would hinder the efficient electron transport to the conducting substrate, giving rise to the decline of open-circuit voltage (Voc). In this work, vertically aligned architectures of oriented one-dimensional (1D) TiO2 nanorod arrays hydrothermally grown on substrates pave a way in designing highly efficient QDSCs with efficient radial-directional charge transport. SEM, TEM, XRD, and Raman spectroscopy were employed to characterize the as-prepared TiO2 nanorods, showing the rutile phase with single-crystalline structure. The homogeneous deposition of CdS/CdSe QDs on the surface of TiO2 nanorods has been achieved by in-situ grown strategies (i.e., successive ionic layer absorption and reaction, and chemical bath deposition). An extremely high Voc value up to 0.77V has been achieved for CdS/CdSe QDSCs based on the well-ordered 1D nanorod arrays. To the best of our knowledge, it is the highest Voc reported for TiO2-based QDSCs. Dependencies of photovoltaic performance, optical absorption, and interfacial charge behavior on the length of nanorods were systematically investigated. A 1.7μm nanorod-array photoelectrode-based QDSC delivers a remarkable power conversion efficiency up to 3.57% under simulated AM 1.5 100mWcm−2 illumination, attributed to the balance of competition between the increase of QD loading and suppression of interfacial recombination. This work highlights the combination of QDs with high absorption coefficient 1D architectures possessing efficient charge transport for constructing high efficiency solar cells.