In　this　paper　the　vanishing　Debye　length　limit　(space　charge　neutral　limit)　of　bipolar　time-dependent　drift-diffusion　models　for　semiconductors　with　p-n　junctions　(i.e.,　with　a　fixed　bipolar　background　charge)　is　studied　in　one　space　dimension.　For　general　sign-changing　doping　profiles,　the　quasi-neutral　limit　(zero-Debye-length　limit)　is　justified　rigorously　in　the　spatial　mean　square　norm　uniformly　in　time.　One　main　ingredient　of　our　analysis　is　the　construction　of　a　more　accurate　approximate　solution,　which　takes　into　account　the　effects　of　initial　and　boundary　layers,　by　using　multiple　scaling　matched　asymptotic　analysis.　Another　key　point　of　the　proof　is　the　establishment　of　the　structural　stability　of　this　approximate　solution　by　an　elaborate　energy　method　which　yields　the　uniform　estimates　with　respect　to　the　scaled　Debye　length.