24.04.15 KB. OK to add published OA paper to spira

Perovskites with bandgaps between 1.7 and 1.8 eV are optimal for tandem configurations with crystalline silicon (c-Si) because they facilitate efficient harvest of solar energy. In that respect, achieving a high open-circuit voltage (V OC ) in such wide-bandgap perovskite solar cells is crucial for a high overall power conversion efficiency (PCE). Here, we provide key insights into the factors affecting the V OC in wide-bandgap perovskite solar cells. We show that the influence of the hole transport layer (HTL) on V OC is not simply through its ionization potential but mainly through the quality of the perovskite−HTL interface. With effective interface passivation, we demonstrate perovskite solar cells with a bandgap of 1.72 eV that exhibit a V OC of 1.22 V. Furthermore, by combining the high-V OC perovskite solar cell with a c-Si solar cell, we demonstrate a perovskite−Si four-terminal tandem solar cell with a PCE of 27.1%, exceeding the record PCE of single-junction Si solar cells.

Here we report the investigation of controlled PbI2 secondary phase formation in CH3NH3PbI3 (MAPI) photovoltaics through post-deposition thermal annealing, highlighting the beneficial role of PbI2 on device performance. Using high-resolution transmission electron microscopy we show the location of PbI2 within the active layer and propose a nucleation and growth mechanism. We discover that during the annealing that PbI2 forms mainly in the grain boundary regions of the MAPI films and that at certain temperatures the PbI2 formed can be highly beneficial to device performance – reducing current–voltage hysteresis and increasing the power conversion efficiency. Our analysis shows that the MAPI grain boundaries as susceptible areas that, under thermal loading, initiate the conversion of MAPI into PbI2

Careful interface design and engineering are “keys” to effectively implement a conformal 10 nm plasma-assisted atomic-layer-deposited NiO film as hole transport layer in a p–i–n perovskite solar cell architecture.